Optical service channel systems and methods over high loss links

Optical service channel (OSC) systems and methods over high loss links are described utilizing redundant telemetry channels. A first telemetry channel provides a low bandwidth communication channel used when Raman amplification is unavailable on a high loss link for supporting a subset of operations, administration, maintenance, and provisioning (OAM&P) communication. A second telemetry channel provides a high bandwidth communication channel for when Raman amplification is available to support full OAM&P communication. The first and second telemetry operate cooperatively ensuring nodal OAM&P communication over high loss links (e.g., 50 dB) regardless of operational status of Raman amplification.

FIELD OF THE INVENTION

Generally, the field of art of the present disclosure pertains to fiber optic systems and methods, and more particularly, to optical service channel (OSC) systems and methods over high loss links such as festoon applications.

BACKGROUND OF THE INVENTION

Conventionally, optical service channels or optical supervisory channels (collectively referred to as OSCs herein) provide a wavelength on a link between two nodes for data communications there between. That is, OSCs are an additional wavelength in a wavelength division multiplexing (WDM) system usually outside the erbium doped fiber (EDFA) amplification band (e.g., at 1510 nm, 1620 nm, 1310 nm or another proprietary wavelength). This data communications is generally for operations, administration, maintenance, and provisioning (OAM&P) functionality such as information about WDM signals on the link as well as remote conditions at the two nodes. Additionally, the OSCs can provide remote software upgrades, network management connectivity, user data channel connectivity, etc. ITU standards suggest that the OSC should utilize an Optical Carrier (OC) OC-3 signal structure, though some have opted to use a 100 megabit Ethernet or another signal format. Typically, OSCs have a set maximum link budget. For example, a standard small form factor pluggable (SFP)-based OSC with as an OC-3 at 1510 nm has a link budget of about 42 dB. While 42 dB covers a large majority of fiber links, it does not cover festoon applications, channel crossings, or other high loss link applications. These high loss link applications can include Raman amplification, however the presence of Raman amplifiers does not improve the link budget of a typical 1510 nm OC-3 OSC because of injected amplifier stimulated emissions (ASE). That is, the high loss link applications do not realize any improvements with the OSC even with the Raman amplifiers on, due to a large optical receiver bandwidth at the Receiver and the inability to reject the Raman ASE. Even if the OSCs were adapted to support Raman amplification, the OSCs would not support communication the high loss link applications if the Raman amplifiers were turned off. Additionally, conventional OSCs are typically a single point of failure thus an OSC failure cannot be distinguished from a link failure. This happens in high loss link applications because the signal power from the far end is indistinguishable from the locally generated Raman ASE. All of the foregoing presents difficult challenges in high loss link applications.

BRIEF SUMMARY OF THE INVENTION

In an exemplary embodiment, an optical system over a high loss link, includes a first node; a second node; an optical fiber link communicatively coupling the first node to the second node, wherein the optical fiber link includes a high loss link; a high bandwidth communication channel providing full operations, administration, maintenance, and provisioning (OAM&P) communication between the first node and the second node over the optical fiber link; a low bandwidth communication channel providing a subset of OAM&P communication between the first node and the second node over the optical fiber link; and a controller at each of the first node and the second node for operating concurrently and selecting between the high bandwidth communication channel and the low bandwidth communication channel based on a plurality of operational factors associated with the optical system. The high bandwidth communication channel and the low bandwidth communication channel operate in combination with one another based on the plurality of operational factors associated with the optical system. The plurality of operational factors can include presence of Raman gain in the optical fiber link, overall loss on the optical fiber link, and launch power of the high bandwidth communication channel. The optical system can further include Raman amplification on the optical fiber link; wherein the low bandwidth communication channel is configured to operate when the Raman amplification is not operational on the optical fiber link and when the high bandwidth communication channel cannot support losses on the optical fiber link.

The low bandwidth communication channel can be configured to coordinate and sequence diagnostic and calibration functions at the first node and the second node in conjunction with establishing the Raman amplification. The low bandwidth communication channel can be configured to communicate a low bandwidth status word to indicate status of the first node to the second node, optical time domain reflectometer (OTDR) trace data, and back reflection measurements. The low bandwidth communication channel can include two discrete tones with an adjustable modulation depth on a first wavelength. The high bandwidth communication channel can include a second wavelength configured to receive the Raman amplification, and wherein a narrow bandwidth receiver filter can be utilized to remove amplified spontaneous emissions in the second wavelength due to the Raman amplification. The second wavelength can be implemented through a pluggable optical module at each of the first node and the second node. Optionally, the low bandwidth communication channel and the high bandwidth communication channel can each propagate in a same direction over the optical fiber link. Alternatively, the low bandwidth communication channel and the high bandwidth communication channel each propagate in a different directions over the optical fiber link with the high bandwidth communication channel propagating counter to the low bandwidth communication channel and any payload channels on the optical fiber link. The low bandwidth communication channel can be utilized to provide an estimate of Raman gain associated with the Raman amplification by taking a difference of power associated with the low bandwidth communication channel with the Raman amplification off from difference of power associated with the low bandwidth communication channel with the Raman amplification on.

Optionally, the second node includes a first subsystem providing Raman wavelengths to the optical fiber link towards the first node; a second subsystem receiving a first wavelength for the low bandwidth communication channel; and a third subsystem receiving a second wavelength for the high bandwidth communication channel, wherein the second wavelength is terminated on a pluggable optical module and narrowband filtered prior to the pluggable optical module; and the first node includes a first subsystem monitoring the Raman wavelengths to the optical fiber link towards the second node; a second subsystem transmitting the first wavelength for the low bandwidth communication channel, wherein the first wavelength is further configured to provide optical time domain reflectometer (OTDR) functionality; and a third subsystem transmitting the second wavelength for the high bandwidth communication channel, wherein the second wavelength is created on the pluggable optical module. Alternatively, the second node includes a first subsystem providing Raman wavelengths to the optical fiber link towards the first node; a second subsystem receiving a first wavelength for the low bandwidth communication channel; and a third subsystem transmitting a second wavelength for the high bandwidth communication channel, wherein the second wavelength is created on a pluggable optical module and counter propagates relative to payload carrying signals on the optical fiber link; and the first node includes a first subsystem monitoring the Raman wavelengths to the optical fiber link towards the second node; a second subsystem transmitting the first wavelength for the low bandwidth communication channel, wherein the first wavelength is further configured to provide optical time domain reflectometer (OTDR) functionality; and a third subsystem receiving the second wavelength for the high bandwidth communication channel, wherein the second wavelength is terminated on the pluggable optical module and narrowband filtered prior to the pluggable optical module.\

In another exemplary embodiment, an optical node includes a Raman amplifier coupled to an external fiber span with high loss and providing counter propagating Raman pump wavelengths to the external fiber span via a first filter; a second filter providing a first communication channel to a first module, wherein the first communication channel includes a high bandwidth communication channel providing full operations, administration, maintenance, and provisioning (OAM&P) communication with a downstream node on the external fiber span; a third filter providing a second communication channel to a second module, wherein the second communications channel includes a low bandwidth communication channel providing a subset of OAM&P communication with the downstream node on the external fiber span; and a controller for operating concurrently and selecting between a high bandwidth communication channel and a low bandwidth communication channel based on a plurality of operational factors. The plurality of operational factors can include whether the Raman amplifier is operational, overall loss on the external fiber span, and launch power of the high bandwidth communication channel. The first communication channel can include a first wavelength modulated with two discrete tones with an adjustable modulation depth; and the second communication channel can include a second wavelength which is amplified by the counter propagating Raman pump wavelengths and narrowband filtered to remove any amplified spontaneous emissions from the counter propagating Raman pump wavelengths.

In yet another exemplary embodiment, an operational method for telemetry over a high loss optical link includes operating a low bandwidth channel with Raman amplification off on the high loss optical link; utilizing the low bandwidth channel to communicate a subset operations, administration, maintenance, and provisioning (OAM&P) data over the high loss optical link to enable turn up of the Raman amplification; when the Raman amplification is on, operating a high bandwidth channel on the high loss link; and utilizing the high bandwidth channel to communicate full OAM&P data over the high loss optical link. The operational method can further include operating the high bandwidth channel in a counter propagating manner from the low bandwidth channel; and transmitting the low bandwidth channel in a co propagating manner with payload channels on the high loss optical link. The operational method can further include narrowband filtering the high bandwidth channel to remove amplified spontaneous emissions from the Raman amplification. The operational method can further include operating the high bandwidth channel on the high loss link and having the Raman amplification turned off; and reverting to the low bandwidth channel upon loss of the Raman amplification.

DETAILED DESCRIPTION OF THE INVENTION

In various exemplary embodiments, the present disclosure provides optical service channel (OSC) systems and methods over high loss links such as festoon applications. Variously, the OSC systems and methods support a high bandwidth communication channel and a low bandwidth communication channel working together over high loss links such as links with span losses greater than 50 dB. The high bandwidth communication channel can use high gain forward error correction (FEC) and distributed Raman gain amplifier to support increased bandwidth relative to the low bandwidth communication channel. The low bandwidth communication channel operates on the same high loss span as the high bandwidth communication channel with limited performance when the distributed Raman gain amplifier is unavailable. The operations of the communication channels can be implemented in a state machine which provides communication between two nodes over a high loss span as long as there is fiber connectivity therebetween and regardless of whether Raman amplification is available. Advantageously, the OSC systems and methods enable a working telemetry channel in Raman enabled high loss links that can be used to 1) automate turn-up of Raman Amplifiers, 2) co-relate, isolate and trouble shoot faults, and 3) offer all the Raman safety features in the link. This removes the conventional requirement such as in existing festoon applications for manual intervention for some or all of these functions. Advantageously, the OSC systems and methods enable automation (e.g., through turn-up to shutdown) of high loss links reducing manually intervention requirements.

The low bandwidth communication channel can include use of a low bandwidth tone to allow signaling across the nodes at turn-up when the Raman amplifier is off. The tone can also be used to exchange a low bandwidth status word, to indicate the status of the nodes. The low bandwidth tone can also be used to enable and sequence diagnostic function such as OTDR trace, back reflection measurements, etc. Once the OTDR and other measurements are turned on, the Raman Amplifier can be enabled. This allows a higher capacity telemetry channel, i.e. the high bandwidth communication channel, to work across the link. The higher capacity telemetry channel operates within the Raman amplifier bandwidth and experiences gain from the Raman Amplifier. The high bandwidth communication channel includes a narrow bandwidth receiver filter to block the ASE from the Raman amplification to improve the link budget of the telemetry signals. If there is any service interruption that results in the shutdown of the Raman Amplifier, the communication between the nodes can revert to the low bandwidth communication channel.

Referring toFIG. 1, in an exemplary embodiment, a block diagram illustrates an optical system10for transmission of WDM signals over a high loss link12. The optical system10includes two nodes14,16interconnected optically via the high loss link12. For example, the high loss link12can be a festoon fiber optic link with losses above 50 dB. For illustration purposes,FIG. 1shows a unidirectional link in the high loss link12without showing additional components at each of the nodes14,16such as transceivers, client equipment, etc. That is,FIG. 1book ends the optical system between optical amplifiers to illustrate the OSC systems and methods. The node14is the transmit side and the node16is the receive side. The high loss link12is bookended by Raman amplifiers18,20at the nodes14,16respectively, and EDFAs22,24are also shown coupled to the Raman amplifiers18,20respectively. From a signal propagation perspective, WDM signals (not shown) are transmitted through the EDFA22and the Raman amplifier18over the high loss link12to the Raman amplifier20and the EDFA24. The Raman amplifier20can provide counter propagating Raman amplification over the high loss link12. Optionally, the Raman amplifier18can provide co propagating Raman amplification over the high loss link12.

From an OSC/telemetry perspective, the optical system10includes two OSC/telemetry signals. As described herein, the OSC systems and methods relate to communications between two nodes across high loss links. The OSC systems and methods can refer to OSCs (i.e., optical service channel or optical supervisory channel), telemetry channels, communications channels, management channels, etc. all for the same functionality of a signal that enables communication between the nodes14,16over the high loss link12. In various exemplary embodiments, the optical system10supports two telemetry channels26,28between the nodes14,16that are tapped in/out prior to the EDFAs22,24. The two telemetry channels26,28can be referred to as a low bandwidth communication channel (i.e., a 15XX telemetry/optical time domain reflectometer (OTDR) channel26) and a high bandwidth communication channel (i.e., an OSC28) that work in conjunction with one another. As described herein, 15XX is a wavelength between 1500 nm and 1599 nm, i.e. XX equals 00-99. In practical embodiments, 15XX for the channels26,28will generally exclude the EDFA amplification band (e.g., 1535-1560 nm) as this is typically used for WDM signals.

The channel26can be the low bandwidth communication channel that is also configured to perform OTDR functionality through the Raman amplifier18as well as to monitor Raman amplification gain. The channel26is created by a 15XX telemetry/OTDR transceiver30at the node14which is inserted into a line associated with the high loss link12and the Raman amplifier18via a 15XX filter32. For example, the channel26can be a 1527 nm wavelength, and the filter32can be a coarse filter combining the 1527 nm wavelength with a broadband range of wavelengths such as 1530-1565 nm. Thus, the filter32is configured to selectively insert the channel26into the high loss link12. The channel26is received at the node16and selectively removed by a 15XX filter34that performs substantially the opposite functionality of the filter32. Finally, the channel26is received at a transceiver36for demodulation of any information modulated on the channel26. For example, the channel26can be modulated with an analog modulated (AM) tone, such as two discrete tones. The tone can be enabled only when the span loss is greater than a certain threshold and straightforward power detection is not reliable. The channel26is used to establish a low data rate between the two nodes14,16that will work for very high span losses without requiring Raman amplification. Further, the modulation depth of the tone can be changed based on operating condition of the optical system10. For example, the modulation depth can be high, before the Raman amplifiers18,20are turned off and there is no traffic across the link. The modulation depth is reduced after the Raman amplifiers18,20are turned on and there is traffic on the link. This reduces cross talk from the tone on the WDM payload channels. Also, the tone can be turned off if the high loss link12can support OSC28with the Raman amplifiers18,20are turned off. Also, in addition to providing the low bandwidth tones, the transceiver30can be used for OTDR and for monitoring Raman gain over the high loss link12.

Concurrent with the channel26, the optical system10can include the OSC28which can be a separate OSC wavelength (e.g., an OC-3 SFP pluggable module) that is used for the high bandwidth communication channel such as when the Raman amplifiers18,20are on or where supported without the Raman amplifiers18,20being on. The OSC28is created by 15XX OSC TX38at the node14which is inserted into a line associated with the high loss link12and the Raman amplifier18via a 15XX filter40. For example, the OSC28can be a 1517 nm wavelength (or any other wavelength), and the filter40can be a coarse filter combining the 1517 nm wavelength with a broadband range of wavelengths such as 1530-1565 nm. Thus, the filter40is configured to selectively insert the OSC28into the high loss link12. Collectively, the filters32,34,40,42can be referred to as coarse WDM filters which are configured to add/drop wavelengths out of the EDFA amplification band (e.g., 1530-1565 nm) with the EDFA amplification band. The OSC28is received at the node16and selectively removed by a 15XX filter42that performs substantially the opposite functionality of the filter40. Finally, the OSC28is received at a receiver44for demodulation of any information modulated on the OSC28.

The channels26,28can in principle be at the same wavelength. In an exemplary embodiment of the OSC systems and method, separate wavelengths are used by the channels26,28to allow for redundancy in link monitoring and also preserving a legacy OSC link (CWDM SFPs with CWDM drop filters). There are other possible benefits to having two different wavelengths for the channels26,28to besides providing redundancy. First, as discussed herein, the channels26,28can be used to provide an estimate of Raman gain of the Raman amplifiers18,20. In an exemplary algorithm, fiber loss of the high loss link12can be set at a baseline with the Raman amplifiers18,20off Once the Raman amplifiers18,20are activated, the different in loss can be used to estimate Raman gain of the Raman amplifiers18,20. For example, the channel26can be received at a first power level with the Raman amplifiers18,20off and a second power level with the Raman amplifiers18,20on; the difference being indicative of gain associated with the Raman amplifiers18,20. Also, differential loss measurements could be used to distinguish if the change in the apparent loss of the high loss link12is due to change in distributed Raman Amplifier gain or change in fiber loss. One of the wavelengths of the channels26,28can be selected so that the Raman gain is low or zero, while the other wavelength of the channels26,28is selected so that the Raman gain is high. The differential loss change at the two wavelengths can be used to estimate if the loss change was primarily due to change in the fiber loss of change in Raman gain of the amplifier.

In another exemplary embodiment of the optical system10, the channels26,28can be propagating in opposite directions. For example, the channel26can be a co-propagating tone with WDM wavelengths and the OSC28can be counter or backward propagating relative to the channel26and the WDM wavelengths. The counter propagating OSC28would solve some of the issues described in the previous sections. For example, cross talk from OSC modulation impacts coherent WDM channels when they are co-propagating in the high loss link12. However, if the OSC28is counter propagating, there is a large walk off between the OSC28and the WDM channels. Thus, the launch power of the OSC28channels can be increased significantly. Also, the OSC28can take advantage of Raman Gain. In the counter propagating embodiment, the impact of Raman ASE is minimal, because the amplification happens at the beginning of the high loss link12, rather than at the end of the high loss link12, where the OSC28power is low. One of the benefits of a counter propagating (i.e., backward propagating) OSC (especially one with a low bandwidth like the OSC compared to the payload channels), is that the non-linear cross-talk is negligible due to the quick walk-off. Also, bi-directional OSC channels, i.e. the counter propagating OSC channel28and the channel26, also has an advantage in reducing the time required for safety shutdown such as when there is both forward and backward propagating Raman amplifiers.

Referring toFIG. 2, in an exemplary embodiment, a flow chart illustrates an operational method50associated with the channels26,28in the optical system10. The channels26,28can operate together ensuring there is communication between the nodes14,16regardless of an operational state of the Raman amplifiers18,20. An objective of the operational method50is to ensure there is communication between the two nodes14,16of the optical system10. In the context of the operational method50, the channel26can be referred to as a low bandwidth channel, and the channel28can be referred to as a high bandwidth channel. Further, the operational method50can continuously operate as long as the optical system10is operational, and the operational method50can be initiated at any of the steps. If Raman gain is not off (step52), then the operational method50can utilize the high bandwidth channel (step54). If the Raman gains is off (step52) and loss on the high loss span12is not too high for the OSC (step56), then the operational method50can utilize the high bandwidth channel (step54). If the loss is too high for the OSC (step56), then the operational method50can utilize the low bandwidth channel (step58). The operational method50can continue to utilize the low bandwidth channel until Raman gain is on (step60) and then utilize the high bandwidth channel.

The low bandwidth channel is used for setup and turn up of the high loss link12. That is, the low bandwidth channel includes low bandwidth that would work in the absence of Raman gain. Generally, the low bandwidth channel is used to coordinate and sequence diagnostic and calibration functions at the two nodes14,16. That is, the low bandwidth channel is generally a reduced bandwidth OAM&P channel focused on limited functions to enable turn up of the Raman amplifiers18,20and the like. As described herein, the low bandwidth channel can use tones with a settable modulation depth to take advantage of the Raman gain in the system10. As shown in the operational method20, the low bandwidth channel is activated in event of a Raman shutdown for recovery in the system10. The high bandwidth channel has increased bandwidth from the low bandwidth channel and is configured to operate with the Raman gain available (or without if supported with the reach). In an exemplary embodiment, the high bandwidth channel is an out-of-band signal such as a 1510 nm OC-3. In another exemplary embodiment, the high bandwidth channel could be a WDM channel. It is expected that the high bandwidth channel supports full OAM&P functionality between the nodes14,16whereas the low bandwidth channel supports a reduced subset of OAM&P functionality.

Also, as described herein, the high bandwidth channel can be counter propagating with respect to the payload channels to improve link budget. The low bandwidth channel can use tone channels at a single source with a variable data rate. Further, the low bandwidth channel and the high bandwidth channel can be different wavelengths with separate transmitters and receivers. This improves reliability, by providing redundant means to verify link continuity with the Raman gain present, provides an ability to estimate measurements of the fiber loss and Raman gain, and differential power measurements at the two wavelengths can be used to isolate problems with changes in fiber loss and Raman Gain.

Referring toFIG. 3, in an exemplary embodiment, a block diagram illustrates an exemplary implementation of the Raman amplifiers16,18for use in the optical system10. The Raman amplifiers16,18support two fibers, A and B, and in context of the optical system10, the Raman amplifier16uses the A fiber and associated components and the Raman amplifier18uses the B fiber and associated components. Of course, there can be a second fiber in the optical system10(not shown) where the Raman amplifier16uses the B fiber and associated components and the Raman amplifier18uses the A fiber and associated components. The Raman amplifier16,18can be grouped into three internal subsystems102,104,106, namely a pump subsystem102, an OTDR-TG (Telemetry Gain) subsystem104, and an OSC subsystem106. Of course, other configurations of the Raman amplifier16,18are also contemplated herein. For example, the functionality of the subsystems102,104,106can be integrated into a single system. Those of ordinary skill in the art will recognize that the Raman amplifier16,18is presented as an exemplary embodiment, and the OSC systems and methods described herein contemplate use with any embodiment of a Raman amplifier.

Also, it should be appreciated by those of ordinary skill in the art that the amplifier16,18is depicted in an oversimplified manner, and a practical embodiment may include additional components and suitably configured processing logic to support known or conventional operating features that are not described in detail herein. Generally, the pump subsystem102is configured to provide the Raman amplification into the high loss link12, the OTDR-TG subsystem104is configured to provide OTDR functionality and the functionality of the telemetry channel26, i.e. the low bandwidth channel, and the OSC subsystem106is configured to provide the functionality of the OSC28, i.e. the high bandwidth channel. The functionality and the components associated with each of these subsystems102,104,106is now described from the perspective of the A and B fibers.

With respect to the A fiber, the Raman amplifier16,18includes an Ainport110which receives signals from an external fiber such as the high loss link12. In the optical system10, the Ainport110is where the high loss link12connects to the Raman amplifier18at the node16. A 14XX/1550 WDM filter112receives the Ainport110and is configured to send WDM wavelengths (e.g., 1500 and above) to a Raman gain flattening filter (GFF)114and simultaneously combine 14XX Raman pump wavelengths from a Raman pump subsystem116. The 14XX Raman pump wavelengths are counter propagating to the WDM wavelengths. A small power tap118(e.g., 1-5%) can couple a portion off the connection of the Raman pump subsystem116to the 14XX/1550 WDM filter112to monitor for Raman back reflections (BR) via a BR monitor120. An optical power monitor (OPM)122can also monitor an output of the A fiber.

The Raman GFF114is configured to flatten the spectrum of the various WDM signals following the Raman amplification in the external fiber. The Raman GFF114connects to an OTDR-TG WDM filter124in the OTDR-TG subsystem104. The WDM filter124is configured to separate the WDM wavelengths (e.g., 1530-1565 nm) from the telemetry channel26wavelength. As described herein, in an exemplary embodiment, the telemetry channel26wavelength can be 1527 nm. The OTDR-TG subsystem104includes an OTDR-TG receiver (RX)126coupled to the WDM filter124. The OTDR-TG RX126is configured to receive the telemetry channel26wavelength and for the low bandwidth signal, demodulate any tones on the telemetry channel26wavelength. The WDM filter124also connects to an OSC filter128in the OSC subsystem106. The OSC filter128is configured to split out the OSC channel28from the WDM wavelengths, i.e. similar functionality to the WDM filter124.

An output of the OSC filter128for the WDM wavelengths connects to a small power tap130which taps off a portion of output power but provides the majority of the output power to an Aoutport132out of the Raman amplifier16,18. An output of the OSC filter128for the OSC28connects to a small power tap134which provides a small amount of power to an OSC monitor136. The majority of optical power from the power tap134connects to an OSCoutport138which connects to a receiver on an SFP module140. Thus, the OSC28is formed through a DWDM SFP pluggable module or other types of pluggable modules. The OSC subsystem106also includes a back reflection (BR) monitor142and a splitter (3 dB)144coupled to the power tap130. The BR monitor142can check for any back reflections from the Aoutport132. The splitter144connects to the OPM122and to another splitter146which connects to a signal monitor148and an external monitor port150. The OSC subsystem106also includes an OSC module152coupled to the SFP140. The OSC module152includes various opto-electronic components for processing of the OSC28.

With respect to the B fiber, the Raman amplifier16,18includes an Boutport160which outputs signals to an external fiber such as the high loss link12. In the optical system10, the Boutport160is where the high loss link12connects to the Raman amplifier16at the node14. The Boutport160is connected to another 14XX/1550 WDM filter162which splits off the 14XX bandwidth to a Raman leakage monitor164. The 14XX/1550 WDM filter162is connected to another OTDR-TG WDM filter168which splits combines the telemetry channel26from an OTDR-TG transmitter (TX)170with other wavelengths (e.g., WDM wavelengths and the OSC28). The OTDR-TG TX170is configured to transmit the channel26with the tones modulated thereon. The OTDR-TG TX170can also transmit a wavelength for the channel26to perform OTDR functionality.

The OTDR-TG WDM filter168is connected to another OSC filter172in the OSC subsystem106. The OSC filter172combines the OSC28with WDM signals. For example, the WDM signals can be input through a Binport174which connects to a small power tap176. The majority of the output power from the power tap176is sent to the OSC filter172and smaller portions are provided to a back reflection (BR) monitor178and a splitter180. The BR monitor178can be configured to check for back reflections from the Binport174. The splitter180connects to a signal monitor182and an external monitor port18. The SFP140provides the OSC28to an OSC input port186on the OSC subsystem106where it is connected to a small power tap188which taps a small portion of power to an OSC monitor190and provides the majority of power to the OSC filter172.

Referring toFIG. 4, in an exemplary embodiment, a block diagram illustrates operation of the OSC28channel in the OSC systems and methods. In context of the OSC systems and methods, it is desirable for the OSC28to support Raman amplification from the Raman amplifiers16,18to support the high loss link12.FIG. 4illustrates various techniques applied to the OSC28to support the high loss link12. First, as described inFIG. 3, the OSC28can be implemented through a DWDM SFP or equivalent. Such a module has formatting and launch power applicable to high loss applications. Also, DWDM SFP modules are available with high gain FEC and even with impairment mitigation built in (e.g., chromatic dispersion compensation). The OSC28can be inserted at the node14using a conventional CWDM filter. With the use of a DWDM SFP, it is expected that the OSC28receives Raman gain similar to the WDM payload channels on the high loss link12. At the node16, the OSC28is dropped and includes broadband ASE noise (see graph200inFIG. 4).

The OSC monitor136can be used to detect total power of the OSC28. Next, the OSC28can be provided to an external narrowband filter202. For example, assuming the OSC28and the DWDM SFP are at 1517 nm, the external narrowband filter202can remove the broadband ASE noise and provide the OSC28as shown in graph204. The external narrowband filter202can be the OSC filter128or another filter. Following the external narrowband filter202, the OSC28is provided to the SFP140for termination thereof. In an exemplary embodiment, the SFP140can be a custom DWDM SFP and the external narrowband filter202can be separate from the OSC filter128(which can be referred to as a CWDM filter). The external narrowband filter202is used after the CWDM filter to reject the Raman ASE from the OSC28channel.

Additionally, the Raman amplifier16,18can include a controller180communicatively coupled to the OSC152, the OTDR-TG RX126, and the OTDR-TG TX170. The controller can be configured for operating concurrently and selecting between the high bandwidth communication channel and the low bandwidth communication channel based on a plurality of operational factors associated with the optical system. In conjunction with the optical system10, the nodes12,14, and the operational method50, it will be appreciated that some exemplary embodiments described herein may include one or more generic or specialized processors (“one or more processors”) such as microprocessors, digital signal processors, customized processors, and field programmable gate arrays (FPGAs) and unique stored program instructions (including both software and firmware) that control the one or more processors to implement, in conjunction with certain non-processor circuits, some, most, or all of the functions of the methods and/or systems described herein. Alternatively, some or all functions may be implemented by a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in which each function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the aforementioned approaches may be used. In an exemplary embodiment, the aforementioned components can generally be referred to as the controller180at each of the nodes12,14for operating concurrently and selecting between the high bandwidth communication channel and the low bandwidth communication channel based on a plurality of operational factors associated with the optical system.

Moreover, some exemplary embodiments may be implemented as a non-transitory computer-readable storage medium having computer readable code stored thereon for programming a computer, server, appliance, device, etc. each of which may include a processor to perform methods as described and claimed herein. Examples of such computer-readable storage mediums include, but are not limited to, a hard disk, an optical storage device, a magnetic storage device, a ROM (Read Only Memory), a PROM (Programmable Read Only Memory), an EPROM (Erasable Programmable Read Only Memory), an EEPROM (Electrically Erasable Programmable Read Only Memory), Flash memory, and the like. When stored in the non-transitory computer readable medium, software can include instructions executable by a processor that, in response to such execution, cause a processor or any other circuitry to perform a set of operations, steps, methods, processes, algorithms, etc.