Optical switch pathway configuration using control signals

[0002] This application is a Continuation-In-Part of U.S. patent application Ser. No. 09/092,393 entitled “SENSING CONFIGURATION FOR FIBER OPTIC SWITCH CONTROL SYSTEM” filed on Jun. 5, 1998, now U.S. Pat. No. 6,097,858, Ser. No. 09/092,099 entitled “COMPACT OPTICAL MATRIX SWITCH WITH FIXED LOCATION FIBERS” filed on Jun. 5, 1998, now U.S. Pat. No. 6,097,860, and Ser. No. 09/092,400 entitled “OPTICAL SWITCH TARGETING SYSTEM” filed on Jun. 5, 1998, now U.S. Pat. No. 6,101,299.

[0003] The present invention relates, in general, to fiber optic switches that employ control signals for aligning fibers to be connected for transmission of communication signals therebetween. In particular, the present invention is directed to making a communication signal pathway over which a communication signal is transmittable in an optical switch coincident with a desired pathway between two fibers by transmitting a control signal on or off of the communication signal pathway.

[0004] Fiber optic systems are now in common use for transmitting optical communication signals i.e., optical signals modulated to encode desired information. The optical communication signals are transmitted across a network using optical fibers that support substantial transmission capacity with compact fiber bundles. Given the ever-increasing demands for improved signal quality and bandwidth, it is anticipated that the use of fiber optic communications will continue to increase for years to come.

[0005] One of the reasons that fiber optic networks have attracted attention in recent years relates to switching advantages. Because the communication signals in fiber optic networks are optical in nature, conventional electronic switching components can be eliminated. Instead, fiber optic communications lines are connected at a switch by carefully aligning the fiber ends of the lines to be connected for direct optical linkage. Such switching has proved advantageous in that switching can be accomplished quickly without unacceptable signal degradation. However, it will be appreciated that there is a continuous desire to increase the speed of operation and reduce signal losses at switch interfaces.

[0006] One of the most persistent challenges associated with optical switches is how to quickly and accurately align the fibers that are being connected, i.e., optically interfaced for signal communication therebetween. High speed is required to minimize lag times in the network. Accuracy is required to minimize signal losses. In this regard, it will be appreciated that even slight misalignments of the fiber ends will result in a significant loss of the power of the transmitted optical signal and, potentially, of the information encoded in the signal. Moreover, switch designers are continuously endeavoring to accommodate more fibers in smaller switches. Accordingly, alignment systems remain the focus of much research.

[0007] Conventional alignment systems typically employ radiation emitting devices (REDs), such as light or infrared radiation emitting diodes (“LEDs”), lasers or VCSEL lasers for fiber identification and alignment. Fiber identification relates to identifying the fibers that are to be connected for initial targeting and manipulating the switch targeting mechanisms so that the identified fibers are in rough optical alignment. In this regard, it will be appreciated that a typical switch includes a matrix of fiber ends on a first side of the switch and another matrix of fiber ends on a second side. Depending on the switch configuration, these matrices may optically interface directly, or via a folded optical path. In either case, it is generally a function of the switch to be able to optically connect any of the fibers on the first side to any of the fibers on the second side. The fiber identification process allows this connection to be initiated. Thereafter, a fiber alignment process fine tunes the connection to maximize signal transmission or minimize signal losses.

[0008] In order to facilitate the targeting and alignment processes, one or more REDs is typically mounted in known spatial relationship to each of the fibers of each matrix, e.g., adjacent to the fiber on the matrix structure. These REDs transmit radiation across the switch interface to the opposing matrix. In addition, an optical receiver is provided in conjunction with each fiber of each matrix. For example, the receiver may be incorporated into a cladding layer of a dual core optical fiber where the central fiber is used for transmission of communication signals. The receiver receives radiation from a RED or REDs of the opposing matrix and provides the received radiation to a detector/feedback system for controlling targeting. In this manner, the REDs can first be used to signal which of the fibers are to be connected. Thereafter, alignment can be optimized by analyzing the signal transmitted from the RED(s) associated with one of the target fibers to the receiver associated with the other and vice versa.

[0009] Although such conventional targeting and alignment systems have provided acceptable speed and accuracy, they impose certain limitations in switch designs. First, the REDs and receivers incorporated into the fiber matrices may limit the design of the array or impede array miniaturization. Moreover, the detectors used in such conventional systems generally include a large active area and a correspondingly low signal-to-noise ratio. The dual core fibers used for transmitting and receiving are also very expensive and difficult for switch manufacturers to reliably stock. It would therefore be advantageous to design a fiber optic switch that reduces or eliminates the need for dual core fibers and otherwise addresses limitations of conventional targeting and alignment systems.

[0010] The present invention is directed to systems for use in configuring an optical switch such that a communication signal transmittable over a communication signal pathway from a first fiber end may be transmitted along a desired pathway between the first fiber end and a second fiber end by configuring the switch to make the communication signal pathway coincident with the desired pathway. A feedback signal relating to the spatial relationship between the communication signal pathway and the desired pathway is generated by a control signal detector that detects a transmitted control signal. The present invention contemplates implementations of such systems employing control signals transmitted on-path with the communication signal pathway in a variety of optical switches. For example, a system employing on-path control signals may be implemented in a mirror based optical switch where the optical fiber ends are stationary and positionable mirrors direct the communication signal between selected fibers ends. Another example is an optical switch where the optical fiber ends are moveable and are pointed at one another in order to direct the communication signal between selected fiber ends. The present invention also contemplates various novel implementations of a system employing a control signal transmitted off-path of the communication signal pathway in a mirror-based optical switch.

[0011] According to one aspect of the present invention, a method for use in configuring an optical switch such that a communication signal transmittable from a first fiber end may be transmitted along a desired pathway between the first fiber end and a second fiber end includes transmitting a control signal over at least a portion of a communication signal pathway over which the communication signal is transmittable in the optical switch. Hence, the control signal is “on-path” with the communication signal pathway. The transmitted control signal is received by a control signal detector that is maintained in a known spatial relation relative to the desired pathway. A feedback signal relating to the spatial relationship between the communication signal pathway and the desired pathway is output by the detector. The feedback signal can be utilized in configuring the switch to make the communication signal pathway coincident with the desired pathway. For example, in a mirror based switch, the feedback signal may be utilized in controlling the position of one or more positionable mirrors of the optical switch in order to make the communication signal pathway and the desired pathway coincident. In a non-mirror based switch, the feedback signal may be utilized in moving the fiber ends such that they point at one another in order make the communication signal pathway coincident with the desired pathway.

[0012] According to another aspect of the present invention, the control signal is transmitted using a control signal transmitter and the generated control signal is directed onto the communication signal pathway using a first optical element. In this regard, the control signal transmitter may be a radiation emitting device (RED). The first optical element receives the communication signal on a first entrance pathway from the first fiber end and the control signal from the control signal transmitter on a second entrance pathway different from the first entrance pathway. The two signals are transmitted by the first optical element together on the communication signal pathway. In this regard, the communication and control signal may be of different wavelengths and the first optical element may transmit the two signals together on the communication signal pathway by means of a wavelength dependent mirror.

[0013] According to a further aspect of the present invention, the communication and control signals are separated from one another using a second optical element. The second optical element receives both signals on the communication signal pathway. The communication signal is transmitted by the second optical element on a first exit pathway towards the second fiber end. The control signal is transmitted by the second optical element towards the detector on a second exit pathway different than the first exit pathway. In this regard, the communication and control signals may be of different wavelengths and the second optical element may separate the communication and control signals by means of a wavelength dependent mirror.

[0014] According to an additional aspect of the present invention, the control signal is received using a detector that permits substantial transmission of the communication signal therethrough but detects the control signal. In this regard, the control and communication signals may have differing wavelengths and the detector may permit transmission of signals therethrough on a wavelength dependent basis. This aspect of the present invention permits locating the detector in the desired pathway and eliminates the need for a second optical element for separating the control signal from the communication signal.

[0015] According to yet another aspect of the present invention, a method for use in configuring a mirror based optical switch having a plurality of positionable mirrors such that a communication signal transmittable from a first fiber end may be transmitted along a desired pathway between the first fiber end and a second fiber end includes transmitting a control signal over a control signal pathway in the optical switch. The control signal pathway is separate from a communication signal pathway over which the communication signal is transmittable in the optical switch. Hence, the control signal is transmitted “off-path” from the communication signal pathway. Although off-path from the communication signal pathway, the control signal pathway has a known spatial relation relative to the communication signal pathway. In this regard, the control signal pathway may be substantially parallel with the communication signal pathway. The control signal is received by a control signal detector that is maintained in a known spatial relation relative to the desired pathway. A feedback signal relating to the spatial relationship between the communication signal pathway and the desired pathway is output by the detector. The feedback signal can be utilized in positioning at least one mirror of the optical switch in order to make the communication signal pathway and the desired pathway coincident.

[0016] According to yet a further aspect of the present invention, the control signal may be generated using a control signal transmitter, such as a RED. Both the control and communication signals are directed to the same mirror of the optical switch using a first optical element. The first optical element receives the communication signal on a first entrance pathway from the first fiber end and transmits the communication signal on the communication signal pathway towards the mirror. The control signal is received from the transmitter on a second entrance pathway separate from the first entrance pathway and is transmitted by the first optical element on the control signal pathway towards the mirror. In this regard, the communication and control signals may be of different wavelengths and the first optical element may include a wavelength dependent mirror that transmits the control and communication signals on their respective pathways.

[0017] According to one more aspect of the present invention, a second optical element receives the communication and control signals and directs the communication signal towards the second fiber end and the control signal towards the detector. The communication signal is received by the second optical element on the communication signal pathway and transmitted thereby on a first exit pathway towards the second fiber end. The control signal is received by the second optical element on the control signal pathway and transmitted thereby towards the detector on a second exit pathway separate from the first exit pathway. In this regard, the second optical element may transmit the communication and control signals on their respective exit pathways by means of a wavelength dependent mirror.

[0018] According to yet an additional aspect of the present invention, an apparatus for use in configuring an optical switch such that a communication signal transmittable from a first fiber end may be transmitted along a desired pathway between the first fiber end and a second fiber end includes a control signal transmitter and a control signal detector. The control signal transmitter transmits a control signal for determining the spatial relationship between a communication signal pathway over which the communication signal is transmittable in the optical switch and the desired pathway. In this regard, the control signal may be transmitted over at least a portion of the communication signal pathway (i.e. on-path) in a variety of optical switches, and, where the optical switch is mirror based, the control signal may also be transmitted on a control signal pathway separate from the communication signal pathway (i.e. off-path). The control signal detector is disposed in a known spatial relation relative to the desired pathway. The control signal detector receives the transmitted control signal and outputs a feedback signal relating to the spatial relationship between the communication signal pathway and the desired pathway. The feedback signal output by the control signal transmitter can be utilized to configure the switch, for example by positioning a mirror, in order to make the communication signal pathway and the desired pathway coincident.

[0019] These and other aspects and advantages of the present invention will be apparent upon review of the following detailed description when taken in conjunction with the accompanying figures.

[0020] For a more complete understanding of the present invention and further advantages thereof, reference is now made to the following Detailed Description, taken in conjunction with the drawings, in which:

[0021] FIGS. 1A-1C are schematic diagrams of exemplary fiber optic switch connections in connection with which the control system of the present invention may be implemented;

[0022] FIG. 2 illustrates the spatial relationship between REDs and fiber ends in accordance with the present invention;

[0023] FIG. 3 is a graph illustrating a RED pulsing sequence for targeting and alignment in accordance with the present invention;

[0024] FIG. 4 is a graph illustrating an alternative RED pulsing sequence for targeting and alignment in accordance with the present invention;

[0025] FIG. 5 illustrates an alternative arrangement of REDs and fiber ends in accordance with the present invention;

[0026] FIG. 6 is a further alternative arrangement of the REDs and fiber ends in accordance with the present invention;

[0027] FIG. 7 illustrates a five RED pulsing sequence for targeting and alignment in accordance with the present invention;

[0028] FIG. 8 illustrates an alternative five RED pulsing sequence for targeting and alignment in accordance with the present invention;

[0029] FIG. 9 illustrates a frequency modulated implementation for five RED targeting and alignment in accordance with the present invention;

[0030] FIG. 10 shows a side view of an off path sensor arrangement in accordance with the present invention;

[0031] FIG. 11 is a perspective view of the mirror block of FIG. 10;

[0032] FIG. 12 is a graph depicting the wavelength response of the mirror block of FIG. 11;

[0033] FIG. 13 is a top view showing a sensor design in accordance with the present invention;

[0034] FIG. 14 is a top view showing an alternative sensor design in accordance with the present invention;

[0035] FIG. 15 is a top view showing a further alternative sensor design in accordance with the present invention;

[0036] FIG. 16 is a top view showing a sensor design with separate targeting and alignment detector surfaces in accordance with the present invention;

[0037] FIG. 17 is a top view showing an alternative sensor design employing separate targeting and alignment detector surfaces in accordance with the present invention;

[0038] FIG. 18 is a side view depicting a portion of a switch incorporating a five RED fiber arrangement in accordance with the present invention;

[0039] FIG. 19 is a side view showing control components associated with a single fiber in accordance with the present invention;

[0040] FIG. 20 is a perspective view showing the control components associated with a single fiber incorporated into a tray structure in accordance with the present invention;

[0041] FIG. 21 is a perspective view showing a chassis in accordance with the present invention;

[0042] FIG. 22 illustrates a tray structure for housing two fiber ends with related control elements in accordance with the present invention;

[0043] FIG. 23 top view showing a sensor design that can be used in connection with the control components of FIG. 19;

[0044] FIG. 24 is a circuit diagram of circuiting for use in connection with the sensor design of FIG. 23;

[0045] FIG. 25 is a top view of a moveable mirror assembly for use in connection with the control components of FIG. 19;

[0046] FIG. 26 is a flow chart illustrating a closed loop servo targeting and alignment control processed in accordance with the present invention;

[0047] FIGS. 27A-27C show various sensor configurations for addressing the potential problem of sensor current resulting from signals impinging in the detector outside of the various sensor areas;

[0048] FIG. 28 shows an alternative optical configuration for a switch in accordance with the present invention;

[0049] FIGS. 29A-29C show a chassis implementation in accordance with the present invention;

[0050] FIGS. 30A and 30B illustrate the operation of the focusing optics employed in accordance with the present invention;

[0051] FIGS. 31-33 illustrate alternative configurations of a beam directing unit in accordance with the present invention;

[0052] FIG. 34 illustrates one embodiment of an optical switch in which an on-path control signal system in accordance with the present invention is implemented;

[0053] FIG. 35 illustrates another embodiment of an optical switch in which an on-path control signal system in accordance with the present invention is implemented;

[0054] FIG. 36 illustrates an additional embodiment of an optical switch in which an on-path control signal system in accordance with the present invention is implemented;

[0055] FIG. 37 illustrates one embodiment of an optical switch in which an off-path control signal system in accordance with the present invention is implemented;

[0056] FIG. 38 illustrates a side view of one embodiment of an optical unit in accordance with the present invention shown interfaced with a similarly configured optical unit on the opposing side of a switch interface;

[0057] FIG. 39 illustrates a side view of one embodiment of a beam directing element of the optical units of FIG. 38;

[0058] FIGS. 40A-L illustrate top views of alternative configurations of sensor surfaces in accordance with the present invention;

[0059] FIGS. 41-50 illustrate side views of alternative configurations of optical units in accordance with the present invention;

[0060] FIG. 51 is cross-sectional view of a fiber illustrating the relationship between acceptance and numerical aperture;

[0061] FIG. 52 illustrates various optical parameters relevant to the present invention; and

[0062] FIG. 53 illustrates an imaging relationship geometry in accordance with the present invention.

[0063] The fiber optic control system of the present invention is useful in a variety of contexts where it is desired to optically link opposing optical fibers. In the following description, the fiber optic control system is set forth in the context of certain N×N optical switch embodiments, i.e., switches for communication networks that selectively connect any of N first fiber lines with any of N second fiber lines. It will be appreciated, however, that various aspects of the invention have broader application.

[0064] The control system of the present invention preferably employs optical control signals to provide feedback for closed-loop servo-targeting/alignment control. In this regard, the control system involves subsystems for optical signaling, for signal detection, for determining desired optical path manipulations in response to detected control signals and for actuating the desired optical path manipulations. An important aspect of the present invention relates to an off-path control signal source and/or detector configuration as well as associated control systems/control signal pathway configurations. However, it is believed that this aspect of the present invention and the attendant advantages will be best appreciated upon gaining a full understanding of the optical switch environment and the various subsystems involved in targeting and alignment control. Accordingly, the following description includes: 1) a general discussion of the optical switch environment of the present invention; 2) a discussion of various optical signaling implementations; 3) a discussion of various optical signal detection implementations; 4) a description of practical embodiments incorporating specific signaling and detection implementations in accordance with the present invention; 5) a description of several exemplary implementations of an on-path control signal system; and 6) a description of an exemplary implementation of an off-path control signal system.

[0065] Referring to the Figures, FIGS. 1A-1C are schematic diagrams showing examples of possible configurations of N×N optical switches in connection with which the control system of the present invention may be implemented. Each of the illustrated embodiments depicts a 16×16 switch, although practical embodiments may include less or substantially more, e.g., 256×256, possible line connections. FIG. 1A shows an opposing chassis configuration for a switch 10. The switch 10 allows for selective connection between any of the first side lines 12 and any of the second side lines 14. Such connections allow for bi-directional communication of information (e.g., voice, video, data) as between the connected lines 12 and 14. Each of the lines generally includes an optical fiber for optically transmitting information as pulses of light or other electromagnetic radiation. It will thus be appreciated that the switch 10 can be part of a communication network.

[0066] Additional features of the switch 10 can be understood by reference to the schematic diagram of FIG. 1A. In this regard, the illustrated switch 10, includes first 16 and second 18 optical chassis separated by a transmission area 20. Each chassis includes windows 22 associated with lines 12 or 14 such that optical signals can be transmitted across the transmission area 20 to effect a “connection” and allow optical signal communication as between any of the lines 12 and any of the lines 14. Although the chassis 16 and 18 are illustrated in opposing relationship, it will be appreciated that other physical arrangements, such as noted below, and associated folded optical pathways (e.g., using lenses and mirrors) may be utilized. Similarly, even in the case of an opposing chassis configuration, folded optical pathways may be utilized to reduce the dimensions of the switch 10 for a given optical pathlength across the transmission area.

[0067] FIG. 1B shows an alternative, side-by-side configuration for a switch 10′. Again, the switch 10′ allows for selective connection between any of the first side lines 12′ and any of the second side lines 14′. Such connections are effected via a folded optical pathway, generally indicated by phantom line 15, using a mirror 17. In this regard, it will be appreciated that the “first side” and “second side” of the switch 10′ are defined relative to a signal transmission pathway and are not necessarily spatially opposite sides. The illustrated folded configuration may be used, for example, to reduce the depth, D, of the switch 10′.

[0068] FIG. 1C shows a further alternative, interspersed configuration for a switch 10″. The switch includes a single chassis 16″ and a mirror 17′. Within the chassis 16″, the first and second side lines are interspersed in the rows of a matrix configuration. In the illustration, for example , the first side lines may be associated with the shaded windows 19 and the second side lines may be associated with the unshaded windows 21. Such a configuration may be employed to reduce both the depth, D, and the width, W, of the switch 10″. Although only three configurations have been shown and described, it will be appreciated that other configurations are possible.

[0069] The control system of the present invention allows for selection and targeting of optical pathways across a switch, such as switches 10, 10′ and 10″ as well as alignment of the lines to be connected. It will be appreciated that the process for making a connection between a selected one of the first side lines and a selected one of the second side lines requires that the associated optical transmission/reception elements be targeted at and aligned with one another. Typical system requirements specify that optical losses across the switch should be minimal. Consequently, accurate targeting and alignment is of significant importance. Moreover, speed of switch operation is an important consideration and rapid targeting and alignment is therefore highly desirable. In addition, compact construction is an important consideration. The control system of the present invention as set forth below addresses these concerns.

[0070] In particular, the control system of the present invention employs a number of radiation emitters, such as radiation emitting diodes (REDs), associated with each of the first and second side lines. These REDs, which may emit infrared radiation, are used in a coordinated manner to quickly 1) identify the targeted lines (first side and second side) and 2) provide closed-loop feedback for servo-targeting/alignment control. In this context, targeting refers to signaling to identify the lines that are to be connected and manipulating the appropriate control elements (as will be described below) to roughly configure an optical pathway between the lines so as to effect a connection. Alignment refers to fine-tuning the connection for optimized communication signal transmission. The immediately following description sets forth a number of implementations for targeting and alignment signaling. These generally involve: 1) using the same REDs for targeting and alignment signaling; 2) using dedicated REDs for targeting and separate dedicated REDs for alignment; 3) conducting target signaling and alignment signaling in separate, overlapping or the same time intervals; and 4) implementing the signaling in a pulsed or digital format or by way of signal modulation (i.e., frequency modulation). It will be appreciated that other implementations are possible in accordance with the present invention.

[0071] FIG. 2 generally represents a front or end-on view through one of the illustrated chassis, e.g., chassis 16 (FIG. 1A). That is, the vantage point of FIG. 2 is generally aligned with optical pathways between the chassis. Each of the fiber lines in chassis 16 is associated with a fiber end 24 and, typically, a lens for focusing radiation entering/exiting the associated line. For present purposes, the illustrated rows and columns of fiber ends 24 may be thought of as spatially corresponding to the rows and columns of lines 12. In the embodiment of FIG. 2, each fiber end 24 is surrounded by four REDs 26. The dimensions of the fiber ends 24 may vary from switch to switch or as between individual fibers of a switch. In FIG. 2, the fiber ends 24 are significantly magnified as they may appear through lenses for focusing signals onto the fiber ends 24 and focusing signals transmitted by fiber ends 24. It will be appreciated that the fiber ends 24 and REDs may be located at different positions (e.g., depths relative to the vantage point of FIG. 2) along their common optical path so long as the REDs have a known spatial relationship to the associate fiber end 24 relative to the optical path. As will be understood from the description below, each of the lines 12 and 14 also includes a radiation sensor or sensors for receiving radiation from the REDs. By comparing the signals received at a targeting line 12 or 14 from the REDs of a targeted line 14 or 12, e.g., the locations of incidence on a sensor of the signals from the various REDs, feedback information can be derived to better align the optical transmission pathway relative to the targeted/targeting lines 12 and 14. In this regard, the targeted and targeting lines 12 and 14 can be adjusted cooperatively and simultaneously for optimal transmission.

[0072] In one implementation corresponding to the illustrated four RED per fiber line configuration, the control system of the present invention uses controlled pulsing of the REDs for both target selection/identification and servo-targeting/alignment control. FIG. 3 illustrates an appropriate pulsing sequence for the four REDs associated with a targeted line. The pulse profiles shown correspond to on/off cycling of the REDs over time to effectively provide digital signaling. As shown, in this implementation, all four REDs are first pulsed simultaneously (i.e., during a first time period) to identify the target, i.e., the fiber end and/or focusing lens with which the REDs are associated. In this regard, the initial pulse sequence can convey a target identification code. Thereafter, the four REDs are pulsed sequentially for servo-alignment control that identifies the location of the associated fiber. The coding may be, for example, a simply binary code, a Manchester code or any other code sufficient to provide the target identification information. In this manner, both target identification and alignment control are effected quickly using signals from the four REDs. It is noted that prior target identification schemes have required a long series of column and row identification signals involving sequentially coordinated pulsing of the N×N array.

[0073] FIG. 4 illustrates an alternative pulsing sequence where the servo-control pulses are modulated to convey target identification information. That is, the four REDs are operated in sequential time periods for alignment purposes. Within the time period that a particular RED is operated, it is pulsed to convey a target identification code. In this manner, the targeting and servo-control functions are combined for possibly faster operation.

[0074] FIG. 5 shows an alternative fiber/RED configuration for use in target identification and alignment control. In the illustrated embodiment, a fifth RED 28 for each fiber end 30 is provided for target identification separate from the four alignment control REDs 32. It will be appreciated that the illustrated fiber ends 30, servo-alignment control REDs 32 and the target identification RED 28 may be located at different positions (e.g., depths relative to vantage point of FIG. 5) along their common optical path. In addition, the dimensions of the fiber ends 30 may vary from switch to switch or as between fibers of a switch. The alignment control REDs 32 and target identification RED are disposed in known, but different, spatial relationship to the corresponding fiber end 30 relative to the associated optical pathway, thereby allowing for separate detection of the target identification and alignment signals. This embodiment is further associated with alternative sensor configurations as described below.

[0075] FIG. 6 shows a further alternative fiber/RED configuration involving a fifth RED 28′ for separate target identification. In the embodiment of FIG. 6, the four (per fiber) servo-alignment control REDs 32′, as well as the target identification REDs 28′ are spatially offset from the fiber ends 30′ relative to the optical paths associated with the fiber ends 30′. It will thus be appreciated that no particular arrangement of the alignment REDs 32′ relative to the fiber ends 30′ or target identification REDs 28′ is required, provided that the spatial relationship between the REDs 32′ and fiber ends 30′ relative to the optical pathway is known.

[0076] FIG. 7 shows a pulsing sequence for target identification and servo-alignment control using a five RED/fiber end arrangement such as illustrated in FIGS. 5-6. The REDs designated #1, #2, #3 and #4 in FIG. 7 generally correspond to the servo-alignment REDs 32 or 32′ of FIGS. 5 or 6 and the RED designated #5 generally corresponds to target identification REDs 28 or 28′. As shown, the pulse sequence is initiated by a pulsed target identification code by RED #5. Thereafter, REDs #1-#4 are pulsed sequentially for alignment control.

[0077] FIG. 8 shows an alternative pulsing sequence for a five RED/fiber end arrangement where the pulsed target identification code and servo-targeting control pulses are transmitted in simultaneous or temporally overlapping relationship. It will be appreciated that the pulsed target identification code can be readily distinguished from the sequential servo-alignment control pulses as these pulse sets can be separately detected as described below.

[0078] FIG. 9 shows an alternative signaling implementation for a five RED/fiber end arrangement where the pulses from all five of the REDs are transmitted in simultaneous or temporally overlapping relationship. In this implementation, the pulses of the various REDs #1-#5 can be distinguished by the sensor or sensors because they are modulated at differing frequencies. For example, the various signals can be resolved through appropriate signal analysis or by use of band pass filters or the like to separate a resulting composite signal into its constituent frequency-related components. Based on the foregoing examples, it will be understood that many signaling implementations are possible with respect to the number of REDs, the arrangement of REDs, the use of common or dedicated REDs for target identification and alignment, the temporal relationship between the transmitted target identification and alignment signals and the way of encoding information into the signals.

[0079] From the foregoing discussion, it will be appreciated that the control signals (i.e., the target identification and alignment signals) and the communication signals (the signals carried by the fiber lines) are generally transmitted along a common pathway within the switch interface, or along pathways having a known spatial relationship to one another. Indeed, the relationship between the control signal pathway and communication signal pathway is an integral part of the desired closed-loop servo-control system. An important part of a preferred control system of the present invention relates to separation of the control signals and communication signals. In particular, it is desirable that the control signals and communication signals travel along closely related paths, for example, involving the same mirrors, lenses and other optics, thereby eliminating sources of control error due to optical path differences. However, it has been found that it is also useful to separate the control signals from such a common optical pathway for detection so as to enhance detector design options and performance.

[0080] This separation can be implemented by a detector unit including an off-path sensor. An embodiment of such a unit 40 is schematically illustrated in FIG. 10. The unit 40 includes a lens 42 for focusing radiation entering/exiting a fiber line 44 at the switch interface. In the illustrated embodiment, a signal separator 46 is disposed between the lens 42 and fiber line 44 for separating incident signals, on a wavelength dependent basis, between a first, communication pathway, generally indicated by arrow 43, from the lens 42 to the line 44 via separator 46 and a second, detection pathway, generally indicated by arrow 45, from the lens 42 to a sensor assembly 48 via the separator 46. Different wavelength bands can be used for targeting signals and communication signals such that the separator 46 selects between the first and second paths based on wavelength. For example, where the communication signals are transmitted as infrared radiation having a wavelength of at least 1310 nm (λ>1310 nm), the REDs may be near infrared radiation emitting diodes (λ<1310 nm) or light emitting diodes (for emitting visible spectrum radiation). In this regard, the communications signals may have wavelengths of 1310 and/or 1550 nm, and the REDs may have wavelengths of 880 and/or 950 nm.

[0081] In this regard, the signal separator 46 can be, for example, various types of dichroic beam splitters such as a beam splitter cube, a coated filter or a pellicle-based filter. The illustrated separator 46, as best shown in FIG. 11, is a beam splitter cube formed from two prismatic elements 50 and 52. At least one of the faces at the interface between the elements 50 and 52 can be coated such that the splitter has a filtering/reflecting response as generally illustrated in FIG. 12. It will be appreciated that the control signal wavelengths for this embodiment can be selected to be in the wavelength range below about 1000 nm whereas the communication signals will be in the wavelength range above about 1200 nm.

[0082] FIGS. 13-17 show a number of possible configurations for the radiation-sensitive surface(s) of sensor assembly 48. The radiation-sensitive or sensor surfaces may be formed from any of various near infrared sensitive materials for providing an electrical signal in proportion to an incident radiation signal. The electrical signals can be read-out from the sensor surface by using electrodes as is well-known. The partitions in the sensor surfaces as discussed below are formed by electrically isolating portions of the sensor surfaces such that the signals from the various partitioned areas can be separately detected. Alternatively, CCD-based detectors or any other appropriate sensor systems may be employed. It is preferred to use a silicon-based detector, as these are generally sensitive below 1100 nm and not sensitive above 1200 nm, so stray radiation from the communication signal will not substantially influence it.

[0083] FIG. 13 shows a configuration employing a single, continuous sensor surface 54 for use in connection with a four RED/fiber embodiment as described above. Images 56 of the four REDs fall on an edge of the sensor surface 54 when the associated fiber line is properly aligned such that signals of substantially equal strength are received from each of the REDs. For example, Referring to FIGS. 2, 10 and 13, where the REDs are arranged around the fiber end relative to the associated optical pathway as shown in FIG. 2, the location of sensor surface 54 relative to pathway 45 generally corresponds to the location of fiber 44 relative to path 43. Moreover, the detector surface 54 can be located such that paths 43 and 45 are substantially equal in length. In this manner, lens 42 focuses communication signals substantially on the plane of the fiber end and focuses control signals substantially in the plane of the sensor surface.

[0084] The detector surface 54 is read out to provide output signals indicative of the received optical signals from the four REDs. In this regard, the signals from the various REDs may be distinguished due to, for example, differing frequency modulations. The relative strengths of the output signals can then be analyzed by a processor to obtain the encoded target identification information and alignment information. More particularly, the encoded information is used to determine the position of the fiber to be targeted and the optical pathway for the connection is roughly configured to form the optical connection. The signals from the REDs are then analyzed for alignment purposes. In this regard, if a signal from a given RED is very strong in relation to its diametrically opposed RED (relative to surface 54), the processor would be able to determine that an alignment correction was required relative to a corresponding axis. Such a correction can be related to a particular correction to be implemented, for example, by bending the end of a fiber using a piezoelectric bender to vary a signal transmission angle or moving a mirror within the switch interface to redirect the signal transmission pathway. The required correction is determined based on knowledge of the RED positions relative to the signal transmission pathway, as well as the spatial relationship between the detector surface 54 and the associated fiber end. It will be appreciated that the four REDs (arranged in two opposing pairs) allow for convenient two-dimensional servo targeting and alignment control. The REDs may be arranged to provide control feedback directly correlated to, for example, two pivoting axes of a moveable mirror. The mirror may be constructed as a micro-machined chip mounted mirror surface, which is hinged or gimbaled to pivot about two orthogonal axes. Such pivotal motion is controlled by varying an electromagnetic field. Accordingly, control of the reflecting surface is actuated in response to appropriate electrical signals, based on analysis of the output signals from the detector, so as to vary the electromagnetic field at the reflecting surface, thereby pivoting the reflecting surface to the appropriate position to effect the required path correction. Such micro-machined, moveable mirrors are available, for example, from Texas Instruments.

[0085] In FIG. 14, four partitioned quadrant sensor areas 58 are employed for enhanced response and signal-to-noise ratio. In particular, the partitions allow for separately detecting the signals from the various REDs so as to better distinguish between such signals, and the smaller detector areas provide improved signal to noise ratio. FIG. 15 includes two partitioned sensor areas 60 per RED for further improved response. In this regard, it will be appreciated that substantially the entire cross-section of each of the control signals is incident on the partitioned sensor surface for improved optical efficiency. In addition, the two sensor areas per signal configuration allows for differential sensing, i.e., comparing the signal portion received by an inner sensor area to the signal portion received by the corresponding outer area to determine a radial location of incidence of the signal. The illustrated configuration implements smaller area sensor surfaces for improved signal to noise ratio. As described above, the output signals read out from the various sensor areas 58 provide an indication of the location of incidence of the optical signals from the various REDs. These incidence locations, in turn, provide feedback regarding the targeting/alignment state of the associated optical pathway. Appropriate pathway corrections can be implemented based on analysis of the received optical signals from the REDs.

[0086] FIG. 16 corresponds to a five RED embodiment as described above. The detector assembly 48 includes a quadrant sensor surface 62 for detecting signals from the four servo-alignment control REDs and a separate sensor surface 64 for detecting signals from the target identification RED. The quadrant sensor surface 62 provides alignment information as generally discussed above in connection with FIGS. 14-15. Sensor surface 64 receives a signal from a dedicated targeting RED that is offset relative to the alignment REDs such as shown, for example, in FIG. 5. The targeting sensor surface 64 can be somewhat larger than the alignment sensor surface 62 to assist in target searching. In this regard, it will be appreciated that noise may be less of a concern in connection with targeting and only rough optical path configuring is required. Preferably, the sensor surface is dimensioned to facilitate searching for a targeting signal from a targeting RED associated with a given fiber without detecting signals from targeting REDs associated with adjacent fibers. In addition, the sensor surface 64 may be designed to provide an indication concerning the location of incidence of the RED signal on the sensor surface 64. For example, such an indication may be obtained by comparing output signals detected at different read out electrodes. In this manner, preliminary feedback concerning alignment may be obtained to facilitate the alignment process using output from the alignment sensor surface 62.

[0087] In FIG. 17, the identification sensor assembly 66 includes multiple targeting sensor areas 68 for improved response, as well as course alignment. That is, by separately reading out the sensor areas, and based on knowledge of the spatial relationship between the targeting RED and the targeted fiber, an initial indication of alignment is provided. For example, if the targeting signal is received in equal portions by each of the sensor areas 68, this may indicate that the fibers to be connected are in close alignment, although feedback from the alignment REDs and sensor(s) would be useful in providing more accurate, two-dimensional alignment information. The illustrated partitioned targeting sensor surface also allows for reduction in targeting sensor noise. Moreover, it will be appreciated that, in the case of separate targeting and alignment sensors such as shown in FIGS. 16 and 17, different sensor designs and materials may be employed for the alignment and targeting sensors to reduce cost and/or accommodate the differing functional requirements of the respective sensors. These sensor design options are facilitated by the control system design including an off-path sensor configuration and a signal separator assembly as described below.

[0088] FIGS. 27A-27C show further alternative sensor configurations. A potential problem in chip mounted sensors relates to sensor currents produced by photons incident on the detector outside of the designated sensor areas. The sensor surfaces can be defined by depositing a diode material, such as a P++ material, on selected areas of the chip substrate. However, an associated depletion area will generally extend outwardly from the sensor surface defined by deposition of the diode material. Photons absorbed in the depletion area may create a current in the sensor. As a result, the sensor can sense photons outside of the desired sensor area, thereby creating an element of error and potentially rendering the system inoperative.

[0089] FIG. 27A shows one sensor configuration for addressing this potential problem. The illustrated sensor 200 is fabricated on a chip 202. The sensor 200 includes four quadrant alignment sensor surfaces 204, such as described above, and four quadrant targeting sensor surfaces 206. As shown, the alignment sensor surfaces 206 are formed within two of the targeting sensor surfaces. Connections to the alignment sensor surfaces 206 for reading out alignment signals are established by conductive leads 208 terminating in pads 210. Electrical contacts 212 can be welded to the pads 210. Connections to the targeting sensor surfaces 206 for reading out targeting signals are established by metallization areas 214 that provide a bonding surface for read-out electrical contacts 216. Contacts 218 are used to interconnect the metallization areas associated with the upper quadrant targeting sensor areas 206 of the left and right sides, respectively, to allow for a single read out contact for the two separate metallization areas associated with each such targeting sensor area 206. Appropriate insulating materials are provided between the various sensor surfaces and conductive elements for electrical isolation as desired.

[0090] The illustrated construction has certain construction/operational advantages. It is desirable to reduce the need for metallic masking near the sensor surfaces. Such masking can short to the sensor surfaces and may also reflect light back to the surfaces resulting in increased noise. In the illustrated embodiment, no such masking is required adjacent to the alignment sensor surfaces 204. Photons incident in the narrow area between the alignment surfaces 204 and targeting surfaces 206 will be collected by the closest sensor surface 204 or 206. Accordingly, the effective areas of the surfaces 204 and 206 extend to the mid-line of the narrow area in-between, and the surfaces can be dimensioned accordingly. Large metallization areas 214 can still be used to cover much of the chip 202 and provide easily accessible bonding pads without requiring large metallic masking adjacent to the alignment surfaces 204.

[0091] Another solution for the problem of migrating photons adjacent to the sensor surfaces is illustrated in FIG. 27B. In this case, a guard ring 232 is formed around the alignment sensor surfaces 222 and the targeting sensor surfaces 224. The various sensor surfaces 222 and 224 are connected to metallic bonding pads 226 by conductive leads 228. Insulation 230 is disposed between the diffusion areas 232 of chip 234 and the leads 228 for isolation. Similarly, an insulating material such as SiO₂may be patterned to isolate the guard ring 232 from the leads 228 as necessary. The guard ring 232 is used to collect current due to photons incident outside of the sensor surface 222 and 224. The effective areas of each of the sensor surfaces 222 and 224 will extend to the mid-line of the area between itself and an adjacent sensor surface or guard ring. Pad 235 provides electrical connections to the guard ring 232.

[0092] FIG. 27C shows a combination of the designs of FIGS. 27A and 27B. In particular, upper quadrants of the targeting sensor areas 238 are configured to surround the alignment sensor areas 236. In addition, a guard ring 240 is provided around the sensor surfaces 238. Metallization 242 is provided to establish bonding surfaces for the sensor surfaces 236 and 238. Pad 244 provides an electrical connection to the guard ring. For purposes of clarity, the various insulating layers for electrical isolation have been omitted from the Figure. The illustrated construction thereby allows for convenient and accurate alignment and targeting detection with reduced diffusion noise.

[0093] FIG. 18 is a schematic diagram showing a portion of an N×N switch employing an off-path sensor configuration with a signal separator assembly. In the illustrated switch, each unit 70 includes a fiber 72, a lens 74, a signal separator 76 which may be a beam splitter cube as described above, a sensor unit 78, servo-alignment REDs 80, and a separate target identification RED 82. Not shown in FIG. 18 are the components for computing and actuating the optical path manipulations required for targeting and alignment. These components will be described below. FIG. 18 does illustrate a number of preferred characteristics of the inventive control system. First, it is noted that the various control elements are provided in connection with each of the units 70 on either side of the switch interface 84. It will thus be appreciated that targeting and alignment as between two fibers 72 is a cooperative process involving control components associated with each fiber 72. Moreover, multiple simultaneous connections can thereby be accommodated. In addition, the REDs 80 and 82 may be located away from the fibers 72 as shown in FIG. 18, for example, at a plane of a lens 74 or other optical element.

[0094] FIG. 19 is a partial schematic diagram showing the components associated with a single fiber of an optical switch. The components generally include a fiber assembly 86, a signal separator 88, a sensor unit 90, a lens assembly 92, stationary mirror 94, targeting RED 96, moveable mirror assembly 98 with mounted alignment REDs 100, window 102 and a processor 104. Each of these components is described in turn below.

[0095] The fiber assembly 86 includes a conventional optical fiber 106 for use in transmitting optical communication signals, a ferrule 108, and a fiber cable 110 including strength members 112 formed from Kevlar or other suitable material. The strength members 112, which impart strength to the cable 110 and allow the cable 110 to flex without damaging the fiber 106, are generally wrapped about the fiber 106, set in an adhesive and encased within the cable sleeve. The resulting cable 110 is typically about 2-3 mm in diameter. The ferrule 108, which may be formed from glass, ceramic or other materials, holds the bare fiber 106 adjacent to the signal separator 88. In this regard, the fiber/ferrule may be glued to the signal separator 88 using an adhesive having an index of refraction matched to those of the fiber 106 and separator 88 so as to minimize reflection at the interface. The fiber 106 and ferrule 108 are preferably polished together.

[0096] The separator 88 separates the control signals from the communication signals so that the control signals are received by the sensor unit 90 and the communication signals are received by fiber 106. This separation can be achieved using a beam splitter, coated filter, pellicle based filter or other mechanism for distinguishing between and separating the respective signals based on an optical characteristic of the signals such as wavelength. The illustrated separator 88 is a dichroic beam splitter, formed from two prismatic blocks 114 and 116 having a wavelength dependent response as discussed above. In this manner, the communication signals, which may have a wavelength of 1310 nm or 1550 nm, are transmitted to the fiber 106 and the control signals, which may have a wavelength of 880 nm or 950 nm, are reflected to the sensor unit 90. This response is achieved by applying an appropriate coating on a surface of at least one of the blocks 114 or 116 at the block interface to effectively define an optical band pass filter for passing the communication signals and reflecting the controls signals.

[0097] It is desirable to locate the sensor unit 90 such that the optical path length from the lens assembly 92 to the sensor unit 90 is approximately the same as the optical path length from the lens assembly 92 to the fiber 106. In this manner, the lens assembly 92 can focus the communication signals on the fiber 106 as desired and focus the control signals on the plane of the sensor surface of sensor unit 90 for enhanced detection. However, it will generally be impractical to bond the sensor unit 90 to the separator 88 such that the sensor surface is closely adjacent to the lower surface of lower block 116. Accordingly, the lower block 116 of the separator 88 may be somewhat smaller than the upper block 114 so that the sensor unit 90 can be properly positioned.

[0098] From the foregoing discussion, it will be appreciated that proper positioning and alignment of the lens assembly 92, separator 88, sensor unit 90 and fiber assembly 86 is a matter of some importance. These components can be assembled in the following manner to ensure proper positioning and alignment. First, the fiber 106 and ferrule 108 are glued to the upper block 114 using an index matched adhesive. The sensor unit 90 is then placed roughly in position relative to the bonded unit formed by the fiber 106 and block 114. The lower block 116 is then placed in position against the upper block 114 over the sensor unit 90. The sensor unit 90 can then be moved in three dimensions until the sensor surface is superimposed on the end of the fiber 106, as seen by the eye from the perspective corresponding to the location of lens assembly 92, and the various components are glued in place to maintain the alignment. The lens assembly 92 is then positioned using an adjustable mount so that the signals are focused on the fiber 106 and detector surface.

[0099] The sensor unit 90 includes a sensor chip 118 mounted on a printed circuit board 120. The sensor surface(s) are fabricated on the chip 118. The associated circuitry may be located on the chip 118 or on separate chips mounted on the board 120. FIGS. 23 and 24 show one sensor surface configuration and related circuitry. The illustrated sensor surface 22, which corresponds to a four RED embodiment for alignment and/or targeting, is partitioned by quadrants and includes inner and outer sensor areas within each quadrant, for a total of eight sensor areas (designated 1-8 in FIG. 23). As shown, each of the sensor areas (1-8) is associated with a bonding pad 124 for electrical connection. The partition areas between the quadrants are used to run electrical leads to the inner surfaces (1-4). The control system geometry is configured such that signals from one of the REDs are received in each of the quadrants. In order to obtain information regarding the radial location of incidence of signals, the detection scheme may be differential by quadrant, i.e., the output from area 1 may be compared to that from 5; the output from area 2 may be compared to that of area 6; area 3 may be compared to area 7; and area 4 may be compared to area 8.

[0100] FIG. 24 shows a simple circuit for processing the outputs from a quadrant pair; in this case, area 1 and area 5. The outputs from area 1 and area 5 are provided as the inputs (designated 1 and 5) of an operational amplifier 126. The output (designated 1-5) from amplifier 126 is therefore proportional to the difference between the signals from area 1 and area 5. This output value, in turn, is proportional to a radial location of incidence of an optical signal in the associated quadrant. Similarly, values are obtained for the other three quadrants relating to radial locations of signal incidence in those quadrants. These values are provided to processor 104, which may be a computer, which uses these values to compute an appropriate adjustment of moveable mirror assembly 98 (FIG. 19) to achieve the desired alignment. It will be appreciated that the required adjustment can be calculated based on the known location of incidence of the signals and system geometry, by using basic geometric principles.

[0101] Referring again to FIG. 19, the lens assembly 92 receives incoming signals (via window 102, mirror assembly 98, and mirror 94) and focuses the signals on fiber 106. The lens assembly 92 also receives outgoing signals from fiber 106 and transmits such signals in a focused beam through window 102 via mirror 94 and mirror assembly 98. The lens assembly 92 can be an appropriate lens doublet or triplet for providing the desired optical performance. In this regard, only on-axis performance is required due to the optical geometry of the system. It will be appreciated that the optical arrangement of the illustrated embodiment allows for construction of very large switches, e.g., 1000×1000 or larger, as the optical configuration directs signals on-axis into the lens despite large transmission angles (relative to the lens axis) within the switch interface.

[0102] Mirror 94 is provided primarily for optical path folding and any appropriate mirror may be used in this regard. RED 96 is mounted on a circuit board 128 for providing the proper power signals to control pulsing of the RED 96. A radiation detector 130 is also mounted on board 128 facing the REDs 100 mounted on assembly 98. This detector 130 measures the amount of radiation emitted by the REDs for calibration and maintenance purposes.

[0103] FIG. 19 generally shows that the transmitted signal is collected by lens assembly 92 to form a beam for transmission across the switch interface. In order to reduce optical losses, the transmitted beam is preferably a focused beam as opposed to, for example, a collimated beam (composed of substantially parallel rays). Such focusing optics are illustrated in FIGS. 30A-30B. For ease of illustration, folding optics and moveable mirrors (or other beam directing elements) are omitted. As shown in FIG. 30A, signals from first end 400 of first optical fiber 402 are imaged by first focusing optics 404 substantially on a surface of second focusing optics 406 thus defining a first focused beam 405. Second focusing optics 406 receives the first focused beam 405 and distributes the signal across end 408 of second optical fiber 410. Similarly, as shown in FIG. 30B, signals from second fiber end 408 are imaged by second focusing optics substantially on a surface of first focusing optics 404 thus defining a second focused beam 407. First focusing optics receives the second focused beam 407 and distributes the signal across end 400 of first fiber 402. Such focusing ensures that optical losses are minimized and optical efficiency is enhanced.

[0104] Generally, such focusing is a function of the positioning of the optics 404 and 406 relative to the fiber ends 400 and 408 (as defined by distances u and v), the effective aperture of the fibers 402 and 410, the effective aperture(s) of the optics (D) the numerical aperture (NA) of the fibers and the focal length(s) (f) of the optics. More particularly, optical efficiency can be optimized by arranging the optics to satisfy the following three equations:

[0105] D=2utan(sin⁻¹(NA))+d

[0106] 1/f=1/v+1/u

[0107] d/u=D/v

[0108] NA is defined as the sin of the fiber emitting angle α. A thin lens approximation is assumed, and D>>d is also assumed. For the purposes of these equations, in the case that the beam is a Gaussian beam, the effective values of d, D and NA are determined on a 1/e²basis.

[0109] This may be better understood by reference to FIGS. 51-53. FIG. 51 is a cross sectional view of a fiber 1200. The fiber includes a core 1202 for carrying optical signals surrounded by cladding 1204. In order to efficiently transmit optical signals along the length of the fiber 1200, it is desirable to provide a high degree of reflectivity at the core/cladding interface 1206, e.g., by forming the core 1202 and cladding from materials having differing indices of refraction or otherwise providing a reflective coating. As shown in FIG. 51, the illustrated interface 1206 has a critical angle such that optical rays 1208 having an angle of incidence less than the critical angle are transmitted through the core 1202 and rays 1210 having an angle of incidence greater than the critical angle are not transmitted through the core 1202. This critical angle defines the “acceptance” angle of the fiber 1200, α, which defines the fiber's numerical aperture.

[0110] FIG. 52 shows the fiber 1200 and lens 1212 geometry. As shown, an effective diameter, D, of the lens 1212 is defined by the diameter, d, of the fiber core 1202 and the numerical aperture NA.

[0111] Specifically, as noted above:

[0112] D=2utan(sin⁻¹(NA))+d

[0113] Physically, this means that signals transmitted from the fiber 1200 will pass within the area defined by D. Conversely, incoming optical signals that are substantially aligned with the fiber axis and passing within the area defined by D will be substantially accepted by the fiber 1200.

[0114] Referring to FIG. 53, an imaging geometry in accordance with the present invention is shown. For purposes of illustration, a straight (unfolded) optical path connecting first and second fibers is shown and the beam directing units are omitted. As described above, the first beam forming unit 1300 preferably images the core 1302 of first fiber 1304 onto the effective diameter D₂of second beam directing unit 1306. Similarly, the second beam directing unit 1306 preferably images the core 1308 of second fiber 1310 onto the effective diameter D₁of the first beam forming unit 1300. It will be appreciated that, in the case of an NXN switch, the length of the optical path between the beam forming units may vary somewhat depending upon the particular connection. However, substantial imaging can be achieved for all connections provided that the variation of v from path to path minimized, preferably to less than about 10%. This can be achieved, for example, by increasing the magnitude of v relative to the dimension of the fiber arrays. Where folded optical paths are employed substantial imaging can be achieved in reasonably compact switches.

[0115] As shown in FIG. 53, the illustrated imaging relationship defines an optical path between the fibers 1304 and 1310 substantially bounded by boundaries 1312 and 1314. FIG. 53 also shows a control signal source 1316 and a control signal detector 1318 in accordance with an “on-axis” configuration of the present invention. As shown, the control signals are transmitted “on-axis” between the control signal source 1316 and detector 1318 relative to the communications signal pathway in that control signal axis 1320 is disposed within the boundaries 1312 and 1314 between the control signal deflectors 1322 and 1324. In this regard, the illustrated source 1316 is optically disposed within the numerical aperture of the second beam directing unit 1306 relative to reflector 1324.

[0116] Returning to FIG. 19, the moveable mirror assembly 98 includes moveable mirror surfaces 132 with related control elements and REDs 100 mounted on a housing 134. The assembly 98 is used to actuate both targeting and alignment adjustments. The mirror surfaces 132 move in response to commands from processor 104 to allow for adjustment of the optical path of the communication and control signals received through window 102 in two dimensions relative to the fiber 106 and sensor unit 90. Any moveable mirror unit with appropriate two-dimensional adjustability, response rate and command input interfaces may be employed in this regard. The illustrated assembly employs a chip mounted, micro electro mechanical (MEM) mirror such as manufactured by Texas Instruments.

[0117] FIG. 25 shows such a chip mounted moveable mirror assembly 98. As shown, the assembly 98 includes a mirror surface 132 and alignment REDs 100 mounted on a chip 150. The mirror surface 132 is supported on a gimbal mechanism that provides two degrees of freedom. In particular, two axially aligned flexible hinges 152 allow the mirror to pivot about a first axis 154. The hinges 152 and axis 154, in turn, are supported within a plane defined by rigid frame 156. The frame 156 is interconnected to the chip 150 via two aligned flexible hinges 158 that allow the mirror surface to pivot about a second axis 160. This gimbal mechanism, which may be fabricated in one part from silicon, thereby provides two degrees of freedom for targeting and alignment. In this regard, the mirror surface 132 and/or frame 156 are designed to respond to changes in an electromagnetic field so as to pivot in a known manner based on local field changes. Such field changes are controlled by providing appropriate signals, e.g., currents, to chip mounted electromagnetic elements adjacent to the mirror surface 132 and frame 156.

[0118] It will be appreciated that, instead of providing one mirror that provides two dimensions of beam directing control, two or more movable mirrors could be utilized, e.g., two mirrors that each provide one-dimension of beam directing control. However, the illustrated one movable mirror embodiment may be preferred for certain applications as it allows for smaller mirrors. That is, in the case of two movable mirrors, the beam would move about the surface of at least one of the movable mirrors, due to movement of the other mirror, thereby requiring a larger mirror for minimum signal loss.

[0119] Referring to FIG. 19, the REDs 100 are mounted on housing 134 in known relation to the fiber 106 relative to the optical path, generally indicated at 136. In the illustrated embodiment the REDs 100 and RED 96 are near infrared emitting diodes, e.g., emitting radiation having a wavelength of 880 nm or 950 nm. Preferably, the REDs 96 and 100 associated with a particular fiber operate independently relative to the REDs of other fibers in the switch and are not dependent on a common system clock. Window 102, which is preferably substantially transparent to the communication and control signals, is provided to keep the unit clean. In this regard, the space within the chassis housing may be filled with clean dry air or dry nitrogen.

[0120] FIG. 26 is a flow chart illustrating the closed-loop servo targeting and alignment control process. The process involves receiving (162) a command from a network controller indicating that a given first side fiber line is to be connected to a given second side fiber line. It will be appreciated that such commands may be received on a relatively infrequent basis in comparison to the alignment control signals which are transmitted continuously. When a new target is indicated (163) based on switching commands, the moveable mirrors are operated to effect an open-loop jump (165) to the new target. The alignment and targeting REDs of the fibers to be aligned then continue operation as described above to transmit (164) targeting and alignment signals. The signals transmitted by each of the subject fibers are received (166) by the sensor(s) of the other subject fiber. Based on output signals from the sensors, a processor determines (168) information regarding a target code and incidence locations of the signals. For example, the output signals may indicate that the correct fibers are connected and are properly aligned for transmission of communications signals therebetween, or the output signals may indicate that the optical path is aligned to the right or left, or up or down, from the targeted fiber end. As described above, such information is readily derived based on the known spatial relationships between the REDs, the sensors and the fiber end.

[0121] Based on this information, the processor determines (170) whether a path correction is required to effect the desired connection or for proper alignment. If no correction is required then the alignment process is complete and the optical path is held (171) as is. If correction is required, the processor calculates (172) an appropriate corrective action based on knowledge of the system geometry. Such corrective action may involve, for example, bending a fiber end using a piezoelectric bender or moving a moveable mirror. The corrective action is implemented (174) by transmitting appropriate signals to the associated actuators and the control system continues to monitor switching commands to identify further switching processes. It will be appreciated that this alignment process is executed on a substantially real-time basis by components associated with both of the subject fiber lines. For enhanced accuracy, such alignment is monitored on a repeated or continuous basis, as generally indicated by feedback loop (178), to iteratively optimize alignment. This feedback loop may be repeated, for example, about 500 times per second and continues throughout operation of the switch. Once an acceptable connection has been made, communications signals may be effectively transmitted (176) between the subject lines.

[0122] FIGS. 20-22 show an implementation of the components illustrated in FIG. 19 in a specific switch embodiment. For ease of reference, corresponding components from FIG. 19 are identified by corresponding numerals in FIGS. 20-22. As shown in FIGS. 20 and 22, a control unit 138 for a particular fiber 106 or a pair of such control units, are mounted in a tray 140. These trays 140 can be inserted into openings 142 in a chassis 144. In the illustrated embodiment, the chassis 144 supports a mirror 146 such that the first side fibers and second side fibers are arranged in an interspersed or side-by-side configuration. It will be appreciated that this tray and chassis construction allows for removal of individual trays for repair and maintenance as required without unduly affecting network operation.

[0123] FIGS. 29A-29C are schematic diagrams illustrating a further chassis implementation in accordance with the present invention. As shown in FIG. 29A, the switch 310 includes a chassis 312 for receiving a number of trays 314. Each tray 314 supports two fibers 316 and a beam directing unit for each fiber as described above. More particularly, each tray supports an input fiber 316A and an output fiber 318B as well as chip mounted electronics 324 for controlling the movable mirrors, REDs and detectors associated with the two fibers. The electronics 324 are connected via lead 318A associated with a controller 320A, which may include a computer system, for providing switching instructions. For example, the controller 320A may be interconnected to a telecommunications network switch operator. A similar controller 320B (FIG. 29B) is connected to the electronics 324 via lead 318B. Each of the controllers 320A/320B controls both the transmit and receive elements, and dual controller 320A/320B are included for redundancy. The input and output fibers 316A and 316B are optically interconnected via mirror 320A. In order to allow replacement or servicing of the mirror 322A, a second mirror 322B may be provided for sliding in front of the mirror 322A as desired. Precise positioning of the mirrors 322A and 322B can be accomplished by providing slots in a chassis housing for maintaining the mirror positions. It will be appreciated that the servo-control systems of the present invention readily accommodate any optical adjustments required as a result of mirror substitution.

[0124] FIG. 31 shows a further alternative configuration of a beam directing unit that eliminates the use of a stationary mirror, thereby simplifying the design and possibly reducing optical losses. In the illustrated embodiment, received signals are transmitted by a moveable mirror 500 housed in mirror housing 502 to focusing lens 504 without any intervening mirrors. The focusing lens 504 focuses the received signals (on a wavelength dependent basis) on the end of fiber 506 or onto a detector 508 housed in detector housing 510 via dichroic beam splitter 512.

[0125] FIG. 32 shows a further alternative configuration of a beam directing unit that eliminates the need for a beam splitter. In particular, this configuration takes advantage of the wavelength transmission characteristics of silicon to interpose a control signal detector 600 in the communications signal path. Since silicon is substantially transparent to wavelengths above about 1200 nm, 1310 nm or 1550 nm (for example) communications signals are transmitted through the detector 600 to the core 608 of fiber 610 whereas control signals having wavelengths of, for example, 880 or 950 nm are absorbed and detected by detector 600. The detector 600 can be mounted on a ceramic substrate 602 using glue 604. Electrical connections are effected by bonding wires 606. The detector 600 can be bonded to fiber 610 by index matching glue 612.

[0126] FIG. 33 shows an embodiment similar to that of FIG. 32 with like items identified by corresponding numerals. In this case, however, the detector is etched to form a receptacle 614 for engaging the fiber 610, thereby facilitating accurate relative positioning of the fiber to the detector and is further etched to define a cavity 616. The cavity 616 reduces the thickness of the detector 600 for better spatial resolution with respect to the incoming, generally conical beam.

[0127] FIG. 34 shows one embodiment of an optical switch wherein an on-path control signal system is implemented for use in configuring the optical switch such that an optical communication signal (represented by the long-short dashed line 702) transmitted from a first fiber end 710A may be transmitted along a desired signal pathway (represented by the long-long dashed line 704) between the first fiber end 710A and a second fiber end 712A. The system employed is referred to as an “on-path control signal system” because a control signal (represented by the short-short dashed line 706) is transmitted on at least a portion of the same pathway over which the communication signal 702 is transmittable in the switch. Hence, the control signal 706 is “on-path” with the communication signal 702 (the on-path communication and control signals are represented by the continuous line 708). The pathway over which the communication signal is transmittable is referred to as the communication signal pathway (also identified by the continuous line 708 in FIG. 34). Although FIG. 34 may suggest that the communication and control signals 702, 706 are transmitted during the same temporal period, it should be appreciated that the control and communication signals 702, 706 may not be transmitted during the same temporal period. In fact, the control signal 706 may be transmitted prior to transmission of the communication signal 702 so that the switch may be appropriately configured before transmission of the communication signal 702.

[0128] In FIG. 34 the optical switch employing the on-path control scheme is a mirror based switch having first and second positionable mirrors 714, 716 that provide the desired pathway 704 between the first and second fiber ends 710A, 712A. For simplicity, only two fiber ends 710A, 712A and two mirrors 714, 716 are depicted. It should be appreciated that the mirror based switch may in general be an N×N switch having multiple positionable mirrors (which may be arranged in two or more arrays) for directing communication signals between a plurality of fibers. Furthermore, the on-path control signal system of the present invention is not restricted to mirror based switches and may be implemented in non-mirror based switches as well, such as is shown in FIG. 36 discussed below. Also, other elements that those skilled in the art will appreciate may be necessary for the operation of the switch, such as optical elements for focusing the communication signal 702, have not been shown for purposes of simplicity.

[0129] The control signal 706 may be generated and transmitted on-path with the communication signal pathway 708 in a number of manners. For example, as is shown in FIG. 34, a control signal transmitter 720 and a first optical element 722 may be associated with the first fiber end 710A. The transmitter 720 may be RED that is capable of transmitting a control signal 706 having a different wavelength than the communication signal 702. The first optical element 722 receives the communication signal 702 on a first entrance pathway and receives the control signal 706 on a second entrance pathway. The first optical element 722 transmits both the control signal 706 and the communication signal 702 on the same exit pathway (i.e. the communication signal pathway 708). The first optical element 722 may include a wavelength dependent mirror that permits transmission of the communication signal 702 therethrough but reflects the control signal 706, similar to the signal separator previously described in connection with FIGS. 11 and 12. It should be appreciated that the control signal 706 may also be transmitted with the communication signal 702 in the first fiber 710B, eliminating the need for the transmitter 720 and first optical element 722 within the optical switch. An example of such a configuration is shown in FIG. 35 discussed below.

[0130] A control signal detector 730 and second optical element 732 are associated with the second fiber end 712. The second optical element 732 receives the communication and control signals 708 on the same entrance pathway (i.e. the communication signal pathway 708). The second optical element 732 transmits the communication signal 702 on a first exit pathway towards the second fiber end 712A and the control signal 706 on a second exit pathway towards the detector 730. The second optical element 732 may include a wavelength dependent mirror that permits transmission of the communication signal 702 therethrough and reflects the control signal 708, such as previously described in connection with FIGS. 11 and 12.

[0131] When one or both of the mirrors 714, 716 are not properly oriented, the communication signal pathway 708 may not be coincident with the desired pathway 704 and the second optical element 732 will transmit the control and communication signals 706, 702 on exit pathways that deviate from the desired exit pathways. Such a case is depicted in FIG. 34 wherein the communication signal 702 does not enter the second fiber 712B and the control signal 706 is incident on the detector 730 at a location 734 that deviates from the location expected 736 when the communication signal pathway 708 is coincident with the desired pathway 704. The detector 730 is maintained in a known spatial relation relative the desired pathway 704 so that it may generate a feedback signal, based for example on the difference between the detected location 734 and the expected location 736 of incidence of the control signal 706 on the detector 730, that can be utilized to control the position of the mirrors 714, 716 in order to make the communication signal pathway 708 sufficiently coincident with the desired pathway 704. For example, the feedback signal from the detector 730 may be directed to a microprocessor that utilizes the feedback signal in generating appropriate signals for positioning the mirrors 714, 716 until the detected location 734 and expected location 736 sufficiently coincide. When the detected location 734 and the expected location 736 sufficiently coincide, the communication signal pathway 708 is sufficiently coincident with the desired pathway 704 and the communication signal 702 will be transmitted along the desired pathway 704.

[0132] Referring now to FIG. 35, the on-path control signal system is shown implemented in a mirror based switch without a first optical element and second optical element. Although only a 1×1 switch is shown for purposes of simplicity, it should be appreciated that the switch may in general be an N×N switch. In this implementation, a communication signal 802 and a control signal 806 having different wavelengths are both transmittable through a first fiber 810B by means outside of the optical switch. Thus, the control signal 806 exits the first fiber end 810A on-path with the communication signal pathway 808. A pair positionable mirrors 814, 816 direct the on-path communication and control signals 808 towards a second fiber end 812A. A wavelength dependent control signal detector 830, such as described previously in reference to FIGS. 32 and 33, associated with the second fiber end 812A is interposed in a desired pathway 804 adjacent to the second fiber end 812A. Due to its wavelength, the communication signal 802 is substantially transmittable through the detector 830. The control signal 806 has a wavelength such that it is detected by the detector 830. Based for example on the detected location of incidence 834 of the control signal 806 in comparison with the location of incidence expected 836 when communication signal pathway 808 is coincident with the desired pathway 804, the detector 830 generates a feedback signal that can be utilized in controlling the position of the mirrors 814, 816 in order to make the communication signal pathway 808 coincident with the desired pathway 804.

[0133] On-path control of bilateral communication signals between the first and second fiber ends 810A, 812A is also possible. A second wavelength dependent control signal detector 830′ may be associated with the first fiber end 810A and interposed in the desired pathway 804 adjacent to the first fiber end 810A. The second detector 830′ should have wavelength dependent transmission properties such that it permits transmission of a communication and control signal from the first fiber end 810A and a communication signal from the second fiber end 812A therethrough. However, a control signal transmitted from the second fiber end 812A having a wavelength different than the wavelengths of the two communication signals (bilateral communication signals may be of the same or differing wavelengths) and the other control signal should be detectable by the second detector 830′. In such an instance, the detector 830 associated with the second fiber end 812A should permit transmission of a communication signal and control signal from the second fiber end 812A and a communication signal from the first fiber end 810A therethrough, but it should detect a control signal from the first fiber end 810A.

[0134] The on-path control signal system is not restricted to implementation in a mirror based switch such as is shown in FIGS. 34 and 35. For example, FIG. 36 shows an implementation of the on-path control signal system in a switch that relies on pointing the fibers at one another in order to configure the switch for transmission of a communication signal 902 between a first fiber end 910A and a second fiber end 912A. A first optical element 922 associated with the first fiber end 910A receives the communication signal 902 on a first entrance pathway from the first fiber end 910A and a control signal 906 on a second entrance pathway from a control signal transmitter 920. The first optical element 922 transmits both the communication and control signals 902, 906 together on the same exit pathway (i.e. the communication signal pathway 908) towards a second fiber end 912A. A control signal detector 930 associated with the second fiber end 912A permits transmission of the communication signal 902 therethrough but detects the control signal 906. A feedback signal is generated by the detector 930 relating to the spatial relationship between the communication signal pathway 908 and a desired pathway 904 between the first fiber end 910A and the second fiber end 912A. The feedback signal can be utilized in appropriately translating a first unit 940 comprised by a portion of the first fiber 910B, the signal transmitter and the first optical element 922 (e.g. in the direction indicated by arrow 960) so that the communication signal pathway 908 becomes sufficiently coincident with the desired pathway 904. A second unit 950 comprised of a portion of the second fiber 912B and the control signal detector 930 may also be cooperatively translated with the first unit 940 based on the feedback signal in order to make the communication signal pathway sufficiently coincident with the desired pathway 904, and hence make the communication signal 902 transmittable over the desired pathway 904.

[0135] By including a second control signal transmitter 920′ and a second first optical element 922′ in the second unit 950 and a second control signal detector 930′ in the first unit 940, on-path control of bilateral communication signals may be implemented. The first optical elements 922, 922′ and the control signal detectors 930, 930′ must have appropriate wavelength dependent properties. The first optical elements 922, 922′ and detectors 930, 930′ must permit transmission of communication signals therethrough in both directions. The detector 930 of the first unit 940 must permit transmission of a control signal from the signal transmitter 920 of the first unit 940 therethrough but detect a control signal from the signal transmitter 920′ of the second unit 950. The detector 930′ of the second unit must similarly permit transmission of a control signal from the control signal transmitter 920′ of the second unit 950 therethrough but detect a control signal from the control signal transmitter 920 of the first unit 940. Thus, it will be appreciated that the two transmitters 920, 920′ should be configured for transmitting control signals having differing wavelengths.

[0136] FIG. 37 shows one embodiment of a mirror based optical switch wherein an off-path control signal system is implemented for use in configuring the optical switch such that an optical communication signal (represented by the long-short dashed line 1002) may be transmitted on a desired signal pathway (represented by the long-long dashed line 1004) between a first fiber end 1010A and a second fiber end 1012A. The system employed is referred to as an “off-path control signal system” because a control signal (represented by the short-short dashed line 1006) is transmitted on a control signal pathway (also represented by the short-short dashed line 1006) separate from the communication signal pathway (also represented by the long-short dashed line 1002) of the communication signal 1002. Hence, the control signal 1006 is “off-path” from the communication signal pathway 1002. In FIG. 37 the mirror based optical switch implementing the off-path control scheme has first and second positionable mirrors 1014, 1016 that configure the desired pathway 1004 between the first and second fiber ends 1010A, 1012A. For simplicity, only two fiber ends 1010A, 1012A and two mirrors 1014, 1016 are depicted, but it should be appreciated that the mirror based switch may in general be an N×N switch. It should also be appreciated that additional switch components, such as focusing optics, have not been shown for purposes of simplicity. Also, the communication and control signals 1002, 1006 may or may not be transmitted during the same temporal period.

[0137] The control signal 1006 may be generated and transmitted on the control signal pathway 1006 separate from the communication signal pathway 1002 in a number of manners. For example, a control signal transmitter 1020 and a first optical element 1022 may be associated with the first fiber end 1010A. The transmitter 1020 may be RED that is capable of transmitting a control signal 1006 having a different wavelength than the communication signal 1002. The first optical element 1022 may include a wavelength dependent mirror 1024 that permits transmission of the communication signal 1002 therethrough towards the first mirror 1014 but reflects the control signal 1006 on the control signal pathway 1006 towards the first mirror 1014. The control signal pathway 1006 has a known spatial relation relative to the communication signal pathway 1002 over which the communication signal 1002 is transmittable. For example, the control signal pathway 1006 may be substantially parallel with the communication signal pathway as is shown in FIG. 37.

[0138] A control signal detector 1030 and second optical element 1032 are associated with the second fiber end 1012A. The second optical element 1032 receives both the communication signal 1002 and the control signal 1006 on separate entrance pathways (i.e. the communication and control signal pathways 1002, 1006). A wavelength dependent mirror 1038 in the second optical element 1032 permits transmission of the communication signal 1002 on a first exit pathway towards the second fiber end 1012A but reflects the control signal 1006 on a second exit pathway towards the detector 1030. When one or both of the mirrors 1014, 1016 are not properly oriented, the communication signal pathway 1002 may not be adequately aligned with the desired pathway 1004. The control signal pathway 1006 will likewise not be aligned with a control pathway 1026 expected when the mirrors 1014, 1016 are oriented such that the communication signal pathway 1002 is aligned with the desired pathway 1004. Such a case is depicted in FIG. 37 wherein the communication signal 1002 does not enter the second fiber 1012B and the control signal 1006 is incident on the detector 1030 at a location 1034 that deviates from the location expected 1036 when the communication signal pathway 1002 is aligned with the desired pathway 1004. The detector 1030 is maintained in a known spatial relation relative the desired pathway 1004 so that it may generate a feedback signal, based for example on the difference between the detected location 1034 and the expected location 1036 of incidence of the control signal 1006 on the detector 1030, that can be utilized to control the position of the mirrors 1014, 1016 in order to make the communication signal pathway 1002 sufficiently coincident with the desired pathway 1004.

[0139] The components associated with a single fiber of an optical switch such as previously described in connection with FIG. 19 may be understood to comprise an individual optical unit. FIG. 38 shows a side view of a first optical unit 1110 shown interfaced with a similarly configured selected second optical unit 1110′ on the opposing side of a switch interface. Each optical unit 1110, 1110′ is associated with a separate fiber end 1116, 1116′ and includes a lens 1112, 1112′, a beam directing element 1120, 1120′, a targeting signal source 1124, 1124′, control signal sources 1128, 1128′, a first mirror 1132, 1132′, and a control signal detector 1134, 1134′. Some elements, such as a processor, window, or targeting signal detector, that may be included within the optical units 1110, 1110′ have not been shown for purposes of simplifying the illustration. As is illustrated in FIG. 39, each beam directing element 1120, 1120′ may include two mirrors 1122, one or both of which may be moveable.

[0140] A communication signal 1114 is switched from the fiber end 1116 associated with the first optical unit 1110 (i.e the input fiber) to the fiber end 1116′ associated with the second optical unit 1110′ (i.e. the desired output fiber) in the following manner. The lens 1112 of the first optical unit 1110 receives the communication signal 1114 from fiber end 1116 and forms the communication signal 1114 into a beam 1118. The beam directing element 1120 directs the beam 1118 towards the beam directing element 1120′ of the second optical unit 1110′. The targeting signal source 1124, located adjacent to the beam directing element 1120, transmits a targeting signal 1126 for use in searching for and finding the beam directing element 1120′ of the second optical unit 1110′ among a plurality of beam directing elements 1120″ of optical units associated with fibers other than the desired output fiber. The control signal sources 1128, located around the beam directing element 1120, transmit control signals 1130 for use in precise alignment of the beam 1118. The incoming beam 1118 from the first optical unit 1110 is directed by the beam directing element 1120′ of the second optical unit 1110′ to the lens 1112′. The lens 1112′ focuses the beam 1118 onto fiber end 1116′. The first mirror 1132′ separates the control signals 1130 from the communication signal 1114 and directs the control signals 1130 towards the control signal detector 1134′. In this regard, the first mirror 1132′ is dichroic, allowing communication signals, typically having wavelengths of 820, 850, 1310 or 1550 nm, to pass through the first mirror 1132′, but reflecting control signals, which may have wavelengths of 880, 950, or shorter than 750 nm.

[0141] Since the units 1110, 1110′ are symmetric, it should be appreciated that a communication signal 1114′ may also be switched from the fiber end 1116′ associated with the second optical unit 1110′ to the fiber end 1116 associated with the first optical unit 1110 in a similar fashion. The lens 1112′ of the second optical unit 1110′ receives the communication signal 1114′ from fiber end 1116′ and forms the communication signal 1114′ into a beam 1118′. The beam directing element 1120′ directs the beam 1118′ towards the beam directing element 1120 of the first optical unit 1110. The targeting signal source 1124′ transmits a targeting signal 1126′ for use in searching for and finding the first optical unit 1110. The control signal sources 1128′ transmit control signals 1130′ for use in precise alignment of the beam 1118′. The incoming beam 1118′ from the second optical unit 1110′ is directed by the beam directing element 1120 of the first optical unit 1110 to the lens 1112. The lens 1112 focuses the beam 1118′ onto fiber end 1116. The first mirror 1132, which is dichroic, separates the control signals 1130′ from the communication signal 1114′ and directs the control signals 1130′ towards the control signal detector 1134.

[0142] As may be appreciated, the control signals 1130, 1130′ transmitted by the control signal sources 1128, 1128′ do share common apertures 1142, 1142′ with the communication signals 1114, 1114′ due to the location of the control signal sources 1128, 1128′ around the periphery of the beam directing elements 1120, 1120′ in the optical units 1110, 1110′ illustrated in FIG. 38.

[0143] Referring now to FIGS. 40A, B, D, E, F, H, I, J, K and L differently configured sensor surfaces 1136 appropriate for the control signal detectors 1134, 1134′ of the optical units 1110, 1110′ of FIG. 38 are illustrated. In each of these configurations except 40K and L, the sensor surfaces 1136 include a plurality of partitioned sensor areas 1138. Due to the location of the control signal sources 1128, 1128′, the control signals 1130, 1130′ therefrom are focused into images 1140 around the optical axis. Images of a targeting LED (for cases where a separate targeting LED is employed) are shown in phantom. The configurations illustrated permit measurement of how far the beam directing elements 1120, 1120′ are from their intended targets and correction of the aim of the beam directing elements 1120, 1120′ in the required two degrees of freedom. With the exception of the configuration shown in FIG. 40B, separate detectors are used for sensing targeting signals 1126, 1126′. If the sensor surface 1136 is configured as shown in FIG. 40B, both the control signals 1130, 1130′ and the targeting signals 1126, 1126′ may be detected with a single detector.

[0144] In addition to the optical unit configuration previously described in connection with FIG. 38, other configurations are possible wherein the control signal sources and detectors are positioned differently. Examples of such configurations are illustrated in FIGS. 41-50. In each of FIGS. 41-50, only a single optical unit is shown, but it should be appreciated that such units are interfaceable with similarly configured units.

[0145] In FIG. 41, the control signal sources 1128 are arranged around the periphery of the lens 1112 rather than the beam directing element 1120. Since the control signal sources 1128 are arranged around the lens 1112, the control signal detector 1134 should have a sensor surface 1136 configured as in FIGS. 40A, B, D, E, F, H, I or J. The control signal sources 1128 may have a wide emission angle or a narrow emission angle, as is illustrated. For example, the control signal sources 1128 may be vertical cavity diode lasers with an emission angle of a few degrees. The use of control signal sources 1128 with a narrow emission angle is possible since, due to the location of the control signal sources 1128, the narrow control signal beam 1130 from each control signal source 1128 may be aimed by the beam directing element 1120 at another selected optical unit. The detector of the other optical unit may use the narrow control signal beams 1130 in aligning its own beam directing element. Since the configuration shown in FIG. 41 permits the use of narrow control signal beams 1130, a higher radiance beam 1118 is available and the control signals are stronger with improved signal to noise ratio. However, narrow control signal beams 1130 such as illustrated require the use of a targeting signal source 1124 when searching for the other optical unit, which may be aimed arbitrarily. Also, the beam directing element 1120 of FIG. 41 should have a larger clear aperture than the beam directing element 1120 of FIG. 38 in order to accommodate both the communication signal beam 1118 from the lens 1112 and the control signal beams 1130 emitted by the control signal sources 1128 arranged around the lens 1112. Two units 1110 configured as shown in FIG. 41 are interfaced for transmission of communication signals therebetween by first searching for the targeting signal source 1124 of the opposing unit and, after each unit is aimed in the general direction of one another, the control signals 1130 emitted by the control signal sources 1128 of the other unit are used for precise alignment. As may be appreciated, in the optical unit 1110 illustrated in FIG. 41, the control signals 1130 and communication signal 1114 have a common aperture 1142.

[0146] FIG. 42 shows an optical unit 1110 wherein a single control signal source 1128 and the control signal detector 1134 are both positioned generally on the optical axis using a second mirror 1150. In this configuration, the control signal 1130 and communication signal 1114 also have a common aperture 1142. In order to direct a control signal 1130′ from another unit to the control signal detector 1134 while permitting transmission of a control signal 1130 from the control signal source 1128 to the other unit, the second mirror 1150 may be partially transmitting and partially reflecting in the control signal wavelengths. For example, the second mirror 1150 may be fifty percent transmitting and fifty percent reflecting. It should be appreciated that in such a case, only twenty-five percent of a transmitted control signal from one unit will reach the detector of the other unit. Another possibility is for the second mirror 1150 to be dichroic and to transmit different wavelength control signals from opposing units. Regardless of whether the second mirror 1150 is partially transmitting/partially reflecting or dichroic, the sensor surface 1136 of the control signal detector 1134 may be configured as shown in FIGS. 40C or G since, due to the location of the control signal source 1128, the control signal 1130 is focused on the optical axis. The control signal source 1128 may have a wide or narrow emission angle since the lens 1112 focuses the control signal 1130, as well as the communication signal 1114, into a beam. It should be noted that there may be some benefit to positioning the control signal source 1128 somewhat out of focus so that the control signal beam is larger than the aperture of the beam directing element of the other unit. Locating the control signal source 1128 out-of-focus has the advantage that slight misalignment of the beam directing element 1120 of one unit will not substantially influence detection of the control signal 1130 by the control signal detector 1128 of the other unit and thus the servo system or other device controlling the beam directing element 1120 of the other unit may be operated independently. As with the optical unit 1110 of FIG. 41, a separate targeting signal source 1124 is used to generally aim two of the units at one another and then the control signal sources 1128 and detectors 1134 are used for precise alignment.

[0147] FIGS. 43 and 44 illustrate optical units 1110 without the second mirror 1150 included in the configuration shown in FIG. 43. In FIG. 43, a plurality of control signal sources 1128 are positioned around the control signal detector 1134. The control signal sources 1128 are preferably positioned slightly out of focus and, when positioned as shown, may block part of the control signal cone reaching the control signal detector 1134. In FIG. 44, a single control signal source 1128 is positioned on the optical axis between the first mirror 1132, which is dichroic, and the control signal detector 1134. It is important to note that the control signal source 1128 should be positioned and sized so that it does not block the entire control signal cone reaching the control signal detector 1134. In the case of the configuration shown in FIG. 44, the sensor surface 1136 of the control signal detector 1134 may be configured as shown in FIGS. 40C or G. In the configurations shown in both FIGS. 43 and 44, the control signal(s) 1130 and communication signal 1114 share a common aperture 1142.

[0148] FIGS. 45-48 illustrate variations of the optical unit 1110 shown in FIG. 42. The optical units 1110 in FIGS. 45-48 include first and second mirrors 1132, 1150. With the configurations shown in FIGS. 45-47, the first mirror 1132 is dichroic (i.e transmits communication signal 1114 wavelengths and reflects control signal 1130 wavelengths) and the second mirror 1150 transmits all the communication signal 1114 and half of the control signal 1130 and reflects half of the control signal 1130. In FIG. 48, the first mirror 1132 is again dichroic but the second mirror 1150 is fifty percent transmitting and fifty percent reflecting. The optical units 1110 of FIGS. 46, 47 and 48 also include a second lens 1160 for focusing the control signal 1130 from the control signal source 1128 into a beam. The optical unit 1110 of FIG. 47 further includes a third lens 1162 for focusing a control signal 1130′ from another unit onto the control signal detector 1134. In the optical unit 1110 of FIG. 48, the second lens 1160 also focuses the control signal from another unit onto the control signal detector 1134. In the configurations shown in FIGS. 45-48, the control signal 1130 and communication signal 1114 share a common aperture 1142.

[0149] FIGS. 49 and 50 show optical units 1110 configured similar to the optical units 1110 of FIGS. 38 and 41, respectively, but with the positions of the control signal sources 1128 and control signal detectors 1134 reversed. In FIG. 49, the control signal source 1128 is on the optical axis and a plurality of control signal detectors 1134 are disposed around the beam directing element 1120. In FIG. 50, the control signal source 1128 is on the optical axis and a plurality of control signal detectors 1134 are arranged around the periphery of the lens 1112. In both configurations, the control signal source 1128 may be positioned slightly out of focus or have extended size perpendicular to the optical axis. The optical units 1110 illustrated in FIGS. 49 and 50 are less preferable than the previously described configurations because servo control information generated by the control signal detectors of one unit is needed to control the beam directing element of another unit with which it is interfaced. Thus, a communication channel between the two interfaced units needs to be established to transfer the servo control information. In the configurations shown in both FIGS. 49 and 50, the control signal 1130 and communication signal 1114 share a common aperture 1142.

[0150] While various embodiments of the present invention have been described in detail, it is apparent that further modifications and adaptations of the invention will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention.