Mitigating channel impairments with wavelength tuning

Abstract

An efficient structure and methodology are provided to mitigate channel impairments with wavelength tuning. A system can comprise a transmitter to generate an optical signal to a receiver via an optical fiber, where the optical signal has a wavelength, and a processor to control adjustment of the wavelength of the optical signal generated by the transmitter in response to feedback from the receiver regarding the optical signal.

Description

MITIGATING CHANNEL IMPAIRMENTS WITH WAVELENGTH TUNINGCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority to U.S. Provisional Application No. 63 / 713,507, filed on October 29, 2024, entitled “Mitigating Channel Impairments With Wavelength Tuning,” which provisional application is incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] The present disclosure is related to mitigating channel impairments and, in particular, to optical wavelength tuning.BACKGROUND

[0003] In the area of optical access, systems at 10 Gbit / s rate (e.g., XG-PON and XGS-PON) have been widely deployed. The InternationalTelecommunication Union Telecommunication Standardization Sector (ITU-T) has published the G.9804 series of recommendations, promoting 50 Gbit / s as the next generation of commercial optical access system. In 2023, the ITU-T started a new project G.sup.VHSP on passive optical network (PON) systems beyond 50G. G.sup.VHSP is an ITU-T project for developing the next-generation Very' High-Speed Passive Optical Network (VHSP) systems. There are also ongoing projects to specify optical access systems beyond 50 Gbit / s, and 200 Gbit / s is likely to be the future system rate. The increasing signaling rates are making optical channel impairments significant obstacles to transmission methods such as intensity modulation - direct modulation (IM-DD). Two major impairments include chromatic dispersion (CD) and polarization mode dispersion (PMD). Some designs build in enough margin so that the signal can still be received in the face of the worst case optical channel, that is, an open loop design with no adaptation. Other designs, such as HSP, have active equalization to adaptively compensate for channel impairments. There are limitations to this approach because IM-DD only recovers the optical power, missing the electric field phase information effectively discarding the phase information, which is critical formitigating these issues. Coherent communication can overcome this limitation, but at a significant cost.SUMMARY

[0004] It is an object of various embodiments to provide an efficient architecture and methodology for mitigating impairments in optical channels. By fine-tuning the optical wavelength of a transmitter that is transmitting an optical signal on an optical fiber, optical path impairments such as chromatic dispersion and polarization mode dispersion can be actively minimized, and overall system performance can be improved. The tuning of the wavelength can be based on data feedback to the transmitter node from a receiver node that is the target of the optical signal sent by the transmitter on the optical fiber. The data can be performance data on the transmitted optical fiber received at a receiver of the receiver node. Receiver feedback provides real-time performance monitoring. At the transmitter node, the data is evaluated and the wavelength of the optical signal being transmitted to the receiver can be adjusted.

[0005] According to a first aspect of the present disclosure, there is provided a system comprising a transmitter to generate an optical signal to a receiver via an optical fiber, the optical signal having a wavelength; and a processor to control adjustment of the wavelength of the optical signal generated by the transmitter in response to feedback from the receiver regarding the optical signal.

[0006] In a first implementation form of the system according to the first aspect as such, the processor is structured to continually monitor for feedback from the receiver and to adjust the wavelength of the optical signal generated by the transmitter based on monitoring the feedback.

[0007] In a second implementation form of the system according to the first aspect as such or any preceding implementation form of the first aspect, the processor is structured to control tuning of the wavelength of the optical signal, generated by the transmitter, based on a determination that signal degradation of the optical signal received by the receiver is larger than a threshold level of signal degradation.

[0008] In a third implementation form of the system according to the first aspect as such or any preceding implementation form of the first aspect, the processor is structured to control tuning of the wavelength of the optical signal.generated by the transmitter, based on an evaluation of signal impairment from data received in the feedback from the receiver.

[0009] In a fourth implementation form of the system according to the first aspect as such or any preceding implementation form of the first aspect, the data includes data associated with bit error rate of the optical signal generated by the transmitter.

[0010] In a fifth implementation form of the system according to the first aspect as such or any preceding implementation form of the first aspect, the processor is structured to control tuning of the wavelength of the optical signal, generated by the transmitter, based on identification of one optical signal of a set of multiple optical signals at different wavelengths being better than other optical signals of the set, the identification received in the feedback from the receiver.

[0011] In a sixth implementation form of the system according to the first aspect as such or any preceding implementation form of the first aspect, each optical signal of the set generated by the transmitter includes a timestamp different from timestamps of the other optical signals of the set; the feedback from the receiver includes a set of multiple feedback optical signals transmitted at different times; and one or more feedback optical signals of the set of multiple feedback optical signals includes a receiver timestamp for the respective feedback optical signal and the timestamp of the one optical signal of the set of multiple optical signals generated by the transmitter identified as being better than the other optical signals of the set of multiple optical signals generated by the transmitter.

[0012] In a seventh implementation form of the system according to the first aspect as such or any preceding implementation form of the first aspect, the transmitter continues to transmit the optical signal at the wavelength until evaluation of the feedback produces the adjustment.

[0013] In an eighth implementation form of the system according to the first aspect as such or any preceding implementation form of the first aspect, the system includes: the receiver in communication with the transmitter via the optical fiber, the receiver configured to receive the optical signal generated by the transmitter; a second processor coupled to the receiver at the receiver to evaluate the received optical signal control and generate data to be fed back tothe transmitter, the data associated with adjustment of the wavelength of the optical signal generated by the transmitter; and a second transmitter coupled to the second processor to transmit the generated data to the transmitter as the feedback from the receiver.

[0014] According to a second aspect of the present disclosure, there is provided a method comprising: generating an optical signal by and from a transmitter to a receiver via an optical fiber, the optical signal having a wavelength; and controlling, using a processor, adjustment of the wavelength of the optical signal generated by the transmitter in response to feedback from the receiver regarding the optical signal.

[0015] In a first implementation form of the method according to the second aspect as such, the method includes continually monitoring for the feedback from the receiver and adjusting the wavelength of the optical signal generated by the transmitter based on monitoring the feedback.

[0016] In a second implementation form of the method according to the second aspect as such or any preceding implementation form of the second aspect, the method includes controlling tuning of the wavelength of the optical signal, generated by the transmitter, based on a determination that signal degradation of the optical signal received by the receiver is larger than a threshold level of signal degradation.

[0017] In a third implementation form of the method according to the second aspect as such or any preceding implementation form of the second aspect, the method includes controlling tuning of the wavelength of the optical signal, generated by the transmitter, based on an evaluation of signal impairment from data received in the feedback from the receiver.

[0018] In a fourth implementation form of the method according to the second aspect as such or any preceding implementation form of the second aspect, the method includes generating the data to include data associated with bit error rate of the optical signal generated by the transmitter.

[0019] In a fifth implementation form of the method according to the second aspect as such or any preceding implementation form of the second aspect, the method includes: generating a set of multiple optical signals at different wavelengths, the set including the optical signal; identifying one optical signal of the set of multiple optical signals as being better than other optical signals of theset, identification of the one optical signal received in the feedback from the receiver; and controlling tuning of the wavelength of the optical signal, generated by the transmitter, based on the identification of the one optical signal of the set of multiple optical signals.

[0020] In a sixth implementation form of the method of according to the second aspect as such or any preceding implementation form of the second aspect, the method includes: incorporating in each optical signal of the set generated by the transmitter a timestamp different from timestamps of the other optical signals of the set; receiving a set of multiple feedback optical signals transmitted at different times as the feedback from the receiver, one or more feedback optical signals of the set of multiple feedback optical signals including a receiver timestamp for the respective feedback optical signal and the timestamp of the one optical signal of the set of multiple optical signals generated by the transmitter identified as being better than the other optical signals.

[0021] In a seventh implementation form of the method of according to the second aspect as such or any preceding implementation form of the second aspect, the method includes the transmitter continually transmitting the optical signal from the transmitter at the wavelength until evaluation of the feedback produces the adjustment.

[0022] In an eighth implementation form of the method of according to the second aspect as such or any preceding implementation form of the second aspect, evaluating, using a second processor coupled to the receiver at the receiver, the optical signal received by the receiver in communication with the transmitter via the optical fiber; generating, using the second processor, data to be fed back to the transmitter, the data associated with adjustment of the wavelength of the optical signal generated by the transmitter; and transmitting, using a second transmitter coupled to the second processor, the generated data to the transmitter as the feedback from the receiver.

[0023] According to a third aspect of the present disclosure, there is provided a non-transitory computer-readable storage medium storing instructions, wherein the instructions, when executed by one or more processors, cause the one or more processors to perform operations comprising generating an optical signal by and from a transmitter to a receiver via an optical fiber, the optical signalhaving a wavelength; and controlling, using a processor, adjustment of the wavelength of the optical signal generated by the transmitter in response to feedback from the receiver regarding the optical signal.

[0024] In a first implementation form of the non-transilory computer-readable storage medium according to the third aspect as such, the operations include continually monitoring for the feedback from the receiver and adjusting the wavelength of the optical signal generated by the transmitter based on monitoring the feedback.

[0025] In a second implementation form of the non-transitory computer- readable storage medium according to the third aspect as such or any preceding implementation form of the third aspect, the operations include controlling tuning of the wavelength of the optical signal, generated by the transmitter, based on a determination that signal degradation of the optical signal received by the receiver is larger than a threshold level of signal degradation.

[0026] In a third implementation form of the non-transitory computer-readable storage medium according to the third aspect as such or any preceding implementation form of the third aspect, the operations include controlling tuning of the wavelength of the optical signal, generated by the transmitter, based on an evaluation of signal impairment from data received in the feedback from the receiver.

[0027] In a fourth implementation form of the non-transitory computer- readable storage medium according to the third aspect as such or any preceding implementation form of the third aspect, the operations include generating the data to include data associated with bit error rate of the optical signal generated by the transmitter.

[0028] In a fifth implementation form of the non-transitory computer-readable storage medium according to the third aspect as such or any preceding implementation form of the third aspect, the operations include: generating a set of multiple optical signals at different wavelengths, the set including the optical signal; identifying one optical signal of the set of multiple optical signals as being better than other optical signals of the set, identification of the one optical signal received in the feedback from the receiver; and controlling tuning of the wavelength of the optical signal, generated by the transmitter, based on the identification of the one optical signal of the set of multiple optical signals.

[0029] In a sixth implementation form of the non-transitory computer-readable storage medium according to the third aspect as such or any preceding implementation form of the third aspect, the operations include: incorporating in each optical signal of the set generated by the transmitter a timestamp different from timestamps of the other optical signals of the set; receiving a set of multiple feedback optical signals transmitted at different times as the feedback from the receiver, one or more feedback optical signals of the set of multiple feedback optical signals including a receiver timestamp for the respective feedback optical signal and the timestamp of the one optical signal of the set of multiple optical signals generated by the transmitter identified as being better than the other optical signals.

[0030] In a seventh implementation form of the non-transitory computer- readable storage medium according to the third aspect as such or any preceding implementation form of the third aspect, the operations include the transmitter continually transmitting the optical signal from the transmitter at the wavelength until evaluation of the feedback produces the adjustment.

[0031] In an eighth implementation form of the non-transitory computer- readable storage medium according to the third aspect as such or any preceding implementation form of the third aspect, the operations include: evaluating, using a second processor coupled to the receiver at the receiver, the optical signal received by the receiver in communication with the transmitter via the optical fiber; generating, using the second processor, data to be fed back to the transmitter, the data associated with adjustment of the wavelength of the optical signal generated by the transmitter; and transmitting, using a second transmitter coupled to the second processor, the generated data to the transmitter as the feedback from the receiver.

[0032] In a ninth implementation form of the non-transitory computer-readable storage medium according to the third aspect as such or any preceding implementation form of the third aspect, the instructions, when executed by one or more processors, cause the one or more processors to perform operations to tune the wavelength of the optical signal transmitted by the transmitter to mitigate optical channel impairments of the optical fiber.

[0033] Any one of the foregoing examples may be combined wi th any one or more of the other foregoing examples to create anew embodiment in accordance with the present disclosure.BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.

[0035] Figure 1 represents an example closed-loop transmitter wavelength tuning control mechanism, according to various embodiments.

[0036] Figure 2 illustrates the principles of an example single-sided wavelength tuning control in a communication arrangement, according to various embodiments.

[0037] Figure 3 illustrates an example time-stamping feedback message arrangement, according to various embodiments.

[0038] Figure 4 is a diagram of an example apparatus that can implement channel impairment mitigation via wavelength tuning, according to various embodiments.

[0039] Figure 5 is a flow diagram of features of an example method of mitigating channel impairments via wavelength tuning, according to various embodiments.DETAILED DESCRIPTION

[0040] In the following description, reference is made to the accompanying drawings that form a part hereof, and in which is show n by way of illustration specific embodiments which may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments, and it is to be understood that other embodiments may be utilized, and that structural, logical, mechanical, and electrical changes may be made.The following description of example embodiments is, therefore, not to be taken in a limited sense.

[0041] The functions or algorithms described herein may be implemented in software in an embodiment. The software may comprise computer-executable instructions stored on computer-readable media or computer-readable storage device such as one or more non-transitory memories or other type of hardwarebased storage devices, either local or networked. Further, such functionscorrespond to modules, which may be software, hardware, firmware, or any combination thereof. Multiple functions may be performed in one or more modules as desired, and the embodiments described are merely examples. The software may be executed on a digital signal processor, application-specific integrated circuit (ASIC), a microprocessor, or other type of processor operating on a computer system, such as a personal computer, server, or other computer system, turning such computer system into a specifically programmed machine.

[0042] Computer-readable non-transitory media include all types of computer- readable media, including magnetic storage media, optical storage media, and solid-state storage media and specifically excludes signals. It should be understood that the software can be installed in and sold with the devices that implement arrangements of compute clusters and storage clusters for artificial intelligence training or other data intense operations as taught herein. Alternatively, the software can be obtained and loaded into such devices, including obtaining the software via a disc medium or from any manner of network or distribution system, including, for example, from a server owned by the software creator or from a server not owned but used by the software creator. The software can be stored on a server for distribution over the Internet, for example.

[0043] The following abbreviations apply in this disclosure:ASIC: application-specific integrated circuit BER: bit error rate BWmap: bandwidth map CD: chromatic dispersion CPU: central processing unitDSP: digital signal processing, digital signal processor EAM: electro-absorption modulator EO: electrical-to-opticalFPGA: field-programmable gate array G, Gbit / s: gigabit(s) per second GPON: Gigabit-Capable Passive Optical Networks HSP: high-speed PONIM-DD: intensity modulation - direct modulationITU-T: International Telecommunication Union Telecommunication Standardization Sector km: kilometer(s) krad / s: kiloradian(s) per second ms: millisecond(s) nm: nanometer(s)OE: optical-to-electricalOLT: optical line terminalOMA: optical modulation amplitudeONU: optical network unitPLOAM: physical layer operation, administration, and maintenancePMD: polarization mode dispersionPON: passive optical network ps: picosecond(s)RAM: random-access memoryRF: radio frequencyROM: read-only memoryRSSI: received signal strength indicator RX: receiver, receiver unit SFC. superframe counter SRAM: static RAMTCAM: ternary content-addressable memoryTWDM: time- and wavelength-division multiplexing TX: transmitter, transmitter unit VHSP: very -high-speed PONXG-PON: 10-Gigabit-Capable Passive Optical Networks XGS-PON: 10-Gigabit-Capable Symmetric Passive Optical NetworkZDW: zero-dispersion wavelength.

[0044] There are several methods to mitigate these impairments in optical access systems. The first method of mitigating CD is to pre-distort the transmitted signal, often by introducing a chirp to the optical pulses. This involves deliberately altering the frequency (or wavelength) of the signal acrossthe pulse duration. For instance, if the optical fiber induces dispersion that causes shorter wavelengths to travel more slowly than longer wavelengths, the transmitter can apply a chirp such that the leading edge of the pulse is at a shorter wavelength, while the trailing edge is at a longer wavelength. In this scenario, the back of the pulse (longer wavelengths) travels faster than the front (shorter wavelengths), causing the pulse to compress rather than spread out over the length of the fiber. This is known as negative dispersion compensation, where the dispersion penalty (pulse broadening) is countered.

[0045] Another method is to employ coherent transmission in optical access systems. Coherent receivers recover the full complex electric field of the signal, including both phase and magnitude. This allows DSP at the receiver to compensate for CD and / or PMD impairments.

[0046] The CD is compensated by algorithms that correct the phase delay between different spectral components. PMD is mitigated by dynamically adjusting for the signal's polarization rotation and time delay between different polarization states.

[0047] Both aforementioned methods (the pre-distortion using chirped pulses and the use of coherent transmission) require significant modifications to the optical access system, involving the integration of new devices and hardware. The pre-distortion technique necessitates the use of a chirp modulation device at the transmitter. Coherent transmission demands a more substantial overhaul, including the implementation of both coherent TXs and RXs. These methods imply hardware changes and system redesign, leading to expensive cost and backward incompatibility.

[0048] Many optical access systems operate around the 1310 nm wavelength, primarily because optical fiber specified by ITU-T G.652 has minimal CD in this range. The CD characteristics of these fibers are typically modeled using the Sellmeier equation, where the ZDW and dispersion slope are key parameters.

[0049] In Eq. (1), D, o, and So denote chromatic dispersion coefficient in ps / (nm x km), ZDW in nm, and ZDW slope in ps / (nm2x km), respectively. For most fibers, the ZDW lies between 1300 and 1324 nm, and the slope typically falls between 0.083 and 0.090 ps / nm. However, due to manufacturingvariability, the exact values of ZDW and slope are not predictable, which complicates system design. Transmitter chirp — used to pre-compensate for CD — must be set based on an average CD profile, and designers must account for edge cases to ensure reliable performance across a range of fiber characteristics.

[0050] To reduce channel impairments without coherent operation, many transmission systems aim for multi-channel capacity, and operation in the C band (1530-1565 nm) and L band (1565-1625 nm). As a result, such systems face very high dispersion, which leads to consideration of dispersion compensating fibers or devices. However, these fibers and devices have their own problems: cost, loss, and non-linearity. PON is special because one channel (or maybe two) can be used. At this time, the VHSP system is likely to be reusing the GPON upstream band (1300 to 1320 nm). This coincides with the zero dispersion range of G.652 fiber. The target spectrum for VHSP IM-DD can include the G.652 min-max ZDW range of 1300 to 1324 nm. Statistical link design demonstrates the 99.9% confidence range is 1310 to 1320 nm, which is quite close to the economical tuning range of a transmitter.

[0051] The unpredictability of PMD further exacerbates this challenge. PMD arises from asymmetries in the fiber's geometry' and composition, many of which are introduced during manufacturing, while others result from external stresses, such as cabling, installation in ducts or aerial lines, or physical disturbances. Unlike CD, PMD is highly random and cannot be accurately predicted.

[0052] Based on this analysis, it is clear that both CD and PMD are influenced by a variety of factors, including fiber manufacturing, cabling, installation practices, and operational conditions. Given the complexity and variability of these impairments, a systematic approach to mitigation is essential. This means there is a need to design a mitigation strategy' that operates at the system level. This solution involves monitoring the optical network to detect any impairments as they arise, allowing the system to respond adaptively. Operators can actively manage the impairments and ensure signal quality over the system operation.

[0053] In many cases, controlling the wavelength of the transmitter within a specific range is relatively straightforward. In some optical systems, the primary' goal of wavelength control is to ensure that the signal remains within thedesignated operating band of the system, allowing it to pass through any optical filters along the transmission path. This approach ensures basic compatibility with the network's components and prevents signal loss due to filter misalignment.

[0054] Systems, such as TWDM-PON, have used transmitter tuning to match the signal wavelength to the receiver filter bandwidth, which typically maximizes the RS SI that would lead to a better BER. Channel adaptive tuning adds another objective, which is to tune the transmitter to reduce the impact of channel impairments. Suppose the transmitter has zero chirp. Then, the optimal wavelength will be that of the ZDW of the actual link. If the transmitter is tuned to that wavelength, then the CD penalty will be minimized. Suppose the transmitter has positive chirp. Then, the optimal wavelength will be shorter than the ZDW of the actual link. There is potential to create two or more channels using this concept.

[0055] By considering the link as a control system, several instrumentalities can be used: a measure of the signal error, an algorithm to produce a control signal, a means to send that a control signal to the transmitter, and an effector to change the transmitter. With respect to the measure of error, raw BER can be an ultimate measure. Estimates of the OMA can also be useful. With respect to the algorithm to produce a control signal, the impairments may be assumed to have a parabolic characteristic, and a dithering algorithm can be implemented to seek the minimum of the characteristic. With respect to the means to send a control signal to the transmitter, a protocol to send tuning messages or indications can be used. A time scale can be considered, for example, approximately 10 ms for PLOAM or approximately 0. 125 ms for a BWmap. With respect the effector to change the transmitter, the simplest means can be temperature control, which is almost free, given that the transmitter will be cooled. Bias point control of the EAM can also be used to control the level of chirp.

[0056] CD is quite stable, and will not change much over the life of the link and. therefore, a control system to address CD can be straightforward. PMD, on the other hand, is rapidly changing. The classical rule of thumb is that polarization may rotate up to 50 krad / s. This is a transport number, and so it is based on very long links, for example, approximately 1000 km. Access links are much shorter, for example, approximately 10 km, but the cables are moreexposed to disturbance. However, the characteristic of PMD is that it is an unlikely occurrence. In other words, the birefringence of the fiber needs to “line up” in a correlated fashion along the fiber to have a deleterious effect.Therefore, to avoid PMD-related outage, it may be sufficient to move off the “bad spot” by changing the wavelength. PMD impairment would likely appear as a random noise in the error signal, and it will have the effect to push the transmitter to a different wavelength.

[0057] Controlling the transmitter to minimize channel impairments can be a relevant method to enable 1M-DD for VHSP. The likely wavelengths to be used coincide with the ZDW of the fiber, and so wavelength control can have a significant effect on CD. Implementing such a link control system may be cost effective, because many of the functions are already present in PON. The effectiveness depends on real fiber characteristics that are not easily modelled.

[0058] Wavelength control can be leveraged for more than just ensuring signal passage through filters. By fine-tuning the transmitter's wavelength, optical path impairments such as CD and PMD can be actively minimized, and overall system performance can be improved. This concept is especially relevant when considering the variability of CD and PMD impairments.

[0059] Disclosed herein are embodiments for mitigating channel impairments with wavelength tuning. Transmitter wavelength tuning can mitigate optical channel impairments. The tuning can reuse available PON performance monitoring results as receiver feedback. The receiver feedback helps the transmitter to select the wavelength with satisfactory signal performance. Other than a minor extension to transmit the receiver feedback, there are no requirements on new devices or signal processing redesign. Alternatively, default wavelengths with degraded performance can be used, or the system can be redesigned using a more complicated and expensive design such as coherent transmission or chirped TX.

[0060] To mitigate channel impairments, the operating wavelength is finetuned and controlled at system start-up and during the system operation. Figure 1 represents an embodiment of an example closed-loop transmitter wavelength tuning control mechanism 100. At 1 10, a transmitter performs signal transmission to a receiver via an optical fiber, where the signal transmission is an optical signal having a wavelength. At the optical transmitter, data is receivedfrom the receiver that receives the signal transmission. At 120, data received in feedback from the receiver regarding the optical signal can be evaluated at the transmitter with respect to impairment of the optical signal received by the receiver. At 130, a processor at the transmitter can determine whether signal degradation of the optical signal received by the receiver is larger than a selected threshold. If the signal degradation is larger than the threshold, the wavelength of the optical signal being transmitted by the transmitted can be tuned at 140 and transmitted as a signal transmission such as signal transmission 110. If the signal degradation is not larger than the threshold, the transmitted can continue to transmit as a signal transmission 1 10 without changing the wavelength.Based upon the feedback on the received signal from the receiver, the transmitter continuously adjusts its wavelength to minimize optical impairments, thereby reducing the BER and / or other factors that degrade signal quality. By actively controlling the transmitter's wavelength, the signal integrity is maintained throughout the transmission.

[0061] A key component of this approach is for the receiver to continuously provide feedback to the transmitter regarding the quality of the received signal. This feedback could include metrics such as the current BER, received optical modulation amplitude, or other performance indicators. This feedback can enable the transmitter to make an impairment evaluation and then dynamically adjust its wavelength. The signal could therefore be optimized for the best possible performance.

[0062] It is important to note that the feedback metrics can be derived from the existing optical access system. They can be primarily the performance management data already collected at the receiver. This approach does not require any changes to the hardware or the overall system design, as the necessary data are readily available within the cunent infrastructure.

[0063] From the viewpoint of system control in the context of Figure 1, channel impairments such as CD and PMD behave like a transient noise source within the transmitter wavelength control system. As long as the control system can operate at a timescale faster than the CD and PMD variations, it can dynamically adjust the transmitter's wavelength to mitigate the impact of impairments.

[0064] As analyzed above, the precise values of the ZDW and its dispersion slope can vary due to manufacturing inconsistencies, fiber composition, and / or environmental conditions. This inherent variability makes it challenging to predict the exact CD characteristics of the fiber during system design and deployment. The mechanism illustrated in Figure 1 addresses this uncertainty’ by enabling the transmitter to dynamically scan the operating wavelength range in real time. By continuously adjusting and fine-tuning its wavelength, the transmitter can identify the optimal wavelength that minimizes CD and / or other impairments. This active wavelength scanning allows the system to adapt to the specific dispersion profile of each fiber, compensating for variations in ZDW and slope that may not have been accounted for during manufacturing.

[0065] As previously mentioned, PMD is highly unpredictable and varies over time. It is also wavelength-dependent, with different wavelengths experiencing varying levels of PMD. When a link begins to degrade due to PMD, adjusting the wavelength can help shift the signal away from the affected “bad spot.” Since PMD impacts each wavelength differently, the chances are high that the new wavelength will experience less impairment, restoring the link's functionality. The control system would then maintain the transmitter at the new, optimal wavelength until PMD conditions change again.

[0066] With respect to the operational relationship of a transmitter at one node and a receiver at another node, assume a Node A has a transmitter to communicate with a Node B. The receiver feedback from Node B is crucial to the transmitter wavelength tuning control at Node A. A communication channel is established to relay receiver feedback from node B back to the transmitter at node A. There are two configurations for receiver feedback communication: single-directional, which is unidirectional, or bidirectional.

[0067] Figure 2 illustrates the principles of an embodiment of an example single-sided wavelength tuning control in a communication arrangement 200. At 210, the transmitter at Node A transmits an optical signal at a first wavelength Xi that is received at the receiver at 215. At 220, Node B provides feedback to Node A, which feedback is received at 225. The feedback includes performance data of the optical signal at a first wavelength Xi. The performance data can be related to, but is not limited to, BER. At Node A, the performance data can be evaluated with respect to a threshold level; for example, a determination ofwhether the BER is high or low. At 230, Node A transmits the optical signal tuned to a second wavelength Xi + 5 to the receiver at Node 235. At 240, Node B provides feedback to Node A, which feedback is received at 245. If at Node A. the BER of the optical signal at the second wavelength of Xi + 5 is high, at 250, Node A transmits the optical signal tuned to a third wavelength Xi + to the receiver at Node 255. The value of the wavelength adjustment can depend on the evaluation of the feedback data. At 260, Node B provides feedback to Node A. which feedback is received at 265. If at Node A, the BER of the optical signal at the third wavelength Xi + is evaluated to be low, at 270, Node A keeps the transmitter transmitting at the third wavelength Xi + c, to the receiver at Node 275. The transmission of the optical signal at the third wavelength is maintained until the completion of the transmission event or until it is determined by the feedback process that the optical signal has again exceeded the performance threshold.

[0068] In single-sided operation, only the forward link from Node A to Node B undergoes wavelength control, while the backward link from Node B to Node A functions without dynamic tuning. This approach offers the advantage of starting the backward link first, allowing it to be fully operational when the forward link is initiated. Data and performance statistics gathered from the backward link can then be used to guide the startup of the forw ard link. During startup, the transmitter at Node A can perform a wavelength scan until the signal is successfully detected by Node B. Once Node B identifies that the signal is near the optimal wavelength, it can notify Node A. At that point, the link transitions into normal operating mode, and any necessary incremental adjustments to the wavelength can be made in real time to maintain optimal performance.

[0069] An example of a stable backward link is an OLT equipped with a broadband optical receiver, which can detect and receive a wide range of optical signals from node B. This broad reception capability allows the backward link to function reliably, even as the forward link undergoes wavelength scanning and tuning. The backward link's stability ensures that the forward link can be initialized by leveraging feedback from the already-established communication path. As the transmitter at node A scans for the optimal wavelength, the realtime feedback from node B that is received via the backward link can guide thetuning process to lock onto the best operating wavelength.

[0070] When the backward link is not yet a stable, established path, the situation becomes more complex. In double-sided wavelength tuning control, where both the forward and backward links require wavelength control, the startup process is more challenging because there is no pre-existing feedback channel to guide the initial wavelength adjustments. However, several strategies can be employed to overcome this challenge.

[0071] One method is to temporarily reduce the signaling speed during startup. Slowing down the transmission rate decreases the impact of optical impairments, making communication possible even under suboptimal conditions. Once communication is established, the system can fine-tune the wavelength and then increase the signaling rate to its full capacity once the link is properly adjusted.

[0072] Alternatively, the two sides of the link can perform their initial wavelength scans at different rates. With different wavelength scanning intervals or speeds, the likelihood that the wavelengths in both directions will align is increased. Once this happens, a stable bidirectional communication is established. The link can shift to its operational state with both directions optimally tuned.

[0073] A third approach involves time-stamping feedback messages. During the initial scanning phase, each side of the link could send timestamped feedback. The receiver can identify which timestamped feedback was received with the best qualify, and then repeatedly transmit this specific timestamp value back to the other side. As the receiver continues its own scan, the return link will eventually stabilize. The feedback message containing the best timestamped signal can be received. The transmitter will then know which wavelength setting is optimal.

[0074] Figure 3 illustrates an embodiment of an example time-stamping feedback message arrangement 300. At Node A, a set of optical signals of different wavelengths is transmitted to a receiver at Node B. The set, transmitted at Node A, can include an optical signal at wavelength XI timestamped time tl, an optical signal at wavelength X2 timestamped time t2 . . . an optical signal at wavelength Xn timestamped time tn. At Node B, evaluation is made of the received set 310 of n timestamped optical signals as to which of the received optical signals is best. For example, the optical signal timestamped t6 isdetermined to be the best of the n timestamped optical signals. Node B feedbacks optical signals to Node A in a set 320 of different times at different wavelengths. The set 320 of optical signals feedback from Node B to Node A can include a first optical signal at wavelength W1 timestamped time Tl, an optical signal at wavelength W2 timestamped time with the pair (T2, t6) . . . an optical signal at wavelength Wm timestamped with the pair (TM, t6). The time stamp pair (TK, t6) is the time stamp of transmission from Node B to Node A at TK and the time stamp of the optical signal determined to be the best in the received set 310. At Node A, a determination is made as to the best signal from Node B. If signal with timestamp T2 is determined to be the best, timestamp T2 can be added to the receiver feedback. The set 330 of optical signals at Node A is tuned to transmitted with timestamp pairs of the time of transmission and T2 at wavelength 6. corresponding to time t6 of received set 310. From the received set 340 at Node B that provided feedback regarding timestamp T2, Node B tunes its transmitter to wavelength W2 at corresponds to T2. In PON systems, the timestamp can reuse the existing SFC value. The receiver feedback can be carried using a new PLOAM message, or an extension of existing PLOAM messages, or even in the embedded 0AM fields.

[0075] Figure 4 is a diagram of an example apparatus that can implement channel impairment mitigation via wavelength tuning. The apparatus 400 may implement the disclosed embodiments. The apparatus 400 can include ingress ports 410 and an RX 420 or receiving means to receive data; a processor 430 or processing means, or logic unit, baseband unit, or CPU, to process the data; a TX 440 or transmitting means and egress ports 450 to transmit the data; and a memory 460 or data storing means to store the data. The RX 420 is coupled or connected to the ingress ports 410 and the processor 430, the processor 430 is coupled or connected to the RX 420, the memory 460, and the TX 440, and the TX 440 is coupled to or connected to the processor 430 and the egress ports 450. The apparatus 400 may also comprise OE components, EO components, or RF components coupled to the ingress ports 410, the RX 420, the TX 440, and the egress ports 450 to provide ingress or egress of optical signals, electrical signals, or RF signals. The apparatus 400 can be implemented at a Node A that transmits optical signals to a Node B via an optical fiber for use as in communication arrangement 200 of Figure 2 or as in time-stamping feedback messagearrangement 300 of Figure 3. The apparatus 400 can be implemented at a Node B to receive optical signals from a Node A via an optical fiber for use as in communication arrangement 200 of Figure 2 or as in time-stamping feedback message arrangement 300 of Figure 3.

[0076] The processor 430 is any combination of hardware, middleware, firmware, or software. The processor 430 comprises any combination of one or more CPU chips, cores, FPGAs, ASICs, or DSPs. The processor 430 communicates with the ingress ports 410, the RX 420, the TX 440, the egress ports 450, and the memory 460. The processor 430 comprises a wavelength tuning component 470, which implements the disclosed embodiments including, but not limited to, the operations associated with method 5 below and variations of method 5. The inclusion of the wavelength tuning component 470 therefore provides a substantial improvement to the functionality of the apparatus 400 and effects a transformation of the apparatus 400 to a different state. Alternatively, the memory 460 stores the wavelength tuning component 470 as instructions, and the processor 430 executes those instructions.

[0077] The memory’ 460 comprises any combination of disks, tape drives, or solid-state drives. The apparatus 400 may use the memory 460 as an overflow data storage device to store programs when the apparatus 400 selects those programs for execution and to store instructions and data that the apparatus 400 reads during execution of those programs. The memory 460 may be volatile or non-volatile and may be any combination of ROM, RAM. TCAM, or SRAM, for example. Other memories or memory types are contemplated and fall within the scope of this disclosure.

[0078] A computer program product may comprise computer-executable instructions that are stored on a computer-readable medium and that, when executed by a processor, cause an apparatus to perform any of the embodiments. The non-transitory medium may be the memory 460, the processor may be the processor 430, and the apparatus may be the apparatus 400.

[0079] Figure 5 is a flow diagram of features of an embodiment of an example method 500 of mitigating channel impairments via wavelength tuning. At 510, an optical signal is generated by and from a transmitter to a receiver via an optical fiber. The optical signal is transmitted having a selected wavelength. At 520, adjustment of the wavelength of the optical signal generated by thetransmiter is controlled, using a processor, in response to feedback from the receiver regarding the optical signal received by the receiver.

[0080] Variations of method 500 or methods similar to the method 500 can include a number of different embodiments that may be combined depending on the application of such methods and / or the architecture of devices or systems in which such methods are implemented. Such methods can include continually monitoring for feedback from the receiver and adjusting the wavelength of the optical signal generated by the transmiter based on monitoring the feedback.

[0081] Variations of method 500 or methods similar to the method 500 can include controlling tuning of the wavelength of the optical signal, generated by the transmiter, based on a determination that signal degradation of the optical signal received by the receiver is larger than a threshold level of signal degradation. Variations can include controlling tuning of the wavelength of the optical signal, generated by the transmiter, based on an evaluation of signal impairment from data received in the feedback from the receiver. The generated data can include data associated with bit error rate of the optical signal generated by the transmiter and received by the receiver. Other performance metrics can be used.

[0082] Variations of method 500 or methods similar to the method 500 can include generating a set of multiple optical signals at different wavelengths, where the set includes the optical signal, and identifying one optical signal of the set of multiple optical signals as being beter than the other optical signals of the set, where the identification of the one optical signal is received at the transmitter in the feedback from the receiver. Tuning of the wavelength of the optical signal, generated by the transmiter, can be controlled based on the identification of the one optical signal of the set of multiple optical signals. In an approach, a timestamp can be incorporated in each optical signal of the set generated by the transmiter, where the timestamp is different from timestamps of the other optical signals of the set. At the transmiter, a set of multiple feedback optical signals transmited at different times can be received as the feedback from the receiver. One or more feedback optical signals of the set of multiple feedback optical signals can include a receiver timestamp for the respective feedback optical signal and the timestamp of the one optical signal of the set of multiple optical signals generated by the transmiter identified as beingbetter than the other optical signals transmitted to the receiver.

[0083] Variations of method 500 or methods similar to the method 500 can include the transmitter continually transmitting the optical signal from the transmitter at the wavelength until evaluation of the feedback produces the adjustment.

[0084] Variations of method 500 or methods similar to the method 500 can include evaluating, using a second processor coupled to the receiver at the receiver, the optical signal received by the receiver in communication with the transmitter via the optical fiber. Using the second processor, data can be generated to be fed back to the transmitter, where the data is associated with adjustment of the wavelength of the optical signal generated by the transmitter. A second transmitter coupled to the second processor can transmit the generated data to the transmitter as the feedback from the receiver.

[0085] In various embodiments, a non-transitory machine-readable storage device, such as computer-readable non-transitory medium, can comprise instructions stored thereon, which, when performed by a machine, cause the machine to perform operations, where the operations comprise one or more features similar to or identical to features of methods and techniques described with respect to method 500, variations thereof, and / or features of other methods taught herein such as associated with Figures 1-4. The physical structures of such instructions may be operated on by one or more processors. For example, executing these physical structures can cause the machine to perform operations comprising generating an optical signal by and from a transmitter to a receiver via an optical fiber, where the optical signal has a selected wavelength; and controlling adjustment of the wavelength of the optical signal generated by the transmitter in response to feedback from the receiver regarding the optical signal. The operations can be directed to the evaluation and control of adjustment of the wavelength.

[0086] Variations of the operations can include a number of different embodiments that may be combined depending on the application of such operations and / or the architecture of devices or systems in which such operations are executed. Such operations can include continually monitoring for the feedback from the receiver and adjusting the wavelength of the optical signal generated by the transmitter based on monitoring the feedback. The operationscan include controlling tuning of the wavelength of the optical signal, generated by the transmitter, based on a determination that signal degradation of the optical signal received by the receiver is larger than a threshold level of signal degradation. The operations can include controlling tuning of the wavelength of the optical signal, generated by the transmitter, based on an evaluation of signal impairment from data received in the feedback from the receiver. The generated data can include data associated with bit error rate of the optical signal generated by the transmitter.

[0087] Variations of the operations can include generating a set of multiple optical signals at different wavelengths, where the set includes the optical signal; and identifying one optical signal of the set of multiple optical signals as being better than other optical signals of the set, where identification of the one optical signal is received in the feedback from the receiver. Tuning of the wavelength of the optical signal, generated by the transmitter, can be controlled based on the identification of the one optical signal of the set of multiple optical signals. The operations can further include incorporating, in each optical signal of the set generated by the transmitter, a timestamp different from timestamps of the other optical signals of the set. A set of multiple feedback optical signals transmitted at different times can be received at the transmitter as the feedback from the receiver, where one or more feedback optical signals of the set of multiple feedback optical signals can include a receiver timestamp for the respective feedback optical signal and the timestamp of the one optical signal of the set of multiple optical signals generated by the transmitter and identified as being better than the other optical signals.

[0088] Variations of the operations can include controlling the transmitter to continually transmit the optical signal from the transmitter at the selected wavelength until evaluation of the feedback produces the adjustment.

[0089] Variations of the operations can include evaluating, using a second processor coupled to the receiver at the receiver, the optical signal received by the receiver in communication with the transmitter via the optical fiber. The second processor can execute operations to generate data to be fed back to the transmitter, where the data is associated with adjustment of the wavelength of the optical signal generated by the transmitter. The second transmitter coupled to the second processor can control transmission of the generated data to thetransmiter as the feedback from the receiver.

[0090] The instructions, when executed by the one or more processors, can cause the one or more processors to perform operations to tune the wavelength of the optical signal transmited by the transmitter to mitigate optical channel impairments of the optical fiber.

[0091] The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general-purpose processor, a digital signal processor (DSP), an ASIC, a FPGA (field-programmable gate array) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

[0092] Using transmiter wavelength tuning can mitigate optical channel impairments. Previous PON specifications do not use performance monitoring results as receiver feedback to conduct wavelength fine tuning. Fine tuning transmitter wavelength, as disclosed herein, provides a system solution to mitigate CD and / or PMD, utilizing receiver feedback that provides real-time performance monitoring. In addition, other than minor extension to transmit the receiver feedback, the architecture and methodology does not require new devices. The methodology can reuse existing PON performance monitoring results as receive feedback. The receiver feedback helps the transmiter to select the wavelength that satisfies signal performance.

[0093] Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary' skill in the art that any arrangement that is calculated to achieve the same purpose may be substituted for the specific embodiments shown. Various embodiments use permutations and / or combinations of embodiments described herein. The above description is intended to be illustrative, and not restrictive, and that the phraseology or terminology employed herein is for the purpose of description. Combinations ofthe above embodiments and other embodiments will be apparent to those of skill in the art upon studying the above description.

Claims

CLAIMSWhat is claimed is:

1. A system comprising: a transmitter configured to generate an optical signal to a receiver via an optical fiber, the optical signal having a wavelength; and a processor configured to control adjustment of the wavelength of the optical signal generated by the transmitter in response to feedback from the receiver regarding the optical signal.

2. The system of claim 1, wherein the processor continually monitors the feedback from the receiver and adjusts the wavelength of the optical signal generated by the transmitter based on the feedback.

3. The system of any one of the preceding claims, wherein the processor is structured to control tuning of the wavelength of the optical signal, generated by the transmitter, based on a determination that signal degradation of the optical signal received by the receiver is larger than a signal degradation threshold level of signal degradation.

4. The system of any one of the preceding claims, wherein the processor is structured to control the tuning of the wavelength of the optical signal generated by the transmitter, based on an evaluation of signal impairment from data received in the feedback from the receiver.

5. The system of claim 4, wherein the data includes bit error rate (BER) data associated with a bit error rate of the optical signal generated by the transmitter.

6. The system of any one of the preceding claims, wherein the processor is structured to control tuning of the wavelength of the optical signal generated by the transmitter, based on an identification of one optical signal of a set of multiple optical signals at different wavelengths being better than other optical signals of the set of multiple optical signals, the identification of the one optical signal being received in the feedback from the receiver.

7. The system of claim 6, wherein: each optical signal of the set of multiple optical signals generated by the transmitter includes a timestamp different from timestamps of the other optical signals of the set of multiple optical signals; the feedback from the receiver includes a set of multiple feedback optical signals transmitted at different times; and one or more feedback optical signals of the set of multiple feedback optical signals includes a receiver timestamp for the respective feedback optical signal and the timestamp of the one optical signal of the set of multiple optical signals identified as being better than the other optical signals .

8. The system of any one of the preceding claims, wherein the transmitter continues to transmit the optical signal at the wavelength until evaluation of the feedback produces the adjustment.

9. The system of any one of the preceding claims, wherein the system includes: the receiver in communication with the transmitter via the optical fiber, the receiver configured to receive the optical signal generated by the transmitter; a second processor coupled to the receiver at the receiver to evaluate the received optical signal control and generate feedback data to be fed back to the transmitter, the feedback data being associated with the adjustment of the wavelength of the optical signal generated by the transmitter; and a second transmitter coupled to the second processor to transmit the generated feedback data to the transmitter as the feedback from the receiver.

10. A method comprising: generating an optical signal by and from a transmitter to a receiver via an optical fiber, the optical signal having a wavelength; and controlling, using a processor of the transmitter, adjustment of the wavelength of the optical signal generated by the transmitter in response to feedback from the receiver regarding the optical signal.

11. The method of claim 10, wherein the method includes continually monitoring for the feedback from the receiver and adjusting the wavelength of the optical signal generated by the transmitter based on the feedback.

12. The method of any one of the preceding claims 10 - 11, wherein the method includes controlling tuning of the wavelength of the optical signal, generated by the transmitter, based on a determination that signal degradation of the optical signal received by the receiver is larger than a signal degradation threshold level of signal degradation.

13. The method of any one of the preceding claims 10 - 12, wherein the method includes controlling the tuning of the wavelength of the optical signal generated by the transmitter, based on an evaluation of signal impairment from data received in the feedback from the receiver.

14. The method of claim 13, wherein the method includes generating the data to include bit error rate (BER) data associated with a bit error rate of the optical signal generated by the transmitter.

15. The method of any one of the preceding claims 10 - 14, wherein the method includes: generating a set of multiple optical signals at different wavelengths, the set including the optical signal; identifying one optical signal of the set of multiple optical signals as being better than other optical signals of the set of multiple optical signals, identification of the one optical signal being received in the feedback from the receiver; andcontrolling tuning of the wavelength of the optical signal generated by the transmitter based on the identification of the one optical signal of the set of multiple optical signals.

16. The method of claim 15, wherein the method includes: incorporating in each optical signal of the set of multiple optical signals generated by the transmitter a timestamp different from timestamps of the other optical signals of the set of multiple optical signals; receiving a set of multiple feedback optical signals transmitted at different times as the feedback from the receiver, one or more feedback optical signals of the set of multiple feedback optical signals including a receiver timestamp for the respective feedback optical signal and the timestamp of the one optical signal of the set of multiple optical signals identified as being better than the other optical signals.

17. The method of any one of the preceding claims 10 - 16, wherein the method includes the transmitter continually transmitting the optical signal from the transmitter at the wavelength until evaluation of the feedback produces the adjustment.

18. The method of any one of the preceding claims 10 - 17, wherein the method includes: evaluating, using a second processor coupled to the receiver at the receiver, the optical signal received by the receiver in communication with the transmitter via the optical fiber; generating, using a second processor, feedback data to be fed back to the transmitter, the feedback data being associated with the adjustment of the wavelength of the optical signal generated by the transmitter; and transmitting, using a second transmitter coupled to the second processor, the generated feedback data to the transmitter as the feedback from the receiver.

19. A non-transitory computer-readable storage medium storing instructions, wherein the instructions, when executed by one or more processors, cause the one or more processors to perform operations comprising functions associated with any one of the methods of claims 10 - 18.

20. The non-transitory computer-readable storage medium of claim 19, wherein the instructions, when executed by one or more processors, cause the one or more processors to perform operations to tune the wavelength of the optical signal transmitted by the transmitter to mitigate optical channel impairments of the optical fiber.

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