Dual-lensed unitary optical receiver assembly

[0001] This application claims the benefit of U.S. Provisional Application No. 60/876,848, filed Dec. 22, 2006 and U.S. Provisional Application No. 60/899,208 filed Feb. 3, 2007.

[0002] The present invention relates to a dual-lensed unitary optical receiver assembly and, more particularly, to a unitary assembly for providing passive alignment between an incoming optical fiber (or other waveguiding structure) and a photosensitive receiving device.

[0003] Optical networking, including fiber-optics and optoelectronics, is an important aspect of high speed communication systems, particularly for its ability to allow for efficient, accurate, and rapid transmission of data between various components in the network system. As with most communication systems, the efficient use of space and power in optical networks is of ever-increasing importance. Further, design considerations for such networks must take into account the modularity of the particular components that are included in the network.

[0004] Indeed, modular components are desirable in fiber optic systems to reduce the cost of manufacturing the system, which increases the more customized the system becomes. An example of a modular component is an optical receiver module, which may also be a portion of a complete optical transceiver assembly (including both an optical transmitter module and an optical receiver module), or an optical transponder further comprising wavelength multiplexing/demultiplexing. A typical optical receiver module includes an input port/channel for an optical fiber (or other light propagating arrangement), a photodiode for detecting the incoming optical signals, and a sensing circuit for converting the optical signals to digital electrical signals compatible with other network components.

[0005] The number and placement of these elements of an optical receiver has heretofore limited the ability to reduce the size of the receiver, as well as its cost and complexity. For example, optical alignment between an incoming optical signal (usually along an optical fiber) and a photosensitive device has typically required “active” alignment, with the placement of the photosensitive device being maneuvered until a maximum optical power is detected. In high speed optical receivers, the photosensitive device generally exhibits a relatively small active area (in order to more efficiently convert the optical signal into its electrical counterpart). This small active area makes the process of performing an active alignment even more difficult.

[0006] Thus, a need remains in the art for an optical receiver module that is truly compact and allows for the use of passive alignment between the incoming optical signal and the photosensitive receiving device.

[0007] The need remaining in the prior art is addressed by the present invention which relates to a dual-lensed unitary optical receiver assembly and, more particularly, to a transparent unitary assembly for providing passive alignment between an incoming optical fiber (or other waveguiding structure) and a photosensitive receiving device.

[0008] In accordance with the present invention, a unitary receiver assembly is formed to include a V-groove aligned with a collimating lens (the lens formed along a surface perpendicular to the V-groove). An optical fiber is disposed along the V-groove and is used to bring the received optical signal into the unitary assembly. Upon passing through the collimating lens, the received optical signal will intercept a turning mirror wall that directs the signal downward, through a focusing lens (also molded in the unitary assembly), and then into a photosensitive device. Advantageously, the photosensitive device is disposed in passive alignment with the focusing lens, allowing for a received signal to be coupled from an incoming optical fiber to a photosensitive device without needing any type of active alignment therebetween. The utilization of a focusing lens allows for a received signal to be efficiently coupled into the photosensitive device. Therefore, a small active area photodiode (as used in high speed applications) is suitable for use in the unitary module of the present invention. Moreover, by directly molding the collimating and focusing lenses (and V-groove) into the unitary receiver module, passive alignment between the fiber and photosensitive device is achieved, reducing the cost and complexity of the receiver arrangement.

[0009] In another aspect of the present invention, the unitary assembly may be formed to include an incoming optical waveguide (in place of an incoming optical fiber), where the core of the waveguide is again formed to be in alignment with the collimating lens.

[0010] It is a feature of the present invention that the use of molded lenses within the unitary assembly, in combination with the V-groove and turning mirror, allows for an array structure to be easily formed, accommodating a plurality of these features, disposed along the surface of a single assembly. Such an array of molded lenses may alternatively be used in association with an inserted prism element and single input fiber carrying multiple wavelength signals to form a demultiplexing device.

[0011] In prior art optical receiver/transceiver assemblies, the optical port axis is typically parallel to the supporting substrate surface. The assembly generally comprises two components: a TO can optical port assembly (containing a photodiode and a transimpedance amplifier), and a flex circuit for connecting the TO can to the substrate. The arrangement of the present invention eliminates the need for the two separate elements and particularly eliminates the need for the flex circuit inasmuch as the photodiode is directly located on the substrate as part of the unitary assembly.

[0012] Other and further aspects and features of the present invention will become apparent during the course of the following discussion and by reference to the accompanying drawings.

[0022] FIG. 1 illustrates an exemplary unitary optical receiver module 10 formed in accordance with the present invention. Module 10 is formed of a transparent material, such as a polyimide thermoplastic resin or any other material which allows for an optical signal to propagate therethrough with little or no loss of signal. An optical fiber 12, carrying the received optical signal, is disposed within a V-groove 14 formed in surface 16 of module 10.

[0023] A collimating lens 18 is molded along a vertical wall 20 so as to align with the core region of optical fiber 12. Collimating lens 18 functions to capture the optical signal exiting endface 22 of fiber 12 and form a collimated wavefront which thereafter propagates through the transparent material of module 10. As shown in FIG. 1, the propagating signal will intercept angled wall 24 of module 10, where wall 24 is beveled at a predetermined angle θ with respect to the optical axis (OA). In a preferred embodiment, the angle θ may be 45°, but other values may be used (with the properties of various other elements modified accordingly). The reflected signal will remain collimated, in this case now directed downward and into a focusing lens 26 molded along a horizontal wall 28 of module 10. A photosensitive device 30 (such as a PIN photodiode) is disposed underneath focusing lens 26 such that the optical signal entering lens 26 will be focused directly into the photosensitive region of device 30. As mentioned above, by using lens 26 to focus the light into device 30, a high speed, small active area photodiode may be used.

[0024] The isometric view of module 10 in FIG. 2 clearly illustrates the location and formation of V-groove 14 (while lenses 18 and 26 cannot be seen in this view). In this particular embodiment, V-groove 14 is shown as including an inner, shallower V-groove 14-1 for supporting an end section of bare fiber (i.e., fiber with the outer cladding removed) and an outer, deeper V-groove 14-2. Outer section 14-2 is used to support the incoming optical fiber which is still clad with an outer sheathing layer. Obviously, the details of the fiber-supporting V-groove are a matter of design choice (e.g., groove, trench, channel or the like, variously referred to hereinafter as “groove”), as long as the core region of the fiber will align with optical axis OA and the center of the first aspheric lens 18.

[0025] FIG. 3 is a ray tracing illustrating the various factors of concern to be considered when determining the dimensions of the molded, unitary receiver module of the present invention. These factors are shown as including: (1) the axis of the fiber; (2) the separation between the fiber endface and the collimating lens; (3) the axis of the photosensitive device; (4) the location of the turning wall at the intersection of the two axes (fiber and photosensitive device); and (5) the separation between the photosensitive device and the focusing lens. Of course, the curvature of the lenses will be factors involved in determining the separation between the lenses and their associated optical devices. It is an advantage of the present invention that the use of a molded structure to form module 10 allows for the curvature of each lens to be specifically tailored for its intended use, allowing for changes in curvature as the type of fiber and/or photodetector are changed.

[0026] Indeed, it is a specific advantage of the arrangement of the present invention that the ability to directly mold the lenses (and fiber/waveguide) into the receiver structure allows for a passively aligned receiver to be formed, eliminating the need for active alignment processes between the fiber, lenses and receiving device. The overall receiver is therefore less expensive and more efficient to manufacture than prior art receivers requiring active alignment. It has been found that today's precision molding capabilities allow for the lenses and V-groove (waveguide) to be formed and automatically aligned well within the acceptable tolerances associated with conventional optical receivers. FIG. 4 is a graph exemplary of this advantage, illustrating the acceptable tolerance range associated with the separation between the fiber endface and the collimating lens. As shown, a tolerance on the order of ±100 μm still yields an acceptable coupling efficiency (depicted as a reduction from 100% coupling efficiency) for a variety of different types of input fibers, including both multimode fiber and single mode fiber. FIG. 5 is another graph exemplifying this feature, in this case illustrating the tolerance associated with the separation between the focusing lens and the active area of the photosensitive device. As shown, a separation tolerance on the order of ±30 μm between the active area and the focusing lens still provides a sufficient coupling efficiency (again represented as a reduction from 100% coupling efficiency).

[0027] As mentioned above, a significant advantage of the unitary optical receiver module of the present invention is that it may be easily incorporated within a larger optical transceiver arrangement. FIG. 6 illustrates one such optical transceiver, with optical receiver module 10 used in association with an optical transmitter 30 and associated optical and electrical components 40 and 50, respectively.

[0028] Indeed, the utilization of a transparent, moldable material to form the optical receiver module of the present invention has been found to allow for an array structure to be formed, again eliminating the need to provide active alignment between the various components. FIG. 7 illustrates an exemplary unitary optical receiver array module 100, in this case used to support a set of five separate input signals. Each V-groove 14-1, 14-2, . . . , 14-5 is formed in a manner as discussed above to as to be in alignment with its counterpart collimating lens 18-1, 18-2, . . . , 18-5, respectively. A single beveled surface 24 provides the redirection for each of the signals into its own focusing lens (not shown in this view).

[0029] Instead of utilizing a plurality of separate input fibers, a unitary receiver array module of the present invention may utilize a single input fiber, carrying signals at multiple wavelengths and a prism to direct each different wavelength signal into a different collimating lens. FIG. 8 illustrates this embodiment in the form of a wavelength demultiplexing optical receiver module 200. Module 200 is shown as including a single V-groove 14 for supporting an incoming fiber (not shown), the fiber carrying a plurality of different signals operating at different wavelengths. A prism element 210 is disposed along trough 220 between V-groove 14 and vertical wall 20 supporting a plurality of separate collimating lenses 18-1, 18-2, . . . , 18-5. In this particular embodiment, prism 210 is configured to split apart the various received wavelengths, directing each wavelength toward a separate one of lenses 18. This is illustrated in FIG. 8 by a first wavelength signal λ₁ directed towards lens 18-1, a second signal at λ₂ directed toward lens 18-2, and so on.

[0030] While the principles of the invention have been described above in connection with the preferred embodiments, it is to be understood that this description is made only by way of example and not as a limitation on the scope of the invention.