Coherent wavelength locking

Abstract

The embodiment of the invention relates to coherent wavelength locking. An optical communication device includes a laser, a transmitter (Tx), a receiver (Rx), and a device controller. The laser is configured to generate an optical carrier. The transmitter is configured to generate an optical Tx signal using the optical carrier and to transmit the optical Tx signal to a peer optical communication device. The receiver is configured to receive an optical Rx signal from a peer-to-peer optical communication device and to down-convert the optical Rx signal using an optical carrier. The device controller is configured to adjust a frequency of the laser to reduce a carrier frequency offset (CFO) between the received optical Rx signal and an optical carrier generated by the laser, including conditionally applying a series of frequency hops to the frequency of the laser according to a defined jitter sequence.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 539,742, filed September 21, 2023, the disclosure of which is incorporated herein by reference. Technical Field

[0003] The present disclosure relates generally to optical communication systems and, more particularly, to methods and systems for controlling optical carrier wavelength. Background Art

[0004] Receivers in coherent optical communication systems typically use a laser to generate a local oscillator (LO) carrier and use the LO carrier to downconvert the incoming optical signal for demodulation. However, a free-running laser is typically unable to maintain the frequency (wavelength) of the LO carrier with sufficient stability to achieve frequency locking. The laser frequency varies, for example, as a function of temperature and output power, and also drifts over the lifetime of the laser. One possible way to improve the frequency stability of a laser is to use an optical wavelength locker.

[0005] The above description is presented as a general overview of the relevant art in the field and should not be construed as an admission that any of the information it contains constitutes prior art with respect to the present patent application. Summary of the Invention

[0006] Embodiments described herein provide an optical communication device comprising a laser, a transmitter (Tx), a receiver (Rx), and a device controller. The laser is configured to generate an optical carrier. The transmitter is configured to use the optical carrier to generate an optical Tx signal and transmit the optical Tx signal to a peer optical communication device. The receiver is configured to receive the optical Rx signal from the peer optical communication device and down-convert the optical Rx signal using the optical carrier. The device controller is configured to adjust the frequency of the laser to reduce a carrier frequency offset (CFO) between the received optical Rx signal and the optical carrier generated by the laser, including conditionally applying a series of frequency jumps to the frequency of the laser according to a defined dither sequence.

[0007] In some embodiments, the device controller is configured to: (i) operate a CFO loop that adjusts the frequency of the laser to reduce the CFO when the CFO is within a defined CFO capture range, and (ii) apply a series of frequency hops when the CFO is outside the defined CFO capture range at least until the CFO falls within the defined CFO capture range.

[0008] In some embodiments, when the CFO loop is locked, the device controller is configured to receive a reception quality measurement from a peer optical communication device and, in response to the reception quality measurement, modify the CFO loop to improve a performance metric. In an example embodiment, the device controller is configured to reduce power consumption of the optical communication device by relaxing the CFO loop. In another embodiment, the device controller is configured to reduce an error rate in the peer optical communication device by tightening the CFO loop.

[0009] In the disclosed embodiment, the device controller includes (i) a digital signal processor (DSP) configured to measure CFO and operate a CFO loop, and (ii) a controller configured to apply a series of frequency hops to the frequency of the laser. In one embodiment, the device controller is configured to initiate the series of frequency hops in response to detecting (i) an optical Tx signal being enabled at the Tx and (ii) a received optical Rx signal being present at the Rx.

[0010] In another embodiment, the device controller is configured to adjust the frequency of the laser by controlling a thermoelectric cooler (TEC) coupled to the laser and apply a series of frequency hops to the frequency of the laser. In yet another embodiment, the device controller is configured to apply the series of frequency hops according to a pseudo-random dithering sequence of positive and negative frequency hops.

[0011] According to embodiments described herein, a method for optical communication is also provided, comprising generating an optical carrier using a laser, generating an optical transmit (Tx) signal using the optical carrier, and transmitting the optical Tx signal to a peer optical communication device, receiving an optical receive (Rx) signal from the peer optical communication device, down-converting the optical Rx signal using the optical carrier, and adjusting a frequency of the laser to reduce a carrier frequency offset (CFO) between the received optical Rx signal and the optical carrier generated by the laser, including conditionally applying a series of frequency hops to the frequency of the laser according to a defined dither sequence.

[0012] The present disclosure will be more fully understood from the following detailed description of the embodiments of the present disclosure in conjunction with the accompanying drawings: BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a block diagram schematically illustrating an optical communication system including an optical communication device employing coherent wavelength locking according to embodiments described herein; and

[0014] Figure 2 is a schematic diagram of a method for performing a Figure 1 Flowchart of a method for performing coherent wavelength locking in an optical communication device. DETAILED DESCRIPTION

[0015] Embodiments described herein provide improved techniques for wavelength locking in optical communication systems.The terms "wavelength" and "frequency" are used interchangeably in this disclosure.

[0016] In some embodiments, an optical communication system includes optical communication devices that communicate with each other via a pair of optical fibers. Each optical communication device includes a laser, a transmitter (Tx), and a receiver (Rx). The laser generates an optical carrier used for transmission and reception. The transmitter uses the optical carrier to generate an optical Tx signal and transmits the optical Tx signal to a peer optical communication device. The receiver receives the optical Rx signal from the peer optical communication device and down-converts the optical Rx signal using the optical carrier as a local oscillator (LO).

[0017] Each optical communication device also includes a device controller that, among other tasks, is responsible for frequency locking. The device controller can include a single processor or multiple processors, such as a digital signal processor (DSP) and a microcontroller. In this context, the term "frequency locking" means matching the frequency of the laser (i.e., the LO frequency) to the frequency of the received optical Rx signal with sufficient accuracy to achieve successful demodulation of the optical Rx signal.

[0018] In one embodiment, the device controller operates a carrier frequency offset (CFO) loop that adjusts the frequency of the laser to reduce the CFO between the received optical Rx signal and the optical carrier generated by the laser. The CFO loop may include, for example, a proportional-integral-derivative (PID) loop or any other suitable control loop.

[0019] The CFO loop has a limited capture range (also called "acquisition range"). In this context, the term "capture range" is defined as the maximum offset between the wavelength of the received optical Rx signal and the wavelength of the optical carrier that the device controller can reliably measure (e.g., at least with a predefined reliability or quality level). If the initial CFO is within the capture range, the CFO loop will operate reliably and minimize the CFO. If the initial CFO is outside the capture range, the CFO loop will likely fail. For example, large CFO values ​​may occur during the initial setup of communications between optical communication devices.

[0020] In practical implementations, uncontrolled frequency variations of the laser (e.g., with temperature, voltage, and aging) do not guarantee that the initial CFO (e.g., at link setup) will fall within the capture range of the CFO loop. In principle, an optical wavelength locker can be used to reduce the frequency variation of the laser. However, this solution is very expensive and therefore prohibitive in some applications.

[0021] In some embodiments described herein, the device controller of the optical communication device further executes a "blind search" process to bring the initial CFO into the acquisition range of the CFO loop. The blind search process is typically performed at the beginning of the initial setup of a link between the optical communication devices. At this point in time, the optical communication device is completely out of sync with the peer device in terms of laser frequency.

[0022] In one embodiment, during a blind search process, the device controller begins applying a defined series of frequency hops to the laser's frequency. This series of frequency hops is referred to as a "dither sequence." The dither sequence is typically defined so that each optical communication device can run the blind search process independently of its peers, yet still guarantee that the CFO falls within the acquisition range after a short period of time. In one embodiment, the dither sequence includes a pseudo-random sequence of positive and negative frequency hops.

[0023] In some embodiments, optical communication devices synchronize the start of a blind search process with each other, even if they operate independently. In an example implementation, each optical communication device enables its transmitter and then checks its receiver for the presence of a received optical signal. An optical communication device begins the blind search process when (i) its transmitter is enabled and (ii) its receiver senses a received optical signal. In this way, both devices begin the blind search process simultaneously, even if they are unable to communicate with each other at that point in time.

[0024] During the application of the dither sequence, for example, after each frequency jump, the device controller checks whether the CFO is within the acquisition range. If so, the device controller terminates the blind search process and starts the CFO loop.

[0025] The disclosed technology provides a simple and effective wavelength locking solution, eliminating the need for expensive wavelength lockers. Furthermore, the disclosed technology enables the use of simpler and lower-cost lasers. Consequently, the cost of optical links using this technology can be significantly lower than traditional optical links. The disclosed optical links are suitable for use, for example, in short-distance network applications (such as within a data center), long-distance optical links connecting data centers, and a variety of other applications.

[0026] Figure 1 FIG2 is a block diagram schematically illustrating an optical communication system 20 according to an embodiment described herein, including optical communication devices 24A and 24B that employ coherent wavelength locking. Optical communication devices 24A and 24B communicate with each other via a pair of optical fibers 28A and 28B. Optical fiber 28A is used for communication from device 24A to device 24B. Optical fiber 28B is used for communication in the opposite direction, from device 24B to device 24A.

[0027] The bottom portion of the figure details the internal structure of an optical communication device (e.g., device 24A or 24B). Typically, both devices 24A and 24B have this internal configuration. In this example, device 24 includes a laser 32, a transmitter (Tx) 36 (also known as a modulator), a coherent receiver (Rx) 40, and a device controller 44. Device controller 44 includes a digital signal processor (DSP) 48 and a controller 52.

[0028] Laser 32 generates an optical carrier wave. The optical signal is used by transmitter 36 and receiver 40.

[0029] The transmitter 36 receives data to be transmitted (TxData) from the DSP 48 and modulates the data onto an optical carrier to generate an optical Tx signal. The optical Tx signal is transmitted to an optical fiber that is used for transmission to a peer optical communication device.

[0030] Receiver 40 receives the optical Rx signal via the optical fiber used for reception from the peer optical communication device. Receiver 36 mixes the optical Rx signal with the optical carrier generated by laser 32, i.e., uses the optical carrier as the LO. The resulting down-converted signal is designated as RxData. The RxData signal is provided to DSP 48 for demodulation.

[0031] In some embodiments, the device controller 44 (in this example, the DSP 48 and the controller 52) runs a CFO loop (e.g., a PID loop) that aligns the frequency of the laser 32 (i.e., the frequency of the optical carrier, the LO frequency) with the frequency of the optical Rx signal received by the receiver 40. In one embodiment, the DSP 48 measures the actual CFO (the frequency difference between the optical carrier and the optical Rx signal) by analyzing the RxData signal. The DSP 48 sends a digital signal labeled CFOMon to the controller 52, which indicates the measured CFO. The controller 52 adjusts the laser frequency to minimize the CFO.

[0032] In one embodiment, controller 52 controls the frequency of laser 32 by controlling the temperature of a thermoelectric cooler (TEC) 56 that is thermally coupled to laser 32. The signal that controls the TEC is labeled "FreqCtrl." In alternative embodiments, controller 52 may use any other suitable mechanism to control the frequency of laser 32.

[0033] As noted above, the CFO loop of the device controller 44 has a somewhat limited capture range. If the CFO is outside the capture range, the DSP 48 will not be able to measure the CFO, and the CFO loop will not converge. In practice, frequency variations of the laser 32 (which vary with temperature, voltage, and aging) may cause the laser frequency to fall outside the capture range of the CFO loop. In the exemplary embodiment, the DSP 48 is able to measure the CFO as long as the CFO does not exceed ±20 GHz. On the other hand, the laser frequency may vary by ±15-20 GHz or more. In this example, the actual CFO may exceed the capture range of the CFO loop at margins in the operating conditions of the laser.

[0034] In some embodiments, the controller 52 includes a frequency hopping module 58 that conditionally executes a "blind search" process to bring the laser frequency into the CFO loop acquisition range. In the embodiments described herein, the blind search process is performed when a link is initially established between the optical communication devices 24A and 24B. At this stage, the frequency offset between the lasers of the two optical communication devices is unknown and cannot be assumed to fall within the acquisition range of the devices' CFO loops.

[0035] More generally, in response to various conditions, the frequency hopping module 58 in devices 24A and / or 24B may decide to conditionally initiate a blind search process. The conditions requiring initiation of the blind search process may include, for example, an interruption of the link between devices 24A and 24B, such as due to a fiber break, protection switching, or a reset.

[0036] In one embodiment, the frequency hopping module 58 begins the blind search process by applying a defined series of frequency hops to the frequency of the laser. This series of frequency hops is referred to as a "dither sequence."

[0037] The dither sequence is generally defined so that the optical communication devices 24A and 24B can run a blind search process independently of each other, but still guarantee that the CFO falls within the acquisition range (in both devices 24A and 24B) after a short period of time.

[0038] In one embodiment, the dithering sequence includes a pseudo-random sequence of positive and negative frequency jumps. The typical size of the frequency jumps in the sequence is approximately ±2 GHz. The typical duration of the frequency jumps in the sequence is approximately 100 ms. In some embodiments, the jumps in the sequence are of equal size (equal frequency step size). In other embodiments, the jump sizes in the sequence can vary; for example, the jump size (frequency step size) can increase gradually. As a result, the laser frequency jumps in a "random walk" manner, also known as a "drunkard's walk."

[0039] Frequency hopping module 58 typically limits the laser frequency to a defined frequency range (e.g., ±20 GHz, or any other suitable range). If the next pseudo-random hop in the sequence falls outside the defined frequency range, module 58 reverses the direction of the hop or otherwise maintains the laser frequency within the range.

[0040] As noted above, in this example, the controller 52 controls the frequency of the laser 32 by controlling the temperature of the TEC 56. In practice, the controller 52 may not typically have perfect knowledge of how to calculate the frequency of the laser 32 based on the temperature of the TEC 56. In some embodiments, the relationship between the TEC temperature and the laser frequency is calibrated as part of the production of the optical communication device 32. This process is sometimes referred to as "beginning of life" (BoL) calibration. Calibration information (e.g., a lookup table) specifying this relationship is stored in the controller 52 or in a memory accessible to the controller 52. The controller 52 uses the calibration information to determine the desired temperature of the TEC 56 at any given time. The disclosed blind search process does not require high-accuracy calibration—frequency errors of up to approximately ±2 GHz can typically be tolerated, and in some cases, even frequency errors of up to ±5 GHz can be tolerated.

[0041] In some embodiments, the device controllers 44 in the optical communication devices 24A and 24B synchronize the start of the blind search process between them so that both devices 24A and 24B will perform frequency hopping simultaneously. This synchronization is performed even though the devices 24A and 24B are unable to communicate with each other at this stage and each device has no information about the laser frequency of the peer device.

[0042] In one embodiment, the synchronization is based on the presence of a detection signal. In each optical communication device, the controller 52 (i) enables the transmitter 36 to transmit an optical Tx signal to the peer device, and (ii) checks whether the receiver 40 receives an optical Rx signal from the peer device. Figure 1 In the example of FIG, the controller 52 enables the transmitter 36 by asserting a control signal labeled “TxEnable.” The controller 52 checks for the presence of a received optical signal by checking for a control signal labeled “RxPwrMon” asserted by the receiver 40 .

[0043] Once both conditions are met (Tx is enabled and a receive signal is sensed), the frequency hopping module 58 begins a blind search process (i.e., begins a frequency hopping sequence). When each of the two device controllers 44 executes this process, the search process will begin approximately simultaneously in both devices 24A and 24B, even if the devices 24A and 24B cannot communicate with each other.

[0044] It should be noted that frequency hopping in a given optical communication device (24A or 24B) affects both the LO frequency (used for reception) and the frequency of the transmitted optical signal, since both use the same laser. As a result, the optical signal received in each device (24A or 24B) will also jitter as a result of jitter in the peer device. Therefore, during the blind search process, the lasers 32 in devices 24A and 24B will frequency hop relative to each other in a "random walk" manner.

[0045] At some point, the CFO in one of the devices will fall within the acquisition range of the CFO loop, causing that device to stop the blind search and open its CFO loop. As a result, the CFO in the peer device will also fall within the CFO loop acquisition range shortly thereafter. Therefore, both devices (24A and 24B) will end their blind searches and open their CFO loops at approximately the same time. At this stage, the receivers 40 in both devices will be able to demodulate their respective received signals and can begin normal communication.

[0046] As can be seen from the above description, the CFO loops of two optical communication devices (24A and 24B) may actively converge simultaneously at certain times. The CFO loop in one device affects the CFO loop in the peer device because the same laser 32 is used for both reception and transmission. CFO loop parameters (e.g., loop gain and bandwidth) should generally take this cross-coupling into account. For example, in one embodiment, the CFO loop gain is set to the highest gain (usually with a certain safety margin) that still meets the following conditions:

[0047] The peer CFO loop has enough time to lock.

[0048] When both CFO loops are actively converging, the CFO loop will not oscillate.

[0049] In some embodiments, after the blind search process is complete, the CFO loop is locked and normal communication is established between devices 24A and 24B, the device controllers 44 (e.g., DSPs 48) in the two devices can send information to each other via a management channel (also referred to as a "reverse channel"). The device controller 44 can use the information provided by its peer to optimize the frequency control of the laser 32. The optimization can be aimed at improving various performance indicators, such as bit error rate (BER) and / or power consumption. For example, various aspects of closed-loop control using a reverse channel can be found in U.S. Patents 10,382,125, 10,841,005, and 11,239,912.

[0050] The information sent over the reverse channel may include, for example, reception quality measurements such as CFO feedback information measured by DSP 48, BER, mean square error (MSE), analog-to-digital converter (ADC) fill (percentage of ADC codes actually used), or any other suitable information.

[0051] In various embodiments, the information received via the reverse channel can be utilized in various ways by the device controller 44. In one embodiment, when the received information indicates favorable conditions, the device controller 44 can relax control of the laser 32 and allow the laser to operate closer to its natural temperature. This relaxation can increase the CFO at the peer communication device, but can also reduce the power consumption of the TEC 56. As another example, the device controller 44 can optimize the BER at the peer communication device by more tightly controlling the frequency of the laser 32 (thereby more accurately centering the laser frequency within the passband of the transmitter and receiver filters). As yet another example, the device controller can relax the CFO loop to minimize power consumption, but only within a predefined BER threshold at the peer device. Alternatively, any other suitable optimization can be performed.

[0052] Figure 2 FIG2 is a flow chart schematically illustrating a method for coherent wavelength locking in optical communication devices 24A and 24B of system 20 according to an embodiment described herein. The flow chart illustrates the operation of one of the optical communication devices, referred to as "device 24" for clarity. As explained above, the two devices operate without explicit coordination, but their operations are implicitly synchronized by a signal sensing mechanism.

[0053] The method begins when the controller 52 of device 24 enables transmitter 36 in a Tx Enable phase 60. Transmitter 60 thereby begins transmitting an optical Tx signal. In a Receive Check phase 64, controller 52 checks whether receiver 40 senses an optical Rx signal. The method remains in Check phase 64 until receiver 40 notifies controller 52 of the presence of an optical Rx signal. Using this mechanism, and assuming that optical fibers 28A and 28B are connected simultaneously or before device 24 is initialized, device 24 will exit phase 64 at approximately the same time as its peer device 24.

[0054] In the CFO check phase 68, the controller 52 checks whether the CFO (measured by the DSP 48) is within the capture range of the CFO loop. If not, the frequency hopping module 58 in the controller 52 applies random frequency steps to the laser 32 in the dither phase 76. The method then loops back to phase 68. In this manner, the frequency hopping module 58 continues to apply random frequency dither steps to the laser 32 until the CFO falls within the capture range of the CFO loop.

[0055] As soon as the controller 52 detects (at stage 68) that the CFO falls within the acquisition range of the CFO loop, the frequency hopping module 58 stops the random dithering (blind search) process and turns on the CFO loop at the tracking stage 72. From this point on, the DSP 48 and the controller 52 adjust the laser frequency according to the CFO loop, aiming to minimize the CFO.

[0056] like Figure 1 The configuration of the system 20 and optical communication device 24 shown in FIG. Figure 2 The method flow is merely an example depicted for clarity. In alternative embodiments, any other suitable configuration and method flow may be used. For example, the above description describes a specific "division of labor," or task division, between the DSP 48 and the controller 52. In alternative embodiments, the device controller 44 may include one or more processors of any suitable type. When the device controller 44 includes two or more processors, various functions may be divided between the processors in any suitable manner. As another example, the disclosed technology may be applied to a system that uses a single optical fiber for bidirectional communication.

[0057] The various elements of the optical communication device 24 can be implemented using dedicated hardware or firmware, such as using hardwired or programmable logic, for example, implemented in an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA). Additionally or alternatively, some functions of the optical communication device 24, such as some or all functions of the DSP 48 and / or the controller 52, can be implemented in software and / or using a combination of hardware and software elements. For the sake of clarity, elements that are not necessary for understanding the disclosed technology have been omitted from the figure.

[0058] In some embodiments, some functions of the optical communication device 24, such as some or all functions of the DSP 48 and / or the controller 52, can be implemented in one or more programmable processors, such as one or more DSPs, central processing units (CPUs), or microcontrollers, that are programmed in software to perform the functions described herein. The software can be downloaded to any processor in electronic form, such as over a network, or it can alternatively or additionally be provided and / or stored on a non-transitory tangible medium, such as magnetic, optical, or electronic memory.

[0059] Although the embodiments described herein primarily address frequency locking in optical communication devices, the methods and systems described herein may also be used in other applications involving CFO measurements.

[0060] It should be noted that the above embodiments are cited by way of example, and the present invention is not limited to what is specifically shown and described above. On the contrary, the scope of the present invention includes combinations and sub-combinations of the various features described above, as well as variations and modifications that will occur to a person skilled in the art upon reading the above description and that are not disclosed in the prior art. The documents incorporated by reference in this patent application should be considered as an integral part of this application, but if the definition of any term in these incorporated documents conflicts with the definition explicitly or implicitly in this specification, only the definition in this specification should be considered.

Claims

1. An optical communication device comprising: a laser configured to generate an optical carrier; a transmitter Tx configured to generate an optical Tx signal using the optical carrier and transmit the optical Tx signal to a peer optical communication device; a receiver Rx configured to receive an optical Rx signal from the peer optical communication device and down-convert the optical Rx signal using the optical carrier; as well as A device controller is configured to adjust the frequency of the laser to reduce a carrier frequency offset (CFO) between the received optical Rx signal and the optical carrier generated by the laser, including conditionally applying a series of frequency hops to the frequency of the laser according to a defined dithering sequence.

2. The optical communication device of claim 1 , wherein the device controller is configured to: When the CFO is within a defined CFO capture range, operating a CFO loop that adjusts the frequency of the laser to reduce the CFO; and When the CFO is outside the defined CFO capture range, the series of frequency hops is applied at least until the CFO falls within the defined CFO capture range.

3. The optical communication device of claim 2, wherein when the CFO loop is locked, the device controller is configured to receive reception quality measurements from the peer optical communication device and to modify the CFO loop to improve a performance metric in response to the reception quality measurements. 4 . The optical communication device of claim 3 , wherein the device controller is configured to reduce power consumption of the optical communication device by relaxing the CFO loop. 5 . The optical communication device of claim 3 , wherein the device controller is configured to reduce an error rate in the peer optical communication device by tightening the CFO loop.

6. The optical communication device of claim 2, wherein the device controller comprises: a digital signal processor (DSP) configured to measure the CFO and operate the CFO loop; as well as A controller is configured to apply the series of frequency hops to the frequency of the laser.

7. The optical communication device of claim 1 , wherein the device controller is configured to initiate the series of frequency hops in response to detecting (i) the optical Tx signal being enabled at the Tx and (ii) the received optical Rx signal being present at the Rx.

8. The optical communication device of claim 1, wherein the device controller is configured to adjust the frequency of the laser and apply the series of frequency hops to the frequency of the laser by controlling a thermoelectric cooler (TEC) coupled to the laser.

9. The optical communication device of claim 1, wherein the device controller is configured to apply the series of frequency hops according to a pseudo-random dithering sequence of positive and negative frequency hops.

10. An optical communication method, comprising: generating an optical carrier wave using a laser; generating an optical transmission Tx signal using the optical carrier, and transmitting the optical Tx signal to a peer optical communication device; receiving an optical receive Rx signal from the peer optical communication device and down-converting the optical Rx signal using the optical carrier; as well as The frequency of the laser is adjusted to reduce a carrier frequency offset (CFO) between the received optical Rx signal and the optical carrier generated by the laser, comprising conditionally applying a series of frequency jumps to the frequency of the laser according to a defined dithering sequence.

11. The optical communication method of claim 10, wherein adjusting the frequency of the laser comprises: When the CFO is within a defined CFO capture range, operating a CFO loop that adjusts the frequency of the laser to reduce the CFO; as well as When the CFO is outside the defined CFO capture range, the series of frequency hops is applied at least until the CFO falls within the defined CFO capture range.

12. The optical communication method according to claim 11, wherein operating the CFO loop comprises: Reception quality measurements are received from the peer optical communication device when the CFO loop is locked, and the CFO loop is modified in response to the reception quality measurements to improve a performance metric.

13. The optical communication method of claim 12, wherein operating the CFO loop comprises: Power consumption is reduced by relaxing the CFO loop.

14. The optical communication method of claim 12, wherein operating the CFO loop comprises: The error rate in the peer optical communication device is reduced by tightening the CFO loop.

15. The optical communication method of claim 11, wherein adjusting the frequency of the laser comprises: Using a digital signal processor (DSP) to measure the CFO and operate the CFO loop; as well as The series of frequency hops is applied to the frequency of the laser using a controller.

16. The optical communication method of claim 10, wherein applying the series of frequency hops comprises: The series of frequency hops is initiated in response to detecting that (i) the optical Tx signal is enabled and (ii) the received optical Rx signal is present.

17. The optical communication method of claim 10, wherein adjusting the frequency of the laser and applying the series of frequency hops to the frequency of the laser comprises: Control the thermoelectric cooler TEC coupled to the laser.

18. The optical communication method of claim 10, wherein applying the series of frequency hops comprises: Applies a pseudo-random dithering sequence with positive and negative frequency hops.

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