Joint backscatter suppression and polarization tracking

Abstract

Various example embodiments supporting optical communication in an optical communication system may be configured to support joint stimulated Brillouin scattering (SBS) suppression and polarization tracking for a set of orthogonal polarization light channels in an intensity modulation / direct sounding (IM / DD) passive optical network (PON). Various example embodiments may be configured to support joint SBS suppression and polarization tracking for a set of orthogonal polarization channels based on a set of frequency tones (e.g., using a single frequency tone for each optical channel in the set of orthogonal polarization channels, respectively), such that SBS suppression is supported for transmissions from the transmitter (e.g., based on application of frequency tones to optical channels) and polarization tracking is supported at the receiver (e.g., based on using one or more of the frequency tones of optical channels of the set of orthogonally polarized light channels for polarization tracking).

Description

Technical Field

[0001] Various example embodiments relate generally to optical communication systems and, more particularly, but not exclusively, to supporting communications in a passive optical network (PON). Background Art

[0002] Various communication technologies may be used to support communications in various types of communication networks. Summary of the invention

[0003] In at least some example embodiments, a system includes a transmitter and a receiver. The transmitter is configured to apply a first frequency tone to a first optical channel based on a first polarization and a second frequency tone to a second optical channel based on a second polarization, wherein the first frequency tone and the second frequency tone are configured to support suppression of stimulated Brillouin scattering for transmission from the transmitter, and wherein the first frequency tone and the second frequency tone are different. The receiver is configured to utilize at least one of the first frequency tone or the second frequency tone for polarization tracking of at least one of the first optical channel based on the first polarization or the second optical channel based on the second polarization. In at least some example embodiments, the first frequency tone and the second frequency tone are within a frequency tone range configured to support suppression of stimulated Brillouin scattering. In at least some example embodiments, at least one of the first frequency tone or the second frequency tone is applied to amplitude modulation to support suppression of stimulated Brillouin scattering for transmission from the transmitter. In at least some example embodiments, at least one of the first frequency tone or the second frequency tone is applied to phase modulation to support suppression of stimulated Brillouin scattering for transmission from the transmitter. In at least some example embodiments, the first frequency tone is applied to at least one of: a digital-to-analog converter associated with the first optical channel, an electrical amplifier associated with the first optical channel, a laser associated with the first optical channel, an external modulator associated with the first optical channel, a phase modulator associated with the first optical channel, or an optical amplifier associated with the first optical channel. In at least some example embodiments, in at least some example embodiments, the second frequency tone is applied to at least one of: a digital-to-analog converter associated with the second optical channel, an electrical amplifier associated with the second optical channel, a laser associated with the second optical channel, an external modulator associated with the second optical channel, a phase modulator associated with the second optical channel, or an optical amplifier associated with the second optical channel. In at least some example embodiments, the transmitter includes a first frequency tone generator configured to generate the first frequency tone and apply the first frequency tone to the first optical channel, and a second frequency tone generator configured to generate the second frequency tone and apply the second frequency tone to the second optical channel. In at least some example embodiments, at least one of the first frequency tone or the second frequency tone is extracted from at least one of the first optical channel or the second optical channel.In at least some example embodiments, at least one of the first frequency tone or the second frequency tone is extracted from at least one of an optical-to-electrical converter or an analog-to-digital converter. In at least some example embodiments, the receiver is configured to utilize at least one of the first frequency tone or the second frequency tone for polarization tracking of at least one of the first optical channel or the second optical channel at the receiver. In at least some example embodiments, the receiver is configured to generate a feedback signal for a polarization controller based on at least one of the first frequency tone or the second frequency tone, and to perform polarization tracking of at least one of the first optical channel or the second optical channel at the receiver based on the feedback signal for the polarization controller. In at least some example embodiments, the receiver includes a polarization controller configured to perform polarization tracking for at least one of the first optical channel or the second optical channel; and a controller configured to generate a feedback signal based on at least one of the first frequency tone or the second frequency tone and provide the feedback signal to the polarization controller.

[0004] In at least some example embodiments, an apparatus includes a transmitter. The transmitter is configured to apply a first frequency tone to a first optical channel based on a first polarization and to apply a second frequency tone to a second optical channel based on a second polarization, wherein the first frequency tone and the second frequency tone are configured to support suppression of stimulated Brillouin scattering for transmission from the transmitter, and wherein the first frequency tone and the second frequency tone are different. The transmitter is configured to propagate the first optical channel and the second optical channel toward a receiver, wherein at least one of the first frequency tone or the second frequency tone is configured to be used by the receiver for polarization tracking of at least one of the first optical channel or the second optical channel at the receiver. In at least some example embodiments, a non-transitory computer-readable medium stores computer program instructions that, when executed by an apparatus, cause the apparatus to at least: apply a first frequency tone to a first optical channel based on a first polarization and apply a second frequency tone to a second optical channel based on a second polarization, wherein the first frequency tone and the second frequency tone are configured to support suppression of stimulated Brillouin scattering for transmissions from the transmitter, and wherein the first frequency tone and the second frequency tone are different; and propagate the first optical channel and the second optical channel toward a receiver, wherein at least one of the first frequency tone or the second frequency tone is configured to be used by the receiver for polarization tracking of at least one of the first optical channel or the second optical channel at the receiver. In at least some example embodiments, a method includes: applying a first frequency tone to a first optical channel based on a first polarization and applying a second frequency tone to a second optical channel based on a second polarization, wherein the first frequency tone and the second frequency tone are configured to support suppression of stimulated Brillouin scattering for transmission from the transmitter, and wherein the first frequency tone and the second frequency tone are different; and propagating the first optical channel and the second optical channel toward a receiver, wherein at least one of the first frequency tone or the second frequency tone is configured to be used by the receiver for polarization tracking of at least one of the first optical channel or the second optical channel at the receiver.In at least some example embodiments, an apparatus includes: means for applying a first frequency tone to a first optical channel based on a first polarization and a second frequency tone to a second optical channel based on a second polarization, wherein the first frequency tone and the second frequency tone are configured to support suppression of stimulated Brillouin scattering for transmissions from the transmitter, and wherein the first frequency tone and the second frequency tone are different; and means for propagating the first optical channel and the second optical channel toward a receiver, wherein at least one of the first frequency tone or the second frequency tone is configured to be used by the receiver for polarization tracking of at least one of the first optical channel or the second optical channel at the receiver. In at least some example embodiments, the first frequency tone and the second frequency tone are within a range of frequency tones configured to support suppression of stimulated Brillouin scattering. In at least some example embodiments, at least one of the first frequency tone or the second frequency tone is applied to amplitude modulation to support suppression of stimulated Brillouin scattering for transmissions from the transmitter. In at least some example embodiments, at least one of the first frequency tone or the second frequency tone is applied for phase modulation to support suppression of stimulated Brillouin scattering for transmissions from the transmitter.

[0005] In at least some example embodiments, an apparatus includes a receiver. The receiver is configured to receive a first optical channel based on a first polarization and a second optical channel based on a second polarization from a transmitter. The receiver is configured to extract at least one of a first frequency tone or a second frequency tone from at least one of the first optical channel or the second optical channel, wherein the first frequency tone and the second frequency tone are configured to support suppression of stimulated Brillouin scattering for transmission from the transmitter, and wherein the first frequency tone and the second frequency tone are different. The receiver is configured to perform polarization tracking of at least one of the first optical channel or the second optical channel based on at least one of the first frequency tone or the second frequency tone. In at least some example embodiments, a non-transitory computer-readable medium stores computer program instructions that, when executed by an apparatus, cause the apparatus to at least: receive a first optical channel based on a first polarization and a second optical channel based on a second polarization from a transmitter; extract at least one of a first frequency tone or a second frequency tone from at least one of the first optical channel or the second optical channel, wherein the first frequency tone and the second frequency tone are configured to support suppression of stimulated Brillouin scattering for transmission from the transmitter, and wherein the first frequency tone and the second frequency tone are different; and perform polarization tracking of at least one of the first optical channel or the second optical channel based on at least one of the first frequency tone or the second frequency tone. In at least some example embodiments, a method includes: receiving a first optical channel based on a first polarization and a second optical channel based on a second polarization from a transmitter; extracting at least one of a first frequency tone or a second frequency tone from at least one of the first optical channel or the second optical channel, wherein the first frequency tone and the second frequency tone are configured to support suppression of stimulated Brillouin scattering for transmission from the transmitter, and wherein the first frequency tone and the second frequency tone are different; and performing polarization tracking of at least one of the first optical channel or the second optical channel based on at least one of the first frequency tone or the second frequency tone.In at least some example embodiments, an apparatus includes: means for receiving a first optical channel based on a first polarization and a second optical channel based on a second polarization from a transmitter; means for extracting at least one of a first frequency tone or a second frequency tone from at least one of the first optical channel or the second optical channel, wherein the first frequency tone and the second frequency tone are configured to support suppression of stimulated Brillouin scattering for transmission from the transmitter, and wherein the first frequency tone and the second frequency tone are different; and means for performing polarization tracking of at least one of the first optical channel or the second optical channel based on at least one of the first frequency tone or the second frequency tone. In at least some example embodiments, the first frequency tone and the second frequency tone are within a frequency tone range configured to support suppression of stimulated Brillouin scattering. In at least some example embodiments, the receiver is configured to utilize at least one of the first frequency tone or the second frequency tone for polarization tracking of at least one of the first optical channel or the second optical channel at the receiver. In at least some example embodiments, the receiver is configured to generate a feedback signal for a polarization controller based on at least one of the first frequency tone or the second frequency tone, and to perform polarization tracking of at least one of the first optical channel or the second optical channel at the receiver based on the feedback signal for the polarization controller. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The teachings herein may be readily understood by considering the following detailed description taken in conjunction with the accompanying drawings, in which:

[0007] Figure 1A and Figure 1B An example embodiment of a passive optical network (PON) including an optical line terminal (OLT) and an optical network unit (ONU) is shown, wherein the PON is configured to support joint backscatter mitigation and polarization tracking;

[0008] Figure 2A and Figure 2B An example embodiment of a PON configured to support joint backscatter mitigation at a transmitter and polarization tracking at a receiver is shown;

[0009] Figure 3 An example embodiment of a method for use by a transmitter to support backscatter mitigation in a PON configured to support joint backscatter mitigation and polarization tracking is shown;

[0010] Figure 4An example embodiment of a method for use by a receiver to support polarization tracking in a PON configured to support joint backscatter mitigation and polarization tracking is shown;

[0011] Figure 5 An example embodiment of a computer suitable for performing the various functions presented herein is shown.

[0012] To facilitate understanding, identical reference numerals have been used herein, where possible, to designate identical elements that are common to the various figures. DETAILED DESCRIPTION

[0013] Various example embodiments for supporting optical communications in an optical communication system are presented herein. Various example embodiments for supporting optical communications in an optical communication system may be configured to support joint stimulated Brillouin scattering (SBS) suppression and polarization tracking for a set of orthogonal polarized optical channels in an intensity modulation / direct detection (IM / DD) passive optical network (PON). Various example embodiments for supporting joint SBS suppression and polarization tracking in an IM / DD PON may be configured to support joint SBS suppression and polarization tracking for a set of orthogonal polarized optical channels based on a set of frequency tones (e.g., each optical channel in the set of orthogonal polarized optical channels uses a single frequency tone, respectively), so that SBS suppression is supported for transmission from a transmitter (e.g., based on the application of frequency tones to optical channels in the set of orthogonal polarized optical channels, respectively) and polarization tracking is supported at a receiver (e.g., based on one or more frequency tones in the frequency tones of optical channels in the set of orthogonal polarized optical channels being used for polarization tracking of optical channels in the set of orthogonal polarized optical channels). It should be understood that these and various other example embodiments may be further understood by considering various aspects of a PON system more generally.

[0014] PON systems continue to evolve to support higher rates based on the use of new PON technologies. The ITU-T G.sup.VHSP document, prepared by the International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) Question 2 / Study Group 15 (Q2 / SG15), is a document that will describe requirements and technologies applicable to the implementation of PON solutions above 50G. The scope of technology covered by this document includes, in particular, the use of IM / DD and coherent technologies to provide Very High Speed ​​PON (VHSP) services. Although coherent technology has various benefits, IM / DD technology generally provides lower complexity, power consumption and cost. In addition, the technology of multiplexing a pair of orthogonal polarization channels to IM / DD (orthogonal polarization technology) is applied to provide orthogonal polarization IM / DD transmission for PON, which can enable even higher PON rates (e.g., 200G PON based on IM / DD 100G orthogonal polarization channels, 400G PON based on IM / DE 200G orthogonal polarization channels, or 400G PON based on dual-wavelength IM / DD 100G orthogonal polarization channels, etc.). Although the use of orthogonal polarization techniques can increase PON rates, the use of the orthogonal polarization method requires the application of polarization tracking at the receiver, thereby requiring additional complexity at the receiver of the PON system.

[0015] PON systems designed to achieve higher rates typically rely on using high transmit powers at the transmitter to achieve the required PON link budget and overcome the decreasing receiver sensitivity as the bit rate increases. The high power launched from the transmitter into the fiber creates an effect called stimulated Brillouin scattering (SBS). At very high transmit powers (typically in excess of +10dBm), SBS causes a significant amount of power to be reflected back toward the transmitter. The magnitude of this effect depends on the fiber material properties, fiber length, and transmit power. The amount of reflected power increases as the transmit power increases until any further increase in transmit power does not increase the output power. This can cause problems in PONs because it prevents the link budget from being increased by increasing transmit power. This issue first became relevant in 50G PONs and will continue to be a problem for PONs that use high transmit powers, such as VHSP PONs that rely on IM / DD, with SBS mitigation being considered a potential solution to achieving the required loss budget when launching high powers into the fiber. While the use of SBS suppression can increase the PON link budget, applying SBS suppression techniques at the transmitter requires additional complexity at the receiver of the PON system.

[0016] Various example embodiments presented herein may be configured to support joint SBS suppression and polarization tracking in various PON systems. Example embodiments may be applicable to various PON systems operating at high transmit powers, including existing and potential future PON systems, particularly but not exclusively systems with residual or non-suppressed carriers (such as intensity modulated systems) that employ orthogonal polarization receivers that perform polarization demultiplexing in the optical domain or polarization-sensitive receivers that rely on polarization stabilization / tracking in front of the receiver (e.g., receivers that include polarization-sensitive components or receivers that are based on receiving signals with a reference laser beat), and support polarization tracking based on a low-frequency marker tone. Example embodiments may perform SBS suppression (for all polarization / wavelength channels) and polarization tracking for that channel or an orthogonal polarization channel on a per-transmission channel (polarization or wavelength) basis using a single tone, possibly for multiple wavelength channels at a time.

[0017] Various example embodiments for supporting joint SBS suppression and polarization tracking in a PON system can be based on SBS suppression performed based on phase modulation. In at least some example embodiments, SBS suppression can be achieved by phase broadening of the source laser linewidth, which can be achieved in various ways as further discussed below. For example, SBS suppression can be performed using electrical or mechanical modulation, carrier suppression or carrier reduction modulation formats, SBS dithering (e.g., where dithering can be applied optically or electrically), etc. and various combinations thereof. Polarization tracking / alignment is then performed at the receiver using the same tone used to induce phase modulation to provide SBS suppression. It should be understood that in the context of supporting joint SBS suppression and polarization tracking, the per-channel tone can be used in various other ways to support SBS suppression based on phase modulation.

[0018] Various example embodiments for supporting joint SBS suppression and polarization tracking in a PON system can be based on SBS suppression performed based on amplitude modulation. In at least some example embodiments, SBS suppression can be performed by amplitude modulation of a semiconductor laser, which causes phase modulation of the signal due to amplitude-phase coupling in the semiconductor device (e.g., injection of an electrical carrier during amplitude modulation changes the cavity refractive index, resulting in phase modulation). To this end, devices such as distributed feedback lasers (DFBs), directly modulated lasers (DMLs), electro-absorption modulators (EAMs), external modulators (e.g., Mach-Zehnder modulators, etc.), or various combinations thereof (e.g., electro-absorption modulated lasers (EMLs) or externally modulated lasers) can be used, where the tone can be applied to one of the following: DFB or DML laser bias current, EAM or EML bias voltage, or data signal applied to the DML, EAM, or EML. The same modulation can then be used to perform polarization tracking / alignment by maximizing the amplitude of the tracking tone in the signal after the polarization splitter / polarizer (generally any optical element with a high polarization extinction ratio). It should be understood that in the context of supporting joint SBS suppression and polarization tracking, the per-channel tone can be used in various other ways to support amplitude modulation-based SBS suppression.

[0019] Various example embodiments for supporting joint SBS suppression and polarization tracking in a PON system can be based on polarization tracking, which, as described above, can be provided in various ways (at least some of which may depend on the manner in which SBS suppression is implemented). Since each polarized channel uses a different tone for SBS suppression, tracking / alignment can also be performed by minimizing the tones of the orthogonal polarized channels or based on a joint metric based on two or more tones originating from two or more channels. The amplitude and frequency of one or more tones applied to SBS suppression and polarization tracking on each channel can be adjusted to provide an optimal compromise between SBS suppression efficiency and polarization tracking / alignment error. For example, since multiple SBS jitter tones can provide better SBS suppression efficiency than a single tone, each polarized channel in an orthogonal polarization system can use amplitude tones of different frequencies to provide high SBS suppression efficiency, combined with the benefit of allowing polarization tracking / alignment to be performed at the receiver using a dual-tone metric. It should be understood that in the context of supporting joint SBS suppression and polarization tracking, the per-channel tone can be used in various other ways to support polarization tracking.

[0020] It should be understood that these and various other example embodiments for supporting joint SBS suppression and polarization tracking in a PON system, as well as the advantages or potential advantages of supporting joint SBS suppression and polarization tracking in a PON system, can be further understood by reference to the various accompanying drawings, which will be further discussed below.

[0021] Figure 1A and Figure 1B An example embodiment of a passive optical network (PON) including an optical line terminal (OLT) and an optical network unit (ONU) is shown, wherein the PON is configured to support joint backscatter mitigation and polarization tracking.

[0022] The PON 100 is configured to provide broadband network access to end customers using fiber optic telecommunication technology to support communications for these end customers. The PON 100 includes an optical line terminal (OLT) 110 and a group of optical network units (ONUs) 120-1 to 120-N (collectively referred to as ONUs 120) connected via an optical distribution network (ODN) 130. The PON 100 can be configured to support downstream communications from the OLT 110 to the ONUs 120 via the ODN 130 and upstream communications from the ONUs 120 to the OLT 110 via the ODN 130. The PON 100 can be configured to operate using various types of PON technologies that can be based on various PON standards to implement various types of PONs (e.g., 50G PON, 100G PON, 200G PON, 400G PON, etc., and various combinations thereof). It should be understood that the PON 100 may include various other elements that have been omitted for clarity purposes, may be based on various other PON technologies and / or standards, etc., as well as various combinations thereof.

[0023] The OLT 110 is configured to support communication between the ONU 120 and one or more upstream networks (omitted for clarity). The OLT 110 may be located at a central location relative to the ONU 120, such as a central office (CO) or other suitable location located near the ONU 120. For example, the one or more upstream networks may include one or more core communication networks configured to support communication between the OLT 110 and the ONU 120. For example, the OLT 110 may be configured to forward data received from the one or more upstream networks downstream toward the ONU 120 through the ODN 130, and forward data received from the ONU 120 upstream toward the one or more upstream networks through the ODN 130. The OLT 110 includes a transmitter 111 that is configured to support orthogonal polarization-based communication from the OLT 110 to the ONU 120 and is configured to support SBS suppression of orthogonal polarization-based communication from the OLT 110 to the ONU 120. It should be appreciated that OLT 110 may include various other components for supporting communications with ONU 120 (eg, one or more receivers for upstream communications from ONU 120 or other suitable components).

[0024] Each of the ONUs 120 is configured to support communication between the OLT 110 and one or more downstream networks or devices (omitted for clarity). The ONUs 120 may be located at a corresponding customer site or other suitable location. For example, the downstream networks or devices of the ONUs 120 may include one or more local area networks (LANs) of the customer, one or more communication devices of the customer (e.g., modems, routers, switches, set-top boxes, smart TVs, gaming systems, computers, smart phones, etc., and various combinations thereof). For example, each of the ONUs 120 may be configured to forward data received from the OLT 110 downstream toward one or more downstream networks or devices through the ODN 130, and forward data received from one or more downstream networks or devices upstream toward the OLT 110 through the ODN 130. ONUs 120-1 to 120-N respectively include receivers 121-1 to 121-N (collectively, receivers 121) configured to support orthogonal polarization-based communications from OLT 110 to ONUs 120 and configured to support polarization tracking of orthogonal polarization-based communications from OLT 110 to ONUs 120. It should be understood that each of ONUs 120 may include various other elements for supporting communications with OLT 110 (e.g., a transmitter or other suitable element for upstream communications to OLT 110).

[0025] The ODN 130 may be a data distribution system configured to support communication between the OLT 110 and the ONU 120. The ODN 130 is configured to support downstream propagation of optical signals from the OLT 110 toward the ONU 120 and upstream propagation of optical signals from the ONU 120 toward the OLT 110. The ODN 130 includes a single-mode optical fiber 131 and an optical splitter 132, wherein the single-mode optical fiber 131 connects the OLT 110 to the optical splitter 132, and wherein the optical splitter 132 supports splitting of downstream optical signals received from the OLT 110 toward the ONU 120 through the single-mode optical fiber 131. It should be understood that although mainly presented as including a single optical splitter 132, the ODN 130 may include a plurality of optical splitters, and the plurality of optical splitters may be hierarchically arranged for splitting the downstream optical signals for transmission to the ONU 120. It should be appreciated that the ODN 130 may include various other elements for supporting communications between the OLT 110 and the ONUs 120 .

[0026] The PON 100 may be configured to support joint SBS suppression and polarization tracking of an orthogonal polarized optical channel pair based on a frequency tone pair (i.e., each optical channel in the orthogonal polarized optical channel pair uses a single frequency tone), such that SBS suppression of transmissions from the transmitter 111 and polarization tracking at the receiver 121 may be achieved based on the frequency tone pair. The frequency tone pair includes a first frequency tone for providing SBS suppression of transmissions from the transmitter 111 for a first optical channel based on a first polarization, and a second frequency tone for providing SBS suppression of transmissions from the transmitter 111 for a second optical channel based on a second polarization, wherein one or both of the first frequency tone and the second frequency tone may be extracted at the receiver 121 and used for polarization tracking of the first optical channel based on the first polarization and polarization tracking of the second optical channel based on the second polarization. The frequency tone pair may be adapted to provide SBS suppression of transmissions from the transmitter 111 (e.g., selected from a range of frequency tones adapted to provide SBS suppression), and may also be adapted to perform polarization tracking at the receiver 121 (e.g., the frequency tones may be different from each other). The use of frequency tone pairs to support joint SBS suppression and polarization tracking in PON 100 is discussed further below.

[0027] The transmitter 111 may be based on intensity modulation (IM) and may support a pair of orthogonal polarization optical channels based on polarization pairs (i.e., a first optical channel based on a first polarization and a second optical channel based on a second polarization). The first optical channel may be based on modulation of data to a first polarization for transmission toward the ONU 120 (e.g., an optical channel carrying data at a first polarization, wherein the optical channel may be formed by modulation of an optical carrier having a data signal carrying data to be transmitted by the optical channel). The second optical channel may be based on modulation of data to a second polarization for transmission toward the ONU 120 (e.g., an optical channel carrying data at a second polarization, wherein the optical channel may be formed by modulation of an optical carrier having a data signal carrying data to be transmitted by the optical channel). In the PON 100, SBS suppression of transmissions from the transmitter 111 may be based on applying a first frequency tone to the first optical channel based on the first polarization, and based on applying a second frequency tone to the second optical channel based on the second polarization.

[0028] The transmitter 111 includes a first IM transmitter 112--1 based on a first polarization and a second IM transmitter 112--2 based on a second polarization, which may be collectively referred to as an IM transmitter. The first IM transmitter 112--1 is configured to generate a first optical channel based on the first polarization for transmitting data from the OLT 110 toward the ONU 120. The second IM transmitter 112--2 is configured to generate a second optical channel based on the second polarization for transmitting data from the OLT 110 toward the ONU 120. The transmitter 111 includes a polarization beam combiner (PBC) 119, which is configured to combine the first optical channel based on the first polarization and the second optical channel based on the second polarization to provide a combined optical signal for transmission toward the ONU 120 via the single-mode optical fiber 131 of the ODN 130.

[0029] The transmitter 111 is configured to support SBS suppression for optical signals transmitted into the single mode optical fiber 131 (e.g., for a combined optical signal based on a first optical channel based on a first polarization and a second optical channel based on a second polarization). The transmitter 111 is configured to support SBS suppression based on applying a pair of frequency tones 115--1 and 115--2 (collectively referred to as frequency tones 115) to the optical channels at the IM transmitter 112. The first frequency tone 115--1 is generated by a frequency tone generator 116--1 and provided to the first IM transmitter 112--1 for applying the first frequency tone 115--1 to the first optical channel based on the first polarization by the first IM transmitter 112--1, and similarly, the second frequency tone 115--2 is generated by a frequency tone generator 116--2 and provided to the second IM transmitter 112--2 for applying the second frequency tone 115--2 to the second optical channel based on the second polarization by the second IM transmitter 112--2. The frequency tone 115 may be applied to the optical channel in various ways for supporting SBS suppression. For example, the frequency tone 115 may be applied to the optical channel by applying the frequency tone 115 to phase modulation (e.g., using the frequency tone 115 for one or more of the following: mechanical or electrical modulation, carrier suppression or carrier reduction modulation formats, electrical or optical SBS dithering, external cavity lasers, etc.) or amplitude modulation (based on applying the frequency tone 115 to one or more of the following: DFB or DML laser bias current, EAM or EML bias voltage, data signal applied to the DML, EAM or EML, etc.).

[0030] Receiver 121 may be direction detection (DD) based and may support orthogonal polarization optical channel pairs based on polarization pairs (i.e., a first optical channel based on a first polarization and a second optical channel based on a second polarization). The first optical channel may support transmission of data using a first polarization based on modulation of the data to the first polarization by OLT 110, and the second optical channel may support transmission of data using a second polarization based on modulation of the data to the second polarization by OLT 110. Receiver 121 may support recovery of data from either or both of the optical channels in the orthogonal polarization optical channel pair (e.g., ONU 120--1 includes receiver 121 that supports recovery of data from both of the optical channels in the orthogonal polarization optical channel pair, while ONU 120--2 includes receiver 121--2 that supports recovery of data from only one of the optical channels in the orthogonal polarization optical channel pair). In PON 100, polarization tracking at receiver 121 can be based on the use of one or both of a first frequency tone (i.e., first frequency tone 115--1) applied to a first optical channel for SBS suppression at OLT 110 or a second frequency tone (i.e., second frequency tone 115--2) applied to a second optical channel for SBS suppression at OLT 110.

[0031] The receiver 121--1 includes a polarization controller 122--1, a polarization beam splitter (PBS) 123--1, a pair of DD receivers 124--1--1 and 124--1--2 (collectively referred to as DD receiver 124--1), and a polarization tracking controller 125--1. The polarization controller 122--1 receives a downstream optical signal from the optical splitter 132 of the ODN 130, performs polarization control to align polarizations of orthogonal polarization optical channels of the downstream optical signal, and provides the polarization-aligned downstream optical signal to the PBS 123--1. The PBS 123--1 receives the polarization-aligned downstream optical signal, splits the polarization-aligned downstream optical signal into a first optical channel based on a first polarization and a second optical channel based on a second polarization, and provides the first optical channel based on the first polarization to the DD receiver 124--1--1, and provides the second optical channel based on the second polarization to the DD receiver 124--1--2. DD receiver 124--1--1 recovers data transmitted by OLT 110 from a first optical channel based on a first polarization, and similarly, DD receiver 124--1--2 recovers data transmitted by OLT 110 from a second optical channel based on a second polarization.

[0032] Receiver 121--1 is configured to support polarization tracking for a pair of orthogonal polarized optical channels (e.g., for a downstream optical signal including a first optical channel based on a first polarization and a second optical channel based on a second polarization). Receiver 121--1 is configured to support polarization tracking for a pair of orthogonal polarized optical channels based on any one or both of the frequency tones 115 used at transmitter 111 for SBS suppression. Frequency tone 115--1 may be extracted from the first optical channel by DD receiver 124--1--1 and provided to polarization tracking controller 125--1. Frequency tone 115--2 may be extracted from the second optical channel by DD receiver 124--1--2 and provided to polarization tracking controller 125--1. Both frequency tones 115--1 and 115--2 may be extracted from one of the optical channels (e.g., from the first optical channel by DD receiver 124--1--1 or from the second optical channel by DD receiver 124--1--2). The polarization tracking controller 125--1 may process the (multiple) frequency tones 115 received from the (multiple) DD receivers 124--1 and generate a feedback signal, which is provided to the polarization controller 122--1 for controlling the polarization alignment of the orthogonal polarization optical channels of the downstream optical signals received at the receiver 121--1. The polarization tracking controller 125--2 may calculate a metric based on the (multiple) frequency tones 115 received from the (multiple) DD receivers 124--1 and generate the feedback signal based on the metric, which is provided to the polarization controller 122--1 for controlling the polarization alignment of the orthogonal polarization optical channels of the downstream optical signals received at the receiver 121--1. The polarization tracking controller 125--2 may calculate the metric with the goal of optimizing one or more settings of the polarization controller 122--1 (e.g., one or more settings configured to maximize one of the frequency tones 115 and minimize another of the frequency tones 115). Frequency tones 115 may be processed by polarization tracking controller 125-1 in various ways to support polarization tracking.

[0033] The receiver 121--2 includes a polarization controller 122--2, a polarizer 123--2, a DD receiver 124--2, and a polarization tracking controller 125--2. The polarization controller 122--2 receives a downstream optical signal from the optical splitter 132 of the ODN 130, performs polarization control for aligning polarizations of orthogonal polarization optical channels of the downstream optical signal, and provides the polarization-aligned downstream optical signal to the polarizer 123--2. The polarizer 123--1 receives the polarization-aligned downstream optical signal, passes a first optical channel based on a first polarization and blocks a second optical channel based on a second polarization (because the DD receiver 124--2 is configured to process an optical signal based on the first polarization), and provides the first optical channel based on the first polarization to the DD receiver 124--2. The DD receiver 124--2 recovers data sent by the OLT 110 from the first optical channel based on the first polarization.

[0034] The receiver 121--2 is configured to support polarization tracking for a pair of orthogonal polarization optical channels (e.g., for a downstream optical signal including a first optical channel based on a first polarization and a second optical channel based on a second polarization). The receiver 121--2 is configured to support polarization tracking for a pair of orthogonal polarization optical channels based on either or both of the frequency tones 115 used for SBS suppression at the transmitter 111. The frequency tones 115 may be extracted from the first optical channel by the DD receiver 124--2 and provided to the polarization tracking controller 125--2. The polarization tracking controller 125--2 may process the frequency tones 115 received from the DD receiver 124--2 and generate a feedback signal, which is provided to the polarization controller 122--2 for controlling the polarization alignment of the orthogonal polarization optical channels of the downstream optical signal received at the receiver 121--2. The polarization tracking controller 125--2 can calculate a metric based on the (multiple) frequency tones 115 received from the DD receiver 124--2, and generate the feedback signal based on the metric, which is provided to the polarization controller 122--2 for controlling the polarization alignment of the orthogonal polarization optical channels of the downstream optical signal received at the receiver 121--2. The polarization tracking controller 125--2 can calculate the metric with the goal of optimizing one or more settings of the polarization controller 122--2 (e.g., one or more settings configured to maximize one of the frequency tones 115 and minimize another of the frequency tones 115). The (multiple) frequency tones 115 can be processed by the polarization tracking controller 125--2 in various ways to support polarization tracking.

[0035] Receiver 121 may be configured to perform polarization tracking in a variety of ways that may depend on the manner in which frequency tone 115 is applied for SBS suppression for transmissions from transmitter 111. For example, when phase modulation based on frequency tone 115 is used at receiver 111 for SBS suppression, then the same frequency tone 115 used for phase modulation to provide SBS suppression for transmissions from receiver 111 may be used at receiver 121 to perform polarization tracking / alignment. For example, where amplitude modulation based on frequency tone 115 is used at transmitter 111 for SBS suppression, then the same modulation may be used to perform polarization tracking / alignment by maximizing the amplitude of frequency tone 115 in the signal after PBS 123--1 / polarizer 123--2 (typically any optical unit with a high polarization cancellation ratio). It should be appreciated that frequency tone(s) 115 may be used in a variety of other ways for supporting polarization tracking at receiver 121.

[0036] It should be appreciated that, although primarily described with respect to particular types, numbers, and arrangements of elements, PON 100 may be implemented using various other types of elements, various other numbers of elements, various other arrangements of elements, etc., as well as various combinations thereof.

[0037] Figure 2A and Figure 2B An example embodiment of a PON configured to support joint backscatter mitigation at a transmitter and polarization tracking at a receiver is shown.

[0038] The PON 200 includes an OLT 210 and an ONU 220 interconnected by a single-mode optical fiber 231. The PON 200 may correspond to Figure 1A and Figure 1B The PON includes an OLT 210 and an ONU pair 220-1 and 220-2 (collectively referred to as ONU 220), wherein the OLT 210 may correspond to Figure 1A and Figure 1B An example embodiment of the OLT 110, and wherein the ONUs 220--1 and 220--2 may correspond to Figure 1A and Figure 1B The PON 200 further includes an ODN 230, wherein the ODN 230 may correspond to Figure 1A and Figure 1B Example embodiments of ODN 130 (eg, including ODNs that may correspond to Figure 1A and Figure 1B 131 and the optical splitter 132 of the exemplary embodiment of the single-mode optical fiber 231 and the optical splitter 232).

[0039] The OLT 210 includes a transmitter 211. The transmitter 211 includes a first IM transmitter 212--1 based on a first polarization and a second IM transmitter 212--2 based on a second polarization, which may be collectively referred to as an IM transmitter 212. The first IM transmitter 212--1 is configured to generate a first optical channel based on a first polarization for transmitting data from the OLT 210 toward the ONU 220. The second IM transmitter 212--2 is configured to generate a second optical channel based on a second polarization for transmitting data from the OLT 210 toward the ONU 220. The transmitter 211 includes a polarization beam combiner (PBC) 219 configured to combine the first optical channel based on the first polarization and the second optical channel 212--2 based on the second polarization, wherein the first polarization and the second polarization are orthogonal to each other, to provide a combined optical signal for transmission toward the ONU 220 via a single mode optical fiber 231 of the ODN 230. Transmitter 211 is configured to support SBS suppression of optical signals transmitted into single mode optical fiber 231 based on application of frequency tone pair 218--1 and 218--2 (collectively, frequency tones 218) to the optical channel at IM transmitter 212.

[0040] The transmitter 211 is configured to support SBS suppression based on the frequency tone 218-1 for the optical signal provided by the first IM transmitter 212-1. The first IM transmitter 212-1 includes a digital-to-analog converter (DAC) 213-1, an electrical amplifier 214-1, a laser 215-1, an electro-absorption modulator (EAM) 216-1, and an optical amplifier 217-1. Figure 2A and Figure 2B As shown, the application of the frequency tone 218-1 to the optical channel associated with the first IM transmitter 212-1 can be based on the application of the frequency tone 218-1 to the DAC 213-1, the application of the frequency tone 218-1 to the laser 215-1 (e.g., via the application of a bias current), or the application of the frequency tone 218-1 to the EAM 216-1 (e.g., via the application of a bias voltage). It should be understood that although primarily presented with respect to a particular embodiment of the first IM transmitter 212-1 (i.e., including particular components arranged in a particular arrangement), the first IM transmitter 212-1 can be implemented in a variety of other ways (e.g., using a different sequence of components, using a different group of components, etc., as well as various combinations thereof), and therefore, the application of the frequency tone 218-1 to the optical channel at the first IM transmitter 212-1 can also be implemented in a variety of other ways.

[0041] The transmitter 211 is configured to support SBS suppression based on the frequency tone 218-2 for the optical signal provided by the second IM transmitter 212-2. The second IM transmitter 212-2 includes a digital-to-analog converter (DAC) 213-2, an electrical amplifier 214-2, a laser 215-2, an electro-absorption modulator (EAM) 216-2, and an optical amplifier 217-2. Figure 2A and Figure 2B As shown, the application of the frequency tone 218-2 to the optical channel associated with the second IM transmitter 212-2 can be based on the application of the frequency tone 218-2 to the DAC 213-2, the application of the frequency tone 218-2 to the laser 215-2 (e.g., via the application of a bias current), or the application of the frequency tone 218-2 to the EAM 216-2 (e.g., via the application of a bias voltage). It should be understood that although primarily presented with respect to a particular embodiment of the second IM transmitter 212-2 (i.e., including particular components arranged in a particular arrangement), the second IM transmitter 212-2 can be implemented in a variety of other ways (e.g., using a different sequence of components, using a different group of components, etc., as well as various combinations thereof), and therefore, the application of the frequency tone 218-2 to the optical channel at the second IM transmitter 212-2 can also be implemented in a variety of other ways.

[0042] ONU 220--1 includes a receiver 221--1. Receiver 221--1 includes a polarization controller 222--1, a polarization beam splitter (PBS) 223--1, a pair of DD receivers 224--1--1 and 224--1--2 (collectively referred to as DD receiver 224--1), and a polarization tracking controller 225--1. Polarization controller 222--1 receives a downstream optical signal, performs polarization control for polarization alignment of orthogonal polarization optical channels of the downstream optical signal, and provides the polarization-aligned downstream optical signal to PBS 223--1. PBS 223--1 receives the polarization-aligned downstream optical signal, splits the polarization-aligned downstream optical signal into a first optical channel based on a first polarization and a second optical channel based on a second polarization, and provides the first optical channel based on the first polarization to DD receiver 224--1--1 and provides the second optical channel based on the second polarization to DD receiver 224--1--2. DD receiver 224--1--1 recovers data transmitted by OLT 210 from a first optical channel based on a first polarization, and similarly, DD receiver 224--1--2 recovers data transmitted by OLT 210 from a second optical channel based on a second polarization. Receiver 221--1 is configured to support polarization tracking for an orthogonal polarization optical channel pair (e.g., for a downstream optical signal including a first optical channel based on a first polarization and a second optical channel based on a second polarization) based on either or both of frequency tones 218--1 and 218--2 applied to the optical channels at OLT 210.

[0043] The receiver 221--1 is configured to support polarization tracking for a pair of orthogonal polarization optical channels (e.g., for a downstream optical signal including a first optical channel based on a first polarization and a second optical channel based on a second polarization). The receiver 221--1 is configured to support polarization tracking for a pair of orthogonal polarization optical channels based on any one or both of the frequency tones 218 for SBS suppression at the transmitter 211. The DD receiver 224--1--1 includes an avalanche photodiode (APD) 226--1--1 and an analog-to-digital converter (ADC) 227--1--1, and any one or both of the frequency tones 218 can be extracted from any one or both of the APD 226--1--1 and the ADC 227--1--1 and provided to a polarization tracking controller 225--1 for controlling a polarization controller 222--1, which controls the alignment of polarizations of the orthogonal polarization optical channels of the downstream optical signal. DD receiver 224--1--2 receives APD 226--1--2 and ADC 227--1--2, and either or both of frequency tones 218 may be extracted from either or both of APD 226--1--2 and ADC 227--1--2 and provided to polarization tracking controller 225--1 for controlling polarization controller 222--1, which controls the alignment of polarizations of orthogonal polarization optical channels of downstream optical signals. Frequency tones 218 may be processed by polarization tracking controller 225--1 in various ways to support polarization tracking.

[0044] ONU 220--2 includes a receiver 221--2. Receiver 221--2 includes a polarization controller 222--2, a polarizer 223--2, a DD receiver 224--2, and a polarization tracking controller 225--2. Polarization controller 222--2 receives a downstream optical signal, performs polarization control for polarization alignment of orthogonal polarization optical channels of the downstream optical signal, and provides the polarization-aligned downstream optical signal to polarizer 223--2. Polarizer 223--2 receives the polarization-aligned downstream optical signal, and provides the first optical channel based on the first polarization or the second optical channel based on the second polarization to DD receiver 224--2. DD receiver 224--2 recovers data transmitted by OLT 210 from the first optical channel based on the first polarization or the second optical channel based on the second polarization. Receiver 221-2 is configured to support polarization tracking for an orthogonal polarization optical channel pair (e.g., for a downstream optical signal including a first optical channel based on a first polarization and a second optical channel based on a second polarization) based on one or both of frequency tones 218-1 and 218-2 applied to the optical channels at OLT 210.

[0045] The receiver 221--2 is configured to support polarization tracking for an orthogonal polarization optical channel pair (e.g., for a downstream optical signal including a first optical channel based on a first polarization and a second optical channel based on a second polarization). The receiver 221--2 is configured to support polarization tracking for an orthogonal polarization optical channel pair based on one or both of the frequency tones 218 for SBS suppression at the transmitter 211. The DD receiver 224--2 includes an avalanche photodiode (APD) 226--2 and an analog-to-digital converter (ADC) 227--2, and the frequency tone 218--1 can be extracted from either or both of the APD 226--1--1 and the ADC 227--1--1 and provided to a polarization tracking controller 225--1 for controlling a polarization controller 222--1, which controls the alignment of polarizations of the orthogonal polarization optical channels of the downstream optical signal. The frequency tone 218 can be processed by the polarization tracking controller 225--2 in various ways for supporting polarization tracking. It should be understood that although primarily presented with respect to example embodiments in which extraction of frequency tone(s) from optical channel(s) is performed in-band from one or more components supporting the optical channel(s), in at least some embodiments, extraction of frequency tone(s) may be performed out-of-band from components supporting the optical channels. For example, in an ONU 220--1 in which one or both of the optical frequencies are extracted from a first optical channel, an optical splitter may be disposed between a PBS 223--1 and a DD receiver 224--1--1 for splitting the optical signal and directing the optical signal to a monitoring APD (or other suitable component), which may extract the frequency tone(s) and provide the extracted frequency tone(s) to a polarization tracking controller 225--1 for controlling a polarization controller 222--1, which controls alignment of polarizations of orthogonal polarization optical channels of a downstream optical signal. For example, in an ONU 220--1 in which one or both of the optical frequencies are extracted from a second optical channel, an optical splitter can be arranged between a PBS 223--1 and a DD receiver 224--1--2 for splitting the optical signal and directing the optical signal to a monitoring APD (or other suitable component), which can extract (multiple) frequency tones and provide the extracted (multiple) frequency tones to a polarization tracking controller 225--1 for controlling a polarization controller 222--1, which controls the alignment of polarizations of orthogonal polarized optical channels of the downstream optical signal.For example, in ONU 220--2, an optical splitter may be arranged between polarizer 223--2 and DD receiver 224--2 for splitting the optical signal and directing the optical signal to a monitoring APD (or other suitable component), which may extract (multiple) frequency tones and provide the extracted (multiple) frequency tones to a polarization tracking controller 225--2 for controlling a polarization controller 222--2, which controls the alignment of polarizations of orthogonal polarization optical channels of the downstream optical signal. It should be understood that optical frequency tones may be extracted in various other ways.

[0046] It should be understood that although presented primarily with respect to example embodiments in which particular components are used to perform particular functions, in at least some embodiments, other types of components suitable for performing those functions may be used to perform the functions. For example, although presented primarily with respect to example embodiments in which particular types of components are used for optical-to-electrical conversion at the receiver (i.e., APDs such as APD 226--1 of ONU 220--1 and APD 226--2 of ONU 220--2), other suitable components may be used for optical-to-electrical conversion at the receiver (e.g., APD with transimpedance amplifier (APD--TIA), PIN photodiode, PIN--TIA optical receiver, etc., and various combinations thereof).

[0047] It should be understood that PON 200 illustrates only some of the ways in which frequency tones may be applied at the transmitter for SBS suppression and processed at the receiver for polarization tracking.

[0048] Figure 3 An example embodiment of a method for use by a transmitter to support backscatter mitigation in a PON configured to support joint backscatter mitigation and polarization tracking is shown. It should be understood that although primarily presented as a serial execution, at least a portion of the functionality of method 300 may be performed simultaneously or in different order. Figure 3 The method 300 is performed in the order presented. At box 301, the method 300 starts. At box 310, a first frequency tone is applied to a first optical channel based on a first polarization, and a second frequency tone is applied to a second optical channel based on a second polarization, wherein the first frequency tone and the second frequency tone are configured to support suppression of stimulated Brillouin scattering for transmission from a transmitter, wherein the first frequency tone and the second frequency tone are different. At box 320, the first optical channel and the second optical channel are propagated toward a receiver, wherein at least one of the first frequency tone or the second frequency tone is configured for use by the receiver for polarization tracking of at least one of the first optical channel or the second optical channel at the receiver. At box 399, the method 300 ends. It should be understood that the above description herein is not limited to the following. Figure 1A and Figure 1B ,as well as Figure 2Aand Figure 2B The various functions presented can be incorporated into Figure 3 In the context of method 300 .

[0049] Figure 4 An example embodiment of a method for use by a receiver to support polarization tracking in a PON configured to support joint backscatter mitigation and polarization tracking is shown. It should be understood that although primarily presented as a serial execution, at least a portion of the functionality of method 400 may be performed simultaneously or in different Figure 4 The method 400 is performed in the order presented. In box 401, the method 400 starts. In box 410, a first optical channel based on a first polarization and a second optical channel based on a second polarization are received from a transmitter. In box 420, at least one of a first frequency tone or a second frequency tone is extracted from at least one of the first optical channel or the second optical channel, wherein the first frequency tone and the second frequency tone are configured to support suppression of stimulated Brillouin scattering for transmission from the transmitter, wherein the first frequency tone and the second frequency tone are different. Used by a receiver for polarization tracking of at least one of the first optical channel or the second optical channel at the receiver. In box 430, polarization tracking of at least one of the first optical channel or the second optical channel is performed based on at least one of the first frequency tone or the second frequency tone. In box 499, the method 400 ends. It should be understood that the polarization tracking of at least one of the first optical channel or the second optical channel is performed based on the at least one frequency tone of the first frequency tone or the second frequency tone. In box 499, the method 400 ends. It should be understood that the above description herein is not limited to the above description. Figure 1A and Figure 1B ,as well as Figure 2A and Figure 2B The various functions presented can be incorporated into Figure 4 In the context of method 400 .

[0050] Various example embodiments for supporting joint SBS suppression and polarization tracking in a PON system may provide various advantages or potential advantages. For example, various example embodiments for supporting joint SBS suppression and polarization tracking in a PON system may be configured to support SBS suppression and polarization tracking on a per-channel basis using frequency tones for SBS suppression of transmissions from a transmitter and polarization tracking at a receiver. It should be appreciated that various example embodiments for supporting joint SBS suppression and polarization tracking in a PON system may provide various other advantages or potential advantages.

[0051] Figure 5 An example embodiment of a computer suitable for performing the various functions presented herein is shown.

[0052] The computer 500 includes a processor 502 (e.g., a central processing unit (CPU), a processor, a processor having a set of processor cores, a processor core of a processor, etc.) and a memory 504 (e.g., a random access memory (RAM), a read-only memory (ROM), etc.). In at least some example embodiments, the computer 500 may include at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the computer to perform various functions presented herein.

[0053] The computer 500 may also include a cooperating element 505. The cooperating element 505 may be a hardware device. The cooperating element 505 may be a process that may be loaded into the memory 504 and executed by the processor 502 to implement the various functions presented herein (in which case, for example, the cooperating element 505 (including related data structures) may be stored on a non-transitory computer-readable medium, such as a storage device or other suitable type of storage unit (e.g., a magnetic drive, an optical drive, etc.)).

[0054] The computer 500 may also include one or more input / output devices 506. The input / output devices 506 may include one or more of a user input device (e.g., a keyboard, a keypad, a mouse, a microphone, a camera, etc.), a user output device (e.g., a display, a speaker, etc.), one or more network communication devices or elements (e.g., an input port, an output port, a receiver, a transmitter, a transceiver, etc.), one or more storage devices (e.g., a tape drive, a floppy disk drive, a hard disk drive, a high-density disk drive, etc.), etc., and various combinations thereof.

[0055] It should be understood that the computer 500 may represent a general architecture and functionality suitable for implementing the functional elements described herein, portions of the functional elements described herein, etc., and various combinations thereof. For example, the computer 500 may provide a general architecture and functionality suitable for implementing one or more elements presented herein. For example, the computer 500 may provide a general architecture and functionality suitable for implementing at least one of the following: one or more elements or portions or combinations thereof of an OLT, one or more elements or portions or combinations thereof of an ONU, etc.

[0056] It should be understood that at least some of the functionality presented herein may be implemented in software (e.g., by implementing the software on one or more processors for execution on a general-purpose computer (e.g., executed by one or more processors) to provide a special-purpose computer, etc.) and / or may be implemented in hardware (e.g., using a general-purpose computer, one or more application-specific integrated circuits, and / or any other hardware equivalents).

[0057] It should be understood that at least some of the functions presented herein can be implemented in hardware, for example, as circuits that cooperate with a processor to perform various functions. Some of the functions / elements described herein can be implemented as a computer program product, in which computer instructions, when processed by a computer, adjust the operation of the computer to invoke or otherwise provide the methods and / or techniques described herein. Instructions for invoking various methods can be stored in fixed or removable media (e.g., non-transitory computer-readable media), transmitted via a data stream in a broadcast or other signal-bearing medium, and / or stored in a memory within a computing device that operates according to the instructions.

[0058] It should be understood that the term "non-transitory" as used herein is a limitation on the medium itself (ie, tangible, not a signal), and not on the persistence of data storage (eg, RAM versus ROM).

[0059] It should be understood that, as used herein, “at least one of ” and “at least one of: ” and similar expressions, where a list of two or more elements is connected by “and” or “or”, refer to at least any one element, or at least any two or more elements, or at least all elements.

[0060] It should be understood that, as used herein, the term "or" refers to a non-exclusive "or" unless otherwise indicated (eg, with use of "otherwise" or "or in the alternative").

[0061] It will be appreciated that although various embodiments incorporating the teachings presented herein have been shown and described in detail, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.

Claims

1. A system comprising: a transmitter configured to apply a first frequency tone to a first optical channel based on a first polarization and to apply a second frequency tone to a second optical channel based on a second polarization, wherein the first frequency tone and the second frequency tone are configured to support suppression of stimulated Brillouin scattering for transmissions from the transmitter, wherein the first frequency tone and the second frequency tone are different; and A receiver is configured to utilize at least one of the first frequency tone or the second frequency tone for polarization tracking of at least one of the first optical channel based on the first polarization or the second optical channel based on the second polarization.

2. The system according to claim 1, wherein: The first frequency tone and the second frequency tone are within a range of frequency tones configured to support suppression of stimulated Brillouin scattering.

3. The system according to any one of claims 1 to 2, wherein: At least one of the first frequency tone or the second frequency tone is applied for amplitude modulation to support suppression of stimulated Brillouin scattering for transmission from the transmitter.

4. The system according to any one of claims 1 to 2, wherein: At least one of the first frequency tone or the second frequency tone is applied for phase modulation to support suppression of stimulated Brillouin scattering for transmission from the transmitter.

5. The system according to any one of claims 1 to 4, wherein: The first frequency tone is applied to at least one of: a digital-to-analog converter associated with the first optical channel, an electrical amplifier associated with the first optical channel, a laser associated with the first optical channel, an external modulator associated with the first optical channel, a phase modulator associated with the first optical channel, or an optical amplifier associated with the first optical channel.

6. The system according to any one of claims 1 to 4, wherein: The second frequency tone is applied to at least one of: a digital-to-analog converter associated with the second optical channel, an electrical amplifier associated with the second optical channel, a laser associated with the second optical channel, an external modulator associated with the second optical channel, a phase modulator associated with the second optical channel, or an optical amplifier associated with the second optical channel.

7. A system according to any one of claims 1 to 6, wherein: The transmitter comprises: a first frequency tone generator configured to generate the first frequency tone and apply the first frequency tone to the first optical channel; and A second frequency tone generator is configured to generate the second frequency tone and apply the second frequency tone to the second optical channel.

8. The system according to any one of claims 1 to 7, wherein: At least one of the first frequency tone or the second frequency tone is extracted from at least one of the first optical channel or the second optical channel.

9. The system according to any one of claims 1 to 8, wherein: At least one of the first frequency tone or the second frequency tone is extracted from at least one of an optical-to-electrical converter or an analog-to-digital converter.

10. The system according to any one of claims 1 to 9, wherein: The receiver is configured to utilize at least one of the first frequency tone or the second frequency tone for polarization tracking of at least one of the first optical channel or the second optical channel at the receiver.

11. The system according to any one of claims 1 to 10, wherein: The receiver is configured to generate a feedback signal for a polarization controller based on at least one of the first frequency tone or the second frequency tone, and to perform polarization tracking of at least one of the first optical channel or the second optical channel at the receiver based on the feedback signal for the polarization controller.

12. The system according to any one of claims 1 to 11, wherein: The receiver comprises: a polarization controller configured to perform polarization tracking for at least one of the first optical channel or the second optical channel; and A controller configured to generate a feedback signal based on at least one of the first frequency tone or the second frequency tone and provide the feedback signal to the polarization controller.

13. An apparatus comprising: A transmitter configured to: applying a first frequency tone to a first optical channel based on a first polarization and applying a second frequency tone to a second optical channel based on a second polarization, wherein the first frequency tone and the second frequency tone are configured to support suppression of stimulated Brillouin scattering for transmissions from the transmitter, wherein the first frequency tone and the second frequency tone are different; and The first optical channel and the second optical channel are propagated toward a receiver, wherein at least one of the first frequency tone or the second frequency tone is configured to be used by the receiver for polarization tracking of at least one of the first optical channel or the second optical channel at the receiver.

14. The device according to claim 13, wherein: The first frequency tone and the second frequency tone are within a range of frequency tones configured to support suppression of stimulated Brillouin scattering.

15. The device according to any one of claims 13 to 14, wherein: At least one of the first frequency tone or the second frequency tone is applied for amplitude modulation to support suppression of stimulated Brillouin scattering for transmission from the transmitter.

16. The device according to any one of claims 13 to 14, wherein: At least one of the first frequency tone or the second frequency tone is applied for phase modulation to support suppression of stimulated Brillouin scattering for transmission from the transmitter.

17. An apparatus comprising: A receiver configured to: receiving from a transmitter a first optical channel based on a first polarization and a second optical channel based on a second polarization; extracting at least one of a first frequency tone or a second frequency tone from at least one of the first optical channel or the second optical channel, wherein the first frequency tone and the second frequency tone are configured to support suppression of stimulated Brillouin scattering for transmissions from the transmitter, wherein the first frequency tone and the second frequency tone are different; and Polarization tracking of at least one of the first optical channel or the second optical channel is performed based on at least one of the first frequency tone or the second frequency tone.

18. The device according to claim 17, wherein: The first frequency tone and the second frequency tone are within a range of frequency tones configured to support suppression of stimulated Brillouin scattering.

19. The device according to any one of claims 17 to 18, wherein: The receiver is configured to utilize at least one of the first frequency tone or the second frequency tone for polarization tracking of at least one of the first optical channel or the second optical channel at the receiver.

20. The device according to any one of claims 17 to 19, wherein: The receiver is configured to generate a feedback signal for a polarization controller based on at least one of the first frequency tone or the second frequency tone, and to perform polarization tracking of at least one of the first optical channel or the second optical channel at the receiver based on the feedback signal for the polarization controller.

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