Pump laser current driver

[0002] The present invention relates generally to lasers employed in optical transmission systems and, more particularly, to current drivers for powering lasers in optical transmission systems.

[0003] Pump lasers are conventionally used in many different types of optical transmission systems. In such systems, pump lasers may, for example, be employed in fiber amplifiers (e.g., Raman amplifiers or erbium-doped fiber amplifiers) for amplifying input optical signals. As shown in FIG. 1, a conventional pump laser system 100 may include a laser diode LD 105 that is driven by a current driver 110. Fixed supply voltage V_t115 further powers current driver 110. Inherent variations in the characteristics of each laser diode 105 used in pump laser system 100 can cause significant variations in the level of current and applied voltage that is required to produce a given optical output power.

[0004] Due to these inherent variations, the voltage level of fixed supply voltage V_t115 is conventionally selected based on the least possible efficient laser diode 105 that may be used in pump laser system 100. Thus, for any given laser diode 105 used in pump laser system 100, current driver 110 adjusts the laser diode voltage V_LD120 to produce the current i 125 required by the laser diode 105 to output a specific optical power. Since supply voltage V_t115 is fixed, the remaining voltage that is not dropped across laser diode 105 to produce the specific output power will be dropped across current driver 110. This voltage dropped across current driver 110 represents power that is wasted to produce a specific output power from laser diode 105. In practical laser systems, which may employ numerous laser diodes and associated current drivers, the multiplicative effect of this wasted power can be substantial, and may represent a significant portion of the power consumed by the overall system.

[0005] Therefore, there exists a need for systems and methods for reducing the quantity of power consumed by current drivers that drive optical transmission system laser diodes.

[0006] Systems and methods consistent with the present invention address this need and others by providing a current driver that includes current regulation circuitry for controlling each of the laser diodes of a series coupled laser diode pair. In one exemplary embodiment, at least one of the current regulators may increase or decrease the supply of current to one of the laser diodes by selectively diverting the current to a circuit path that may be connected in parallel to the respective laser diode. In other embodiments, one of the current regulators may adaptively control the voltage level of a power supply that powers both of the laser diodes. The power supply, thus, may supply only the minimum amount of voltage necessary to obtain a given optical output from the laser diodes. Operation of the current regulators, consistent with the present invention, advantageously serves to reduce the overall power consumed by the current driver as compared to conventional laser diode current drivers.

[0007] In accordance with the purpose of the invention as embodied and broadly described herein, a laser system includes first and second laser diodes coupled in series, and a power supply configured to adaptively adjust a voltage across the first and second laser diodes based on a current through at least one of the first and second laser diodes.

[0008] In another implementation consistent with the present invention, a laser system includes a power supply configured to supply current to a first laser diode, a first circuit path including the first laser diode, and a second circuit path configured to selectively divert current from the first circuit path to decrease the supply of current to the first laser diode.

[0009] In a further implementation consistent with the present invention, a laser system includes a series coupled laser diode pair, a first current regulator configured to control current supplied to the laser diode pair, a second current regulator configured to selectively divert a portion of the supplied current away from a first laser diode of the laser diode pair; and a power supply configured to adaptively adjust a level of a supply voltage applied across the series coupled laser diode pair.

[0010] In yet another implementation consistent with the present invention, a method of powering a laser system includes applying a supply voltage across first and second series coupled laser diodes, and adaptively adjusting a level of the supply voltage based on a current through at least one of the first and second laser diodes.

[0011] In a further implementation consistent with the present invention, a method of powering a laser system includes supplying a current to a first circuit path including a laser diode, and selectively diverting a portion of the current from the first circuit path to a second circuit path to decrease the current supplied to the laser diode.

[0012] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, explain the invention. In the drawings,

[0013] FIG. 1 illustrates a conventional pump laser system;

[0014] FIG. 2 illustrates an exemplary system in which systems and methods consistent with the present invention may be implemented;

[0015] FIG. 3 illustrates a first exemplary line unit consistent with the present invention;

[0016] FIG. 4 is a block diagram of a first exemplary current driver consistent with the present invention;

[0017] FIG. 5 illustrates exemplary components of the current driver of FIG. 4 consistent with the present invention;

[0018] FIG. 6 illustrates a second exemplary line unit consistent with the present invention;

[0019] FIG. 7 is a block diagram of a second exemplary current driver consistent with the present invention; and

[0020] FIG. 8 illustrates exemplary components of the current driver of FIG. 7 consistent with the present invention.

[0021] The following detailed description of the invention refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims.

[0022] Systems and methods consistent with the present invention provide mechanisms for reducing an overall power consumed by current drivers in optical transmission systems. Through adaptive control of a voltage level of the power supply that powers laser diodes in the system, a minimum amount of voltage necessary to obtain a given optical output from the laser diodes may be utilized.

[0023] FIG. 2 illustrates an exemplary system 200 in which systems and methods consistent with the present invention may be implemented. System 200 may include two land communication portions 205 that are interconnected via an underwater communication portion 210. The land portions 205 may include land networks 215 and land terminals 220. The underwater portion 210 may include line units 225 (sometimes referred to as “repeaters”) and an underwater network 230. Two land networks 215, land terminals 220, and line units 225 are illustrated for simplicity. System 200 may include more or fewer devices and networks than are illustrated in FIG. 2.

[0024] Land network 215 may include one or more networks of any type, including a Public Land Mobile Network (PLMN), Public Switched Telephone Network (PSTN), local area network (LAN), metropolitan area network (MAN), wide area network (WAN), Internet, or Intranet. The one or more PLMNs may further include packet-switched sub-networks, such as, for example, General Packet Radio Service (GPRS), Cellular Digital Packet Data (CDPD), and Mobile IP sub-networks. Land terminals 220 include devices that convert signals received from the land network 215 into optical signals for transmission to the line unit 225, and vice versa. The land terminals 220 may connect to the land network 215 via wired, wireless, or optical connections. In an implementation consistent with the present invention, the land terminals 220 connect to the line units 225 via an optical connection.

[0025] The land terminals 220 may include, for example, long reach transmitters/receivers that convert signals into an optical format for long haul transmission and convert underwater optical signals back into a format for transmission to the land network 215. The land terminals 220 may also include wave division multiplexers and optical conditioning units that multiplex and amplify optical signals prior to transmitting these signals to line units 225, and line current equipment that provides power to the line units 225 and underwater network 230.

[0026] The underwater network 230 may include groups of line units and/or other devices capable of amplifying and routing optical signals in an underwater environment. The line units 225 include devices capable of receiving optical signals and transmitting these signals to other line units 225 via the underwater network 230. The line units 225 may include wave division multiplexers and optical conditioning units that multiplex and amplify received optical signals prior to re-transmitting these signals via underwater network 230.

[0027] FIG. 3 illustrates a block diagram of a first exemplary line unit 225 consistent with the present invention. Line unit 225 may include a shunt regulator 305, a primary DC-DC converter 310, current drivers 315, and pump lasers 320. Shunt regulator 305 may regulate and shunt a portion of line current 330 to line unit 225. Primary DC-DC converter 310 may provide DC power to current drivers 315 and monitor control circuitry 325. Current drivers 315 may control the supply of voltage and current to pump lasers 320, consistent with the present invention, so as to reduce the power consumed by the current drivers. Pump lasers 320 provide an optical output 335 according to the current and voltage supplied by current drivers 315. Monitor and control circuitry 325 monitors the operation of the components of line unit 225.

[0028] FIG. 4 illustrates a block diagram of an exemplary current driver 315 consistent with the present invention. Current driver 315 may include current regulators 405 and 410 and secondary DC-DC converter 415. Current driver 335 adaptively supplies voltage V_tand current i to laser diode LD1420, resistor R1425, laser diode LD2430 and resistor R2435 of pump lasers 320. Current regulator 410 sets a nominal current through laser diodes LD1420 and LD2430 according to a voltage V₂dropped across resistor R2435. Current regulator 405 adjusts the current through laser diode LD1420 according to a voltage V₁dropped across resistor R1425. Current regulator 410 further supplies a control voltage, via resistor R3440, to adjust the DC-DC converter 415 output voltage V_tbased on the current supplied to laser diode LD2430. Operation of current regulators 405 and 410 is further described with respect to FIG. 5 below.

[0029] FIG. 5 illustrates exemplary components of current regulators 405 and 410 of current driver 315 according to an implementation consistent with the present invention. Current driver 315 includes voltage inputs V_MOD502 and V_SET504 that provide voltages to current regulators 405 and 410. Voltage input V_MOD502 provides the excitation voltage for modulating the current supplied to laser diodes LD1420 and LD2430 and, thus, modulating the laser diode optical output. Voltage input V_SET504 sets a nominal current through laser diodes LD1420 and LD2430. Values for V_SET504 can, for example, be received by line unit 225 from one of the land terminals 220, e.g., via a supervisory channel, to set the baseline output for a given laser diode. Likewise, values for V_MOD502 can be set to modulate the pump laser power in order to send information to the land terminals 220, e.g., in response to a command therefrom to measure the actual output laser power of a laser diode. Exemplary methods and systems for providing such supervisory signaling can be found in commonly-assigned, co-pending U.S. patent application Ser. No. 09/927,439, entitled “Redundant Line Unit Monitoring Architecture,” to John Mellert et al., filed on Aug. 13, 2001, the disclosure of which is incorporated herein by reference.

[0030] Voltages V_MOD502 and V_SET504, when applied to current regulator 410, can be divided across a divider network that includes resistors R_MOD506, R_SET508, and R4510. The output of the divider network may be applied to a controlled feedback amplifier that may include op-amp U1512, capacitor C1514, and resistor R5516. The output of the controlled feedback amplifier may control p-channel MOSFET transistor M3518, which in turn, can set a nominal current supplied by DC-DC converter 415 through the series connected laser diodes LD1420 and LD2430.

[0031] Voltages V_MOD502 and V_SET504 may, in current regulator 405, be applied to a series of amplifiers that control p and n-channel MOSFET transistors M1520 and M2522 based on feedback voltages measured at either side of resistor R1425. The series of amplifiers may include a first amplifier that includes op-amp U2524 and resistors R6526, R7528, and R8530; a second amplifier that includes op-amp U3532 and resistors R9534, R10536 and R11538; and a third amplifier that includes op-amp U4540, capacitors C2542 and C3544, and resistors R12546, R13548, R14550, and R15552. The output of the last amplifier of the series can be applied to the gates of transistors M1520 and M2522 to adjust the amount of current supplied to laser diode LD1420 by DC-DC converter 415. As either of the voltages V_MOD502 or V_SET504 increase (with the other voltage held constant), the output of the series of amplifiers will turn on transistor M1520 and turn off transistor M2522, thus, diverting current supplied by DC-DC converter 415 away from laser diode LD1420 through transistor M1520. As either of the voltages V_MOD502 or V_SET504 decrease (with the other voltage held constant), the output of the series of amplifiers will turn off transistor M1520 and turn on transistor M2522, thus, increasing the amount of current supplied to laser diode LD1420 by reducing the amount of current diverted through transistor M1520.

[0032] The output voltage V_tof DC-DC converter 415 may be controlled by the voltage on the source of transistor M3518 that is supplied via resistor R3440. DC-DC converter 415 may adjust the output voltage V_tbased on the voltage received via resistor R3440 and, thus, reduce the voltage dropped by current regulators 405 and 410 and decrease the overall power consumed by current driver 335.

[0033] FIG. 6 illustrates a block diagram of a second exemplary line unit 225 consistent with the present invention. Line unit 225 may include one or more laser modules (LM) 605a-605nthat may be interconnected with current balance circuitry 610. Current balance circuitry 610 may control the balancing of current supplied to each of the laser modules 605a-605n. Current balance circuitry 610 may further be connected to transient protection circuitry 615. A line voltage 620 may be connected across transient protection circuitry 615 and current balance circuitry 610 for supplying a line current 625 to power line unit 225. Transient protection circuitry 615 includes conventional circuitry for protecting line unit 225 from excessive transient voltages applied at line voltage 620.

[0034] Each laser module 605-605nmay include one or more adaptive voltage shunt regulators 630a-630n, one or more current drivers 635a-635n, pump lasers 640, and monitor and control circuitry 645. Shunt regulators 630a-630nmay supply an adaptive DC voltage to each of the current drivers 635a-635nand, thus, reduce the power consumed by the current drivers. Current drivers 635a-635nsupply current to pump lasers 640, consistent with the present invention, so as to control the current through the laser diodes of pump lasers 640. Pump lasers 640 provide an optical output 650 according to the current and voltage supplied by current drivers 635a-635n. Monitor and control circuitry 645 monitors the operation of the components of laser module 605.

[0035] FIG. 7 illustrates a block diagram of an exemplary current driver 635 consistent with the present invention. Current driver 635 may include current regulators 705 and 710 and adaptive shunt regulator 715. Current driver 635 controls the supply of current i to laser diode LD1720, resistor R1725, laser diode LD2730 and resistor R2735 of pump lasers 640. Current regulator 710 sets a nominal current through laser diode LD2730 according to a voltage V₂dropped across resistor R2735. Current regulator 705 sets a nominal current through resistor R1725 of pump lasers 640 according to a voltage V₁dropped across resistor R1725. Current regulators 705 and 710 further supply voltages, via resistors R3740 and R4745, to control adaptive shunt regulator 715. Adaptive shunt regulator 715 further adjusts the supply of current to laser diodes LD1720 and LD2730 and, thus, the voltages dropped across each of the respective laser diodes. Operation of current regulators 705 and 710 and adaptive shunt regulator 715 is further described with respect to FIG. 8 below.

[0036] FIG. 8 illustrates exemplary components of current regulators 705 and 710 and adaptive shunt regulator 715 of current driver 635 according to an implementation consistent with the present invention. Current driver 635 includes voltage inputs V_MOD502 and V_SET504 that provide voltages to current regulators 705 and 710. Voltage input V_MOD502 provides the excitation voltage for modulating the current supplied to laser diodes LD1720 and LD2730 and, thus, modulating the laser diode optical output. Voltage input V_SET504 sets a nominal current through laser diodes LD1720 and LD2730. Values for V_SET504 can, for example, be received by line unit 225 from one of the land terminals 220, e.g., via a supervisory channel, to set the baseline output for a given laser diode. Likewise, values for V_MOD502 can be set to modulate the pump laser power in order to send information to the land terminals 220, e.g., in response to a command therefrom to measure the actual output laser power of a laser diode. Exemplary methods and systems for providing such supervisory signaling can be found in commonly-assigned, co-pending U.S. patent application Ser. No. 09/927,439, entitled “Redundant Line Unit Monitoring Architecture,” to John Mellert et al., filed on Aug. 13, 2001, the disclosure of which is incorporated herein by reference.

[0037] Voltages V_MOD502 and V_SET504, when applied to current regulator 710, can be divided across a divider network that includes resistors R_MOD802, R_SET804, and R4806. The output of the divider network may be applied to a controlled feedback amplifier that may include op-amp U1808, capacitor C1810, and resistor R5812. The output of the controlled feedback amplifier may control p-channel MOSFET transistor M2814, which in turn, can set a nominal current level through laser diode LD2730.

[0038] Voltages V_MOD502 and V_SET504 may, in current regulator 705, be applied to a series of amplifiers that control p-channel MOSFET transistor M1842 based on feedback voltages measured at either side of resistor R1725. The series of amplifiers may include a first amplifier that includes op-amp U2822 and resistors R8816, R9818, and R10820; a second amplifier that includes op-amp U3830 and resistors R11826, R12824 and R13828; and a third amplifier that includes op-amp U4832, resistors R14834, R15836, R16838 and capacitor C2840. The output of the last amplifier of the series can be applied to the gate of transistor M1842 to set a nominal current level through laser diode LD1720.

[0039] As either of the voltages V_MOD502 or V_SET504 increase (with the other voltage held constant), the output of the series of amplifiers will turn on transistors M1842 and M2814, thus, increasing the current through laser diodes LD1720 and LD2730. As either of the voltages V_MOD502 or V_SET504 decrease (with the other voltage held constant), the output of the series of amplifiers will turn off transistors M1842 and M2814, thus, decreasing the current through laser diode LD1720 and LD2730.

[0040] Shunt regulator 715 may adaptively adjust the voltage supplied to current regulator 705. An amplifier, that may include op-amp U5844, resistor R17846, resistor R18850, and DC voltage V_DC1848, may control the conduction state of MOSFET M3852. DC voltage V_DC1848, in conjunction with resistors R17846 and resistor R18850, provides a reference voltage level to one input of op-amp U5844. Op-amp U5844 compares the voltage supplied via resistor R3720 to this reference voltage level. If the supplied voltage is greater than the reference voltage level, op-amp U5844 may turn MOSFET M3852 on, thus the voltage applied to current regulator 705 decreases. If the supplied voltage is less than the reference voltage level, op-amp U5844 may turn MOSFET M3852 off, thus, increasing the voltage supplied to current regulator 705.

[0041] Another amplifier, that may include op-amp U4860, resistor R19862, resistor R20866 and DC voltage V_DC2864, may further control the conduction state of MOSFET M4868. DC voltage VDC2854, in conjunction with resistors R19862 and resistor R20866, provide a reference voltage level to one input of op-amp U4860. Op-amp U4860 compares the voltage supplied via resistor R4745 to this reference voltage level. If the supplied voltage is greater than the reference voltage level, op-amp U4860 may turn MOSFET M4868 on, thus, reducing the voltage supplied to current regulator 710. If the supplied voltage is less than the reference voltage level, MOSFET M4868 may be turned off, thus, increasing the voltage supplied to current regulator 710.

[0042] Systems and methods consistent with the present invention provide mechanisms that can adjust the supply of current to at least one laser diode of a series coupled laser diode pair by selectively diverting the current to a circuit path that may be connected in parallel to the at least one laser diode. Systems and methods consistent with the present invention may further adaptively control the voltage level of a power supply that powers both of the series coupled laser diodes. The controlled power supply, thus, may supply only the minimum amount of voltage necessary to obtain a given optical output from the laser diodes. Overall power consumption of the current drivers driving the laser system laser diodes may, thus, be reduced.

[0043] The foregoing description of exemplary embodiments of the present invention provides illustration and description, but is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. For example, the exemplary current driver described above may be employed in any type of optical transmitter or amplifier that uses laser diodes, including, but not limited to, land terminal 220 shown in FIG. 2.

[0044] No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly described as such. Also, as used herein, the article “a” is intended to include one or more items. Where only one item is intended, the term “one” or similar language is used. The scope of the invention is defined by the following claims and their equivalents.