Multi-wavelength transponder with wavelength division multiplexing modules

According to one embodiment, a system for transmitting an optical signal comprises a traffic distribution circuit configured to distribute traffic to a plurality of wavelength division multiplexer (WDM) modules. The system further comprises a first WDM module and a second WDM module. The first and second WDM modules each comprise a plurality of tunable optical transmitters, with each transmitter associated with a different wavelength band of a plurality of wavelength bands. Each transmitter in the first and second WDM modules is also tuned to transmit optical signals in channels included within the associated wavelength band of the transmitter. The first and second WDM modules each comprise a multiplexer configured to combine the optical signals transmitted from the plurality of transmitters into optical signals. The system further comprises a cyclic multiplexer configured to combine the optical signals from the first and second WDM modules into an optical output signal.

TECHNICAL FIELD

The present disclosure relates generally to optical communication networks and, more particularly, to a method and system for transmitting optical signals using wavelength division multiplexing (WDM) modules.

BACKGROUND

Telecommunications systems, cable television systems and data communication networks use optical networks to rapidly convey large amounts of information between remote points. In an optical network, information is conveyed in the form of optical signals through optical fibers. Optical fibers comprise thin strands of glass capable of communicating the optical signals over long distances with very low loss. Optical networks often employ wavelength division multiplexing (WDM) or dense wavelength division multiplexing (DWDM) to increase transmission capacity. In WDM and DWDM networks, a number of optical channels are carried in each fiber at disparate wavelengths, thereby increasing network capacity.

In WDM and DWDM networks, optical transmitters transmit the optical signals at the optical channels such that each channel corresponds with a transmitter. As the number of required channels increases, the number of required transmitters increases. Also, as the number of transmitters increases the likelihood that one of the transmitters may fail increases. Traditionally, replacing transmitters can be complicated and expensive, but building high quality transmitters to reduce the incidence of failure is also expensive.

SUMMARY

In accordance with the present disclosure disadvantages and problems associated with implementing a reduced cost optical transponder for transmitting wavelength division multiplexed optical signals may be reduced.

In accordance with one embodiment of the present disclosure, a system for transmitting an optical signal using a plurality of wavelength bands, with each wavelength band including a plurality of channels, comprises a traffic distribution circuit configured to distribute traffic to a plurality of wavelength division multiplexer (WDM) modules. The system further comprises a first WDM module. The first WDM module comprises a first plurality of tunable optical transmitters, each transmitter associated with a different wavelength band of the plurality of wavelength bands. Each transmitter is also tuned to transmit optical signals in a first channel included within the associated wavelength band of the transmitter. The first WDM module further comprises a first multiplexer coupled to the first plurality of transmitters and configured to combine the optical signals transmitted from the first plurality of transmitters into a first optical signal. The system also comprises a second WDM module that comprises a second plurality of tunable optical transmitters. Each transmitter in the second WDM module is associated with a different wavelength band of the plurality of wavelength bands and tuned to transmit optical signals in a second channel included within the associated wavelength band of the transmitter. The second WDM module also comprises a second multiplexer coupled to the second plurality of transmitters and configured to combine the optical signals transmitted from the second plurality of transmitters into a second optical signal. The system further comprises a cyclic multiplexer coupled to the first and second WDM modules and configured to combine the first and second optical signals into an optical output signal.

In accordance with another embodiment, a method for transmitting an optical signal using a plurality of wavelength bands, with each wavelength band including multiple channels, comprises distributing, by a traffic distribution circuit, traffic to a plurality of wavelength division multiplexing (WDM) modules. The method further comprises tuning a first plurality of tunable optical transmitters included in a first WDM module to a first channel included within each of the plurality of wavelength bands. Each transmitter in the first WDM module is associated with a different wavelength band of the plurality of wavelength bands. The method further comprises transmitting, by the first plurality of transmitters, optical signals in the first channels and combining, by a first multiplexer coupled to the first plurality of transmitters, the optical signals transmitted from the first plurality of transmitters into a first optical signal. The method also comprises tuning a second plurality of tunable optical transmitters included in a second wavelength division multiplexing (WDM) module to a second channel included within each of the plurality of wavelength bands. Each transmitter included in the second WDM module is associated with a different wavelength band of the plurality of wavelength bands. The method further comprises transmitting, by the second plurality of transmitters, optical signals in the second channels and combining, by a second multiplexer coupled to the second plurality of transmitters, the optical signals transmitted by the second plurality of transmitters into a second optical signal. Additionally, the method comprises combining, by a cyclic multiplexer coupled to the first and second WDM modules, the first and second optical signals into an optical output signal.

DETAILED DESCRIPTION

Embodiments of the present disclosure and its advantages are best understood by referring toFIGS. 1-15, where like numbers are used to indicate like and corresponding parts.

FIG. 1illustrates an example system100comprising a plurality of modular transponders102configured to interface wavelength division multiplexer (WDM) modules104. As described below, each module is configured to transmit optical traffic at particular optical channels of a band of optical wavelengths.

Transponders102may be included in any optical network. Optical networks may comprise a plurality of optical components configured to transmit information between each other using optical signals. Optical networks may include fibers configured to transport one or more optical signals communicated by components of the optical network.

Optical networks may transmit optical signals at specific wavelengths or channels. Each channel may be configured to carry a certain amount of information along fibers. To increase the information carrying capabilities of an optical network, multiple optical signals transmitted at multiple channels may be combined into a single optical signal that may be transmitted via a single fiber.

The process of communicating information at multiple channels of a single optical signal is referred to in optics as wavelength division multiplexing (WDM). Dense wavelength division multiplexing (DWDM) refers to the multiplexing of a larger (denser) number of wavelengths, usually greater than forty, into a fiber. WDM, DWDM, or other multi-wavelength transmission techniques are employed in optical networks to increase the aggregate bandwidth per optical fiber. Without WDM or DWDM, the bandwidth in networks would be limited to the bit rate of solely one wavelength.

Optical networks comprise optical transmitters configured to transmit optical signals at specific channels. Each channel may correspond with a different transmitter. Therefore, the more channels used by an optical network, the more transmitters that network requires. As the bandwidth and channel requirements of optical networks increase, the number of required transmitters also increases. However, as the number of transmitters increases, the likelihood that one of the transmitters may fail also increases.

Replacing individual transmitters can be complicated and costly. Traditionally, to reduce the likelihood of transmitter failure in systems that utilize many transmitters (e.g., DWDM systems), transmitters may be built to exacting standards. However, transmitters built to exacting specifications are expensive and implementing systems that utilize many transmitters can be cost prohibitive. Further, because each transmitter corresponds to a different channel and consequently transmits at a different wavelength, replacing individual transmitters may require ordering a specialized transmitter, or at the least, manufacturing and having on hand many different transmitters.

Therefore, a method and system for easily replacing and bypassing failed, standard transmitters may be advantageous for lowering costs and implementing more efficient optical systems. Having a small number of different tunable transmitters that may transmit optical signals at various channels may reduce the need for specific transmitters transmitting at specific channels, thus simplifying replacement of failed transmitters. Easy to replace, interchangeable transmitters may lower the cost of replacing failed transmitters. Further, transmitters with lower replacement costs may be manufactured according to less stringent specifications and may be manufactured at a lower cost. Even if the transmitters fail at a higher rate, the cost of replacing an inexpensive, easy to replace transmitter may be lower than implementing a system with expensive transmitters manufactured according to stringent standards.

Referring back toFIG. 1A, transponders102may be configured to interface easily interchangeable and replaceable, low cost, pluggable WDM modules104to reduce the costs associated with implementing transmitters in optical systems. WDM modules104may comprise any system device or apparatus configured to transmit optical signals within an optical network. Transponders102may include a plurality of slots (not expressly shown) configured to receive WDM modules104, with each slot configured to receive a different WDM module104.

Each slot and pluggable WDM module104may include optical interfaces that correspond with each other. Accordingly, the optical interface associated with the slot may be configured to couple to the optical interface associated with the WDM module104to allow for transponder102to be optically coupled to, and optically interface with, each WDM module104inserted into each slot. The optical interfaces between the slots and WDM modules104may allow for optical connections that may not require optical fibers, thus facilitating the insertion and removal of WDM modules104with respect to transponder102.

Additionally, each slot and pluggable WDM module104may include electrical interfaces that correspond with each other and located on the same end as the optical interfaces. The electrical interface associated with the slot may be configured to couple to the electrical interface associated with the WDM module104to allow for transponder102to be electrically coupled to, and electrically interface with, each WDM module104inserted into each slot. Having the electrical and optical interfaces located on the same end may also allow for easy insertion and removal of WDM modules104with respect to transponder102.

Each WDM module104may include a plurality of tunable optical transmitters. The transmitters may be tuned to transmit optical signals at specific channels and WDM modules104may be configured to wavelength division multiplex the optical signals into a single optical signal.

Each WDM module104may be identical to the other WDM modules104. Because the transmitters in each WDM module104are tunable to transmit at multiple wavelengths, the need for individual, channel specific transmitters may be reduced. Thus, the individual transmitters in each WDM module104may be configured to transmit optical signals at the same channels as the individual transmitters in other WDM modules104. Having one interchangeable WDM module104may lower costs due to only having to manufacture one type of WDM module to replace a WDM module with one or more failed transmitters instead of needing a specific replacement transmitter for a failed transmitter.

FIG. 1Bdepicts an example embodiment of a WDM module104that may interface with transponder102. WDM modules104and the slots of transponder102may be configured to allow easy insertion and removal of WDM modules104, thus facilitating replacement of a WDM module104if a transmitter within the WDM module104fails. Accordingly, both labor and network unavailability costs associated with replacing WDM modules104may be relatively low compared to traditional methods and systems for replacing failed transmitters.

The transmitters within WDM modules104may comprise simpler, less expensive transmitters than transmitters used in other systems. The ease of replacing WDM modules104may require less labor and easier steps compared to replacing transmitters in other systems. Accordingly, transmitter failure in a WDM module104may also require less labor and maintenance costs, thus reducing the need to utilize expensive transmitters manufactured at very high standards.

As described below with respect toFIG. 2, transponders102may also be configured to combine the optical signals of each WDM module104associated with the transponders into a single optical output signal transmitted out of one or more optical output ports106to a fiber108. Transponders102may also include one or more input ports110optically coupled to a fiber108and configured to receive the optical signals transmitted from another transponder102. Transponders102may comprise one or more optical receivers (not expressly shown) configured to receive the optical input signals from an input port110. Fibers108may comprise any suitable type of fiber for carrying optical signals, such as a Single-Mode Fiber (SMF) or Multi-Mode Fiber (MMF).

Transponders102may also include one or more electrical input ports (not expressly shown) configured to receive electrical signals that may be converted to optical signals, by the transmitters included within WDM modules104, to be transmitted through optical output port106.

The plurality of WDM modules104included in transponders102may include spare WDM modules104and active WDM modules104. Spare and active WDM modules104may comprise the same standard WDM modules104, but may perform different functions. Initially, transponders102may send electrical signals for optical transmission over active channels associated with the transmitters within active WDM modules104. However, if the active channel fails (e.g., a transmitter within an active WDM module104fails), transponders102may send the electrical signals that were going to the transmitter associated with the failed channel to a spare transmitter in a spare WDM module104associated with a spare channel. Accordingly, the signals are being sent over a spare channel associated with the spare transmitter instead of to the transmitter associated with the failed channel.

Channels commonly fail due to the failure of the transmitters associated with the channels. Therefore the present disclosure discusses failure of transmitters specifically. However, the present disclosure should not be limited to such. Although failures of transmitters are extensively described, it should be understood that any failure of a channel due to any other factor, such as a down receiver, another component associated with the channel, etc., may cause transponders102to switch from a transmitter associated with the failed channel to a transmitter associated with a spare channel

Without spare WDM modules104, an active WDM module104may need to be replaced upon failure of any transmitter included in the active WDM module104to maintain the bandwidth of the system and prevent loss of data being sent over the failed channel associated with the failed transmitter. However, with spare WDM modules104having transmitters associated with spare channels, multiple channels associated with transmitters in multiple active WDM modules104may fail before an active WDM module104with one or more transmitters associated with failed transmitters may need to be replaced. Thus, spare WDM modules104may reduce the number of maintenance and replacement visits, which may further reduce costs.

WDM modules104may also include an indicator112. Indicator112may indicate when the WDM module104associated with the indicator has a transmitter associated with a failed channel (e.g., a failed transmitter). Thus, indicator112may further facilitate replacement of WDM modules104by easily identifying those modules that need to be replaced. The indicators may indicate a required or preferred replacement sequence, or a level of urgency of replacement. Indicator112may comprise any system, apparatus or device that may indicate that a module104includes a failed transmitter. In some embodiments indicator112may comprise a light emitting diode (LED) or any other suitable device. In some embodiments, indicator112may indicate that a transmitter has failed, but not specify which transmitters have failed. In other embodiments, indicator112may indicate which transmitters204have failed, how many transmitters204have failed or both. Indicators may also indicate additional information such as time to expected failure and other characteristics of the WDM module.

Additions, modifications or omissions may be made toFIGS. 1A and 1Bwithout departing from the scope the present disclosure. For example, system100may include any number of transponders102and not just the two transponders102depicted. Further, each transponder102may include more or fewer WDM modules104than those depicted. The number of WDM modules104and transponders102may depend on the limitations and requirements of the system100being implemented.

FIG. 2illustrates an example transponder102comprising a plurality of WDM modules104in further detail. Transponder102may include a Serializer/DeSerializer Switch (SerDes Switch)202, a plurality of WDM modules104that may each include a plurality of tunable optical transmitters (Tx)204and a multiplexer206. Transponder102may further include power monitors208coupled to the outputs of WDM modules104and a cyclic multiplexer210. Cyclic multiplexer210may include output106and offset outputs214. Transponder102may also include a controller216.

SerDes Switch202may be any apparatus, system or device configured to receive a serial signal and transmit that signal among parallel outputs. In the present embodiment, SerDes Switch202may be configured to receive one or more electrical input signals and transmit those electrical input signals among the transmitters204included in the plurality of WDM modules104. SerDes Switch202may also be configured to switch from sending electrical signals to a failed transmitter204included in an active WDM module104to sending those electrical signals to a spare transmitter204included in a spare WDM module104. Accordingly, SerDes switch may be used to reroute traffic from a failed channel associated with a failed transmitter to a spare channel associated with a spare channel.

SerDes Switch202may be coupled to controller216. Controller216may include any system, apparatus or device configured to perform calculations or operations or direct other components within transponder102to perform operations. For example, controller216may direct and control SerDes Switch202to switch sending traffic from one transmitter204in a WDM module104to another transmitter204included in the same or a different WDM module104.

Controller216may include a processor and memory. The memory may store information, instructions or both and the processor may be configured to execute the instructions with respect to the stored information. Although only one controller216is depicted, transponder102may include one or more controllers216. Further, individual components within transponder102may included one or more controllers216also. For example, transponder102may include a traffic distribution circuit that includes SerDes Switch202and a controller216. The controller216included in the traffic distribution circuit may be configured to control the distribution of traffic by SerDes Switch202. Additionally, transponder102may include another controller216configured to control other components of transponder102.

Transmitters204included in WDM modules104may be communicatively coupled to SerDes Switch202. Each transmitter204may be any system, apparatus, or device configured to convert an electrical signal into an optical signal, and transmit the optical signal throughout an optical network. For example, transmitters204may each comprise a laser and a modulator configured to receive electrical input signals, and modulate the information contained in the electrical input signals onto the wavelength or channel of light produced by the laser, and transmit the wavelength of light with the information as an optical signal through a fiber.

Each transmitter204within a WDM module104may be associated with a specific and different wavelength band. Further, each transmitter204may be tuned to transmit an optical signal at a channel included in its respective wavelength band.

By being tunable to different channels within each wavelength band, each transmitter204within WDM modules104may transmit optical signals at various channels instead of having a specific transmitter to transmit optical signals at a specific channel. Further, by having a plurality of transmitters204that are configured to be tuned to transmit optical signals at channels within different wavelength bands, even more channels may be utilized without requiring a large number of different transmitters204.

Additionally, by having transmitters204being tunable over a limited wavelength band instead of the entire spectrum of wavelengths, each transmitter204may be less expensive, further reducing costs. However, the size of the wavelength bands may still require a much smaller number of different transmitters204necessary to transmit at the different channels within the system, which may reduce the necessity of manufacturing many different transmitters204. Thus, the costs associated with producing many different transmitters204may still be limited.

The number of different transmitters204in each WDM module104may be limited to the number of wavelength bands. Therefore, the number of different transmitters204necessary to include in one WDM module104may be limited, thus reducing costs. Alternatively a single type of tunable transmitter may be used that covers the entire spectrum but without the requirement of having to operate to specification outside of a designated wavelength band associated with the necessary spectrum. The illustrated embodiment utilizes four wavelength bands; thus, each WDM module104may include four different transmitters204with each transmitter204corresponding to a different wavelength band. However, other systems may include more or fewer transmitters204, depending on the requirements and limitations of the system, without departing from the scope of the present disclosure.

To further explain wavelength bands and the channels included within the wavelength bands, reference is now made toFIG. 3.FIG. 3illustrates a plurality of wavelength bands comprising a plurality of channels. In the present example, a wavelength spectrum300may be divided into four equal wavelength bands—band302A, band302B, band302C and band302D. Each band302may represent a range of wavelengths within spectrum300.

Each band302may also be further divided into a plurality of channels304. Each channel304may comprise or be associated with (e.g. centered around) a discrete wavelength within each band302. In the present example, each band302may include thirty discrete channels304. For example, band302A may include channels304A-1,304A-2,304A-3. . .304A-30. Accordingly, in the present example, if each channel within spectrum300were utilized for transmitting optical signals, one hundred twenty (120) different channels may be utilized (4 bands×30 channels/band=120 channels).

Although, in the present example, spectrum300is shown to include four bands302with each band including thirty channels304, the present disclosure should not be limited to such. The number of bands and channels may be more or fewer depending on the system requirements and capabilities. For example, the number of bands may depend on the number of channels implemented in a system and the tuning spectrum of transmitters204.

Returning toFIG. 2, each transmitter204in modules104may correspond with a wavelength band depicted inFIG. 3. For example, transmitter204A-1included in module104-1may correspond to band302A, transmitter204B-1may correspond to band302B, transmitter204C-1may correspond to band302C and transmitter204D-1may correspond to band302D. Transmitters204included in modules104-2through104-30may also similarly correspond to bands302A-302D.

Each transmitter204within modules104may also be tuned to specific channels that correspond with that module104. For example, module104-1may correspond with the first channel of each band302. Thus, transmitter204A-1may be tuned to channel304A-1of band302A, transmitter204B-1may be tuned to channel304B-1of band302B, transmitter204C-1may be tuned to channel304C-1and transmitter204D-1may be tuned to channel304D-1. The remaining modules104may similarly correspond to specific channels, and the transmitters204may similarly be tuned to these corresponding channels.

The number of modules104included in transponder102may correspond to the number of channels per band304because each module104may correspond with a specific channel304within bands302. In the present example, each band302may include thirty channels304; therefore transponder102may include thirty different modules104with four transmitters104each. Each transmitter104may transmit an optical signal at a different channel, thus giving the system the capability of transmitting optical signals at one hundred twenty (120) different channels.

Even though transponder102may transmit optical signals at one hundred twenty different channels, only one type of module104that includes only four different types of transmitters204may be necessary. Thus, modules104may be mass produced at a lower cost and may be interchanged at will to accommodate the full bandwidth of the system instead of relying on individual, channel specific components that may be expensive and difficult to replace to achieve the same bandwidth.

Modules104may also include multiplexers206optically coupled to transmitters204and configured to combine the optical signals transmitted by transmitters204into a single, multiplexed, optical signal. For example, multiplexer206-1may receive optical signals from transmitters204A-1,204B-1,204C-1and204D-1and combine these optical signals into a single optical signal. Multiplexers206may combine the optical signals using any suitable wavelength division multiplexing technique. Multiplexers206may comprise any system, apparatus or device configured to perform such operations.

Transponder102may also include a cyclic multiplexer210configured to receive the optical signals from modules104at input ports209. Each input port209may be configured to receive optical signals transmitted at a specific channel304within wavelength bands302. For example, input port209-1may be configured to receive optical signals transmitted at channels304A-1,304B-1,304C-1and304D-1.

Each band302may represent a different cycle of cyclic multiplexer210because input ports209of cyclic multiplexer210may only receive and combine optical signals transmitted at specific wavelengths or channels spaced apart by the wavelength range (width) of each band302. For example, channels304A-1and304B-1are spaced apart by the width of bands302. Thus, because input port209-1is configured to receive optical signals transmitted at channels304spaced apart by the width of bands302(e.g.,304A-1,304B-1,304C-1and304D-1) input port209-1may be configured to receive optical signals transmitted at a channel once every band or cycle, starting at channel304A-1. Input ports209-2through209-30may be similarly configured. Cyclic multiplexer210may comprise any system, apparatus, or device configured to receive and combine optical signals according to cycles.

Accordingly, the optical signals from each module104may be sent to the input port209that corresponds with the channels of that module104. For example, transmitters204A-1,204B-1,204C-1and204D-1included in module104-1may respectively transmit optical signals at channels304A-1,304B-1,304C-1, and304D-1. Thus, the optical signals leaving module104-1may comprise optical signals transmitted at each of these channels. As stated above, port209-1may be configured to receive optical signals transmitted at channels304A-1,304B-1,304C-1, and304D-1. Therefore, module104-1may be associated with input port209-1such that optical signals from module104-1are sent to input port209-1. Modules104-2through104-30may similarly be associated with input ports209-2through209-30.

Cyclic multiplexer210may be configured to combine the optical signals received at input ports209into a single optical output signal to be transmitted via output port106. In the present embodiment, the optical signal leaving cyclic multiplexer210may comprise as many as one hundred twenty channels. The optical signal received at each input port209may comprise four channels that correspond to the four channels of transmitters204included in modules104. Cyclic multiplexer210may include thirty input ports209to correspond with the thirty modules104that may be included in transponder102. Accordingly, a single optical output signal of cyclic multiplexer210may comprise one hundred and twenty channels. If each channel may transmit optical signals at ten gigabits per second, cyclic multiplexer210may output an optical signal with a bandwidth capability of 1.2 terabits per second.

Thus, by interfacing SerDes Switch202, modules104and cyclic multiplexer210, transponder102may transmit a high bandwidth optical signal using low cost, interchangeable components, instead of the high cost, specialized components used in other systems. The transmission system can be made tolerant to WDM module failures, which can be corrected in-service. Multiple levels of multiplexing and pluggable submodules may be used.

The transponder on the receiving end may contain a single multi-wavelength receiver connected to a SerDes Switch, or a similar structure of multiple stages of demultiplexing and multi-wavelength receiver units connected to the SerDes Switch. The receivers may be separate or included in WDM modules. The SerDes switch may ensure proper ordering of signals and combining of these into an appropriately formatted digital signal stream to be outputted over the electrical interface.

FIG. 4illustrates an example method400for interfacing a plurality of WDM modules to achieve a high bandwidth optical signal at a low cost.

Method400may start at step402, and transponder102may tune each transmitter204in WDM modules104to the channels304associated with each module104. At step404, each transmitter204of each WDM module104may transmit optical signals at its tuned channel304within its associated band302.

At step406, each module104may combine the optical signals transmitted by the transmitters204into a single, multiplexed, optical signal. Each module104may also send the optical signals to an input port209of cyclic multiplexer210optically coupled to the module104. The input port209may be configured to receive optical signals transmitted at the channels associated with the module104.

At step408, cyclic multiplexer210may combine the optical signals received at input ports209into a single optical signal. At step410, cyclic multiplexer210may send the single optical signal through optical output port106and method400may end.

Modifications, additions or omissions may be made to method400without departing from the scope of the disclosure.

Returning toFIG. 2, transponder102may also include other components to facilitate detecting a failure of one or more transmitters204. Transponder102may also include components to facilitate determining if a transmitter204has drifted from transmitting at its desired channel304. Further, these additional components may facilitate in interfacing a new module104with transponder102.

Transponder102may be configured to determine if one or more transmitters204have failed, thus requiring replacement of a module104. Transponder102may include a power monitor208, optically coupled to the output of each multiplexer206. Power monitors208may comprise any system, apparatus or device configured to detect, or measure, or detect and measure the power of the optical signals leaving multiplexers206. In some embodiments power monitors208may comprise a photodiode or any other suitable device that detects the amount of power leaving multiplexers206. In other embodiments power monitors208may comprise a photodiode coupled to a controller configured to measure the power detected by the photodiode and perform operations with respect to the power detected.

Transponder102may include a power monitor208for each module104, such as that depicted with respect toFIG. 2. In other embodiments, transponder102may include a power monitor208configured to monitor the power of more than one module104. In such embodiments, transponder102may also include a switch (not depicted inFIG. 2) coupled to the power monitor208and the output of the plurality of modules104. The switch may include a plurality of input ports and may be configured to receive a portion of the output signals from the modules104at its input ports. The switch may also include an output port coupled to the power monitor208. The output port may be configured to output one of the signals received at one of the input ports. The switch may also be configured to cycle through each of its input ports such that the output port sequentially outputs each signal received at each of the input ports over a given period of time.

Therefore, due to the signal received at each input port of the switch being associated with the output of each module104, the output of the switch may sequentially output a portion of each signal associated with each module104. Accordingly, the power monitor208coupled to the output of the switch may monitor the power of a plurality of modules104.

In some embodiments, power monitors208may detect a failure of a transmitter204. For example, power monitor208-1may measure the power of the optical signal from multiplexer206-1. If all transmitters204-1are functioning, the amount of power detected by power monitor208-1may be at a certain level. However, if one or more transmitters204-1fail, the amount of power detected by power monitor208-1may decrease substantially due to an optical signal being lost. Accordingly, power monitor208-1may detect that one or more TX's204-1have failed and that the channels associated with the failed transmitters are subsequently unavailable for carrying traffic.

In another embodiment, transponder102may determine that a transmitter204has failed by comparing the power level measured by a power monitor208with a target power level. A desired or target power level may be set for the optical signals leaving modules104. A system administrator may set the target power level, or upon initialization of a module104after all configurations are completed, the power level of the optical signal leaving the module104may be measured and set as the target power level.

Power monitor208may be coupled to controller216. Although only one controller216is depicted, in other embodiments, each power monitor208may include a controller216that directs and performs the operations with respect to that particular power monitor208.

Controller216may be configured to measure the power detected by power monitor208and compare that measured power with the target power level. If the measured power is substantially equal to the target power, controller216may determine that none of the transmitters204included in the module104have failed. However, if the measured power is substantially less than the target power, controller216may determine that one or more transmitters204have failed. The controller may execute additional tests to assess the situation in more detail.

After determining that a transmitter204within a module104has failed, controller216may direct that an indicator112, as depicted inFIG. 1, indicates that the module104includes a failed transmitter204.

FIG. 5illustrates an example method500for determining if a transmitter204within a module104has failed.

Method500may start, and, at step502, controller216may measure the power output of a module104, using a power monitor208or any other suitable device.

At step504, controller216may save the measured power as a target power output for the optical signal leaving the module104. In alternative embodiments, a system administrator may enter a power level for the target power output level and controller216may save the entered power level as the target power output level.

At step506, controller216may continue measuring the power level of the optical output signal of the WDM module104. At step508, controller216may compare the measured power with the saved target power.

At step510, controller216may determine if the measured power is less (or more) than the target power according to a deviation threshold. If the measured power is not less than the target power according to the deviation threshold, method500may return to step506. If the measured power is less than the target power according to the deviation threshold, method500may proceed to step512.

Deviation thresholds may be selected to avoid false failure alarms due to typical power variation due to environmental conditions, acceptable degradations over time and appropriately detect critical loss of performance. For example, the threshold may be set to correspond to a specified maximum reduction of transmitter output power of 10%. In a WDM module that includes four transmitters and assuming that the output power from the other transmitters does not increase, the deviation threshold may be set to 2.5% (10%/4).

Alternatively, if the link can tolerate larger deviations, the deviation threshold may be set to correspond to a maximum allowed deviation per transmitters. For instance, if a 50% change per channel is tolerated, and assuming the output power of individual transmitters might rise by up to 10%, and if there are four transmitters in a module, the deviation threshold may be set to 1*(¼)*50%−3*(¼)*10%=5%.

In another example, if laser output power can only decrease, the deviation threshold may be set to 1*(¼)*50%=12.5% to decrease the number of times it is determined that a WDM module potentially includes a failed transmitter. Finally, to allow larger acceptable variations of output power variations of transmitters due to expected drift, the system may re-calibrate the output power of the transmitters periodically or after a determination that a transmitter has failed. Thus, a suitable deviation threshold may be selected depending on the specific design and device characteristics of the system to ensure reliable operation of the system.

At step512, controller216may determine that a transmitter204within module104has failed due to the reduced power. At step514, controller216may indicate that the WDM module104includes a failed transmitter and method500may end.

Modifications, additions or omissions may be made to the steps in method500without departing from the scope of the disclosure. For example, the target power may be measured upon initialization of a module104, or it may be set by a system administrator. Also, although method500has been described with respect to controller216performing the steps, any appropriate component included within transponder102may perform, one or more of the steps described without departing from the scope of the disclosure.

Transponder102may also be configured to determine or detect if one or more transmitters204are transmitting optical signals at channels304other than their desired channels304.

Cyclic multiplexer210may be configured to divert optical signals transmitted at channels that input ports209are not configured to receive but that are sent to input ports209anyway. Cyclic multiplexer210may divert these offset signals to an offset output212instead of combining them with the other optical signals. Cyclic multiplexer210may include one or more offset outputs212.

In the present embodiment, cyclic multiplexer210includes offset output212A and offset output212B. Cyclic multiplexer210may be configured to send optical signals transmitted at channels below the target channels to offset output212A and may be configured to send optical signals transmitted at channels above the target channel to offset output212B. By diverting optical signals—transmitted at channels that an input port209is not configured to receive—to offset outputs212, cyclic multiplexer210may indicate that a transmitter204is transmitting at a channel that is different than its desired channel304.

Offset outputs212may each be coupled to an offset monitor214. Offset monitors214may indicate if an optical signal is diverted to offset outputs212by detecting optical signals transmitted from offset outputs212. Offset monitors214may also measure the power of optical signals transmitted out of offset outputs212and thus, determine, or be used to determine, if a transmitter204is transmitting optical signals at a channel that is different than its desired channel.

For example, transmitter204A-2may be transmitting optical signals at channel304A-1instead of channel304A-2, and, therefore, optical signals sent to input port209-2may include optical signals sent at channel304A-1. Because input port209-2may not be configured to receive optical signals sent at channel304A-1, and because channel304A-1is below the target channel of304A-2, cyclic multiplexer210may divert the optical signals transmitted at channel304A-1to offset output212A. Alternatively if transmitter204A-2were transmitting optical signals at channel304A-3instead of the target channel of304A-2, cyclic multiplexer210may divert the optical signals transmitted by transmitter204A-2at channel304A-3to offset output212B.

In addition to determining that a transmitter204within a module104has failed, Controller216may also determine which transmitter204has failed by utilizing offset output monitors214.

FIG. 6illustrates an example method600for identifying a failed transmitter. Method600may start, and at step602, using a method similar to method500disclosed inFIG. 5, controller216may determine that a transmitter204within a module104has failed. In the present example, controller216may determine that a transmitter204within module104-2has failed.

At step604, controller216may tune each transmitter204within the module104, to a channel304adjacent to the target channel of that transmitter204. For example, controller216may tune transmitter204A-2to channel304A-1instead of the target channel of304A-2for transmitter204A-2.

At step606, controller216may determine if an offset monitor214is detecting an optical signal or measuring the power of an optical signal due to the transmitter204being tuned to an offset channel. In the present example, controller216may determine if offset monitor214A is detecting the optical signal from transmitter204A-2, due to transmitter204A-2being tuned to channel304A-1instead of304A-2. If offset monitor214detects an optical signal, method600may proceed to step608, otherwise method600may proceed to step610.

At step608, controller216may determine that the transmitter204has not failed if offset monitor214detects an optical signal, because power detected by offset monitor214indicates that the transmitter204is still transmitting an optical signal. In the present example, if offset monitor214A detects an optical signal, controller216may determine that transmitter204A-2has not failed.

At step609, controller216may tune the transmitter204back to its target channel and tune another transmitter204to its adjacent channel at step604to determine if the other transmitter204is the failed transmitter204. In the present example, controller216may tune transmitter204A-2to its target channel of304A-2at step609and tune transmitter204B-2to channel304B-1—a channel adjacent to its target channel of304B-2—at step604, to determine if transmitter204B-2has failed.

At step610, controller216may determine that the transmitter204has failed if offset monitor214does not detect an optical signal. In the present example, if the transmitter204A-2were working properly, offset monitor214A should detect the optical signal from transmitter204A-2due to transmitter204A-2being tuned to offset channel304A-1. Therefore, if transmitter204A-2is tuned to an offset channel304A-1and offset monitor214A does not detect an optical signal, controller216may determine that transmitter204A-2has failed.

At step612, controller216may direct SerDes Switch202to route electrical signals from the failed transmitter204to a spare transmitter204, such that traffic may be routed from the channel associated with the failed transmitter to the spare channel associated with the spare transmitter. In the present example, transmitter204A-30may comprise a spare transmitter204and if controller216determines that transmitter204A-2has failed, controller216may direct SerDes Switch202to direct electrical signals from transmitter204A-2to transmitter204A-30. Alternatively, before tuning a channel, traffic may be temporarily redirected to a spare channel to perform parts of procedure600without degrading service and the redirection may be undone after step609.

At step614, controller216may determine if all the transmitters204within the module104have been checked. If all the transmitters204have been checked, method600may end, otherwise, method600may return to step604and check another transmitter204.

Modifications, additions, and omissions may be made to method600without departing from the scope of the disclosure. For example, transponder102may not include any spare modules or spare transmitters, and thus, step612may not be necessary. Also, while determining which transmitters have failed in a particular module104, controller216may direct all of the electrical signals away from the transmitters in that module to the transmitters in a spare module to ensure that no information is lost while tuning transmitters to offset channels.

Additionally, in an alternative embodiment, controller216may tune each transmitter204to a wavelength somewhere between the adjacent channel and the target channel such that the offset monitor may still detect the optical signal, but also such that enough of the optical signal from the transmitter204is sent to output106. Therefore, information carried at the channel of the transmitter204being tuned may still be transmitted while simultaneously determining which transmitter204may have failed. As described with respect toFIG. 7, this tuning may also be used to continuously check the wavelength of each laser and for re-tuning any lasers to a target wavelength, to eliminate wavelength locking or laser wavelength stabilizing function associated with the lasers within the WDM modules which may further reduce cost.

Also, although method600has been described with respect to controller216performing the steps, any appropriate component included within transponder102may perform, one or more of the steps described without departing from the scope of the disclosure.

Controller216may also be configured to determine that a transmitter204within a module104has drifted from its desired wavelength by utilizing offset monitors214.

FIG. 7illustrates an example method700for detecting wavelength drift of a transmitter204. Method700may start, and, at step702, offset monitors214may measure power at offset outputs212.

At step704, controller216may determine if an optical signal is detected or measured by offset monitors214. If offset monitors214do not detect any optical signals or measure any power at offset outputs212, method700may return to step702. If controller216determines that either offset monitor214or both offset monitors214detect optical signals, method700may proceed to step706.

At step706, controller216may determine that a transmitter204has drifted from its desired channel or wavelength because one or more offset monitors214are detecting optical signals and measuring power at one or more offset outputs212.

At step708, controller216may locate the transmitter204that has drifted from its target wavelength. Controller216may identify which transmitters experience wavelength drift in step708ofFIG. 7by utilizing offset monitors214as described inFIG. 8.

At step710, controller216may determine if the transmitter may be retuned to its targeted channel or wavelength. If the transmitter has merely drifted away from its original tuning and may be retuned, method700may proceed to step712. If the transmitter has drifted due to a failure such as a tuner failure, method700may proceed to step714.

At step712, controller216may retune the transmitter to its desired channel and method700may end.

At step714, controller216may indicate that the module104includes a failed transmitter. At step716, controller216may direct SerDes Switch202to route electrical signals from the failed transmitter to a spare transmitter, such that traffic is rerouted from the failed channel to a spare channel, and method700may end.

Modifications, additions, or omissions may be made to method700without departing from the scope of the disclosure. For example, transponder102may not include any spare modules or spare transmitters, and thus, step716may not be necessary. Additionally, although method700describes locating a transmitter204with wavelength drift, the present disclosure should not be limited to determining a single transmitter with wavelength drift. Further, although the method has been described with respect to controller216performing the steps, any suitable component of transponder102may perform some or all of the steps described.

FIG. 8illustrates an example method800for locating a transmitter with a drifted wavelength.

Method800starts, and, at step802, controller216may determine that a transmitter has drifted from its desired wavelength. Controller216may determine this using method700described inFIG. 7, or any other suitable method.

At step804, controller216may modulate a different tone onto each optical signal transmitted by each transmitter204within transponder102. A tone may comprise a unique, low-frequency intensity modulation that is imposed on the wavelength of the channel and easily detectable.

At step806, controller216may detect a tone within the offset signal detected by the offset monitor214. At step808, controller216may compare the detected tone with one of the other modulated tones associated with each transmitter204.

At step810, controller216may determine if the detected tone equals the compared tone. If the detected tone does not equal the compared tone, controller216may return to step808and compare the detected tone with another tone. However, if the detected tone does equal the compared tone, controller216may proceed to step812.

At step812, controller216may determine which transmitter204is associated with the detected tone. At step814, controller216may determine that the transmitter204associated with the detected tone has wavelength drift and method800may end. Thus, controller216may locate which transmitter has drifted from its desired wavelength.

Modifications, additions, or omissions may be made to method800without departing from the scope of the disclosure. For example, in alternative embodiments, controller216may modulate a single tone onto each optical signal transmitted by each transmitter, one at a time, instead of modulating a different tone onto each channel at the same time. Thus when the tone is detected on the offset signal, controller216may know which transmitter is associated with the offset signal.

Also, although method800has been described with respect to controller216performing the steps, any appropriate component included within transponder102may perform, one or more of the steps described without departing from the scope of the disclosure.

Controller216, power monitors208and offset monitors214may also facilitate interfacing a new module104with a transponder102. A new module104may be interfaced with a transponder102upon replacement of a defective module104, or initialization of a transponder102.

Method900may start, and, at step902, a module104may be inserted into transponder102. Once a new module104is inserted into a slot included in transponder102, the power of the optical output signal may need to be set to a desired level. The power level of each individual optical signal transmitted by each transmitter204may need to be set and measured individually to create the desired power level of the optical output signal of the entire module104. If the power level of the optical output signal as a whole of the new module104were set, the power of one transmitter204may be much higher than another transmitter204, but the power level of the module104as a whole may still be at the desired power level.

To ensure that each transmitter204is transmitting at a desired power level, controller216may use offset monitor214A or214B.

At step902controller216may tune a transmitter204of the new module104to the channel adjacent to the desired channel of that transmitter204, thus creating an optical output signal at one of the offset outputs212to be detected or measured by one of the offset monitors214.

At step904, controller216may measure the power of the optical signal received at the offset output212using the offset monitor214that corresponds with the offset output212. In alternative embodiments, offset monitor214may include its own controller that measures the power of the optical signal detected by offset monitor214, and that controller may convey that information to controller216.

At step908, controller216may determine if the measured power from the offset output212equals a desired power, or is in a range of acceptable power, for that transmitter. A system administrator may determine the desired power for each transmitter204. If the measured power equals the desired power, or is in a range of acceptable power, method900may proceed to step910. If the measured power does not equal the desired power, or is not within the range of acceptable power, method900may proceed to step914.

At step910, with the transmitter power adjusted to the desired power level, controller216may tune the transmitter204from the adjacent channel to the target channel.

At step912, controller216may determine if all of the transmitters204in the new module have been adjusted to their desired power level. If all the transmitters204have been adjusted, method900may end. Otherwise, method900may return to step904and controller216may tune another transmitter to the channel adjacent to the desired or target channel until the power of all transmitters has been adjusted.

At step914, if, at step908, the measured power does not equal the desired power for that transmitter204, controller216may adjust the power of the transmitter204. After step914, controller216may return to step906to measure the power again. Controller216may repeat steps908,914and906until the power measured by the offset monitor214equals the desired power level for that transmitter204. After adjustment of all transmitter power levels of a WDM module, the total output power at the output of the module may be recorded as a reference to detect output power degradation or failure.

The system may perform regular re-calibration of output power during which traffic may be temporarily redirected to a spare channel.

Modifications, additions, and omissions may be made to method900without departing from the scope of the disclosure. For example, by utilizing more than one offset monitor at a time, controller216may adjust the power of more than one transmitter204at a time.

As mentioned previously, modules104may comprise active modules104and spare modules104and when a transmitter204within an active module104fails, transponder102may direct traffic from the failed channel to a spare channel by sending electrical signals away from the failed active transmitter204to a spare transmitter204included in the spare module104. The term “active” may refer to any module104, transmitter204or channel designated to be currently transmitting or carrying optical signals. The term “spare” may refer to any module104, transmitter204, or channel configured to transmit or carry traffic that may have initially been associated with an active module104, transmitter204, or channel.

FIG. 10illustrates an example implementation and utilization of active and spare modules104within a transponder102.

Transponder102may include modules104-1,104-2,104-3and104-4. Transponder102may also include an empty slot103. Modules104may each include four transmitters204as depicted inFIG. 2. However, in alternative embodiments, modules104may include more or fewer than four transmitters. Although four modules104are depicted, transponder102may include more or fewer modules104than those depicted. For example, transponder102may include thirty modules104as depicted inFIGS. 1 and 2. Additionally, transponder102may include more than the one empty slot103depicted. The number of modules104and spare slots103depicted is merely for illustrative purposes.

At time T1, modules104-1-104-3may comprise active modules and transponder102may send electrical signals1001to transmitters204included in modules104-1-104-3accordingly. For example, transponder102may respectively send electrical signals1001A,1001B,1001C and1001D to the four transmitters204(not expressly shown) included in module104-1; transponder102may respectively send electrical signals1001E,1001F,1001G and1001H to the four transmitters204(not expressly shown) included in module104-2; etc. Additionally, module104-4may comprise a spare module, thus, transponder102may initially send no electrical signals to the transmitters204included in module104-4, such that the transmitters included in module104-4are spare transmitters on standby.

In order for spare transmitters204to be on standby, the channels associated with those transmitters204may not be utilized during normal operation of transponder102, or utilized for a different non-critical purpose. Those channels may be reserved for transmission of optical signals associated with the redirection of electrical signals to spare transmitters. Accordingly, the bandwidth capabilities of transponder102may be higher than the bandwidth requirements of the system in which transponder102is implemented.

At time T2, transmitter204A-1receiving electrical signals1001A may fail, causing the failure of the channel associated with the failed transmitter also. Transponder102may detect this failure and reroute traffic from the failed transmitter to a spare transmitter by rerouting electrical signals1001A from failed transmitter204A-1in active module104-1to spare transmitter204A-4included in spare module104-4. Accordingly, transponder102may continue transmitting optical signals without losing bandwidth.

Additionally, the use of empty slot103allows for delayed replacement of module104-1. By allowing for a second spare module, (e.g., leaving a slot empty), immediate replacement of module104-1may not be required to prevent a later loss of bandwidth.

For example, if transmitter204A-2receiving electrical signals1001E were to fail, electrical signals1001E may be rerouted to another spare transmitter204included in spare module104-4. Accordingly, only two of the four spare transmitters in spare module104-4may be available for receiving electrical signals, thus leaving only two spare channels available. In the present example, by utilizing a spare slot103, either module104-1or104-2may be replaced without losing bandwidth. Another WDM module104may be inserted into spare slot103. Upon removing either module104-1or104-2to replace the defective module, the traffic carried by the channels associated with the three remaining active transmitters in the removed module may be directed to the channels associated with the replacement module and the system may maintain its bandwidth. Without spare slot103available to receive the replacement module, spare module104-4may only have two spare transmitters (and consequently two spare channels) available for receiving the traffic directed from the three channels associated with the previously active transmitters of the removed module, thus causing a loss in bandwidth. Accordingly, spare slot103allows for delayed replacement of a module with a defective transmitter.

At time T3, before module104-1has been replaced, transmitter204A-2receiving electrical signals1001E may fail, transmitter204B-3receiving electrical signals1001J may fail, and transmitter204C-3receiving electrical signals1001K may also fail. Based on these failures, transponder102may respectively route electrical signals1001E,1001J and1001K to spare transmitters204B-4,204C-4and204D-4included in spare module104-4. Accordingly, transponder102may switch traffic from the failed channels associated with the failed transmitters to the spare channels.

Spare module104-4may now have electrical signals1001A,1001E,1001J and1001K routed to each of its transmitters204such that no more electrical signals1001from other active transmitters204may be routed to spare module104-4. At this point, one or more of the modules104with failed transmitters204should be replaced because if another transmitter204fails, no more spare transmitters204are available to receive electrical signals and transmit traffic over spare channels associated with spare transmitters204. Accordingly, if another transmitter204fails, transponder102's bandwidth may drop below the system requirements, which may cause slower communication, lost information or both.

Additionally, in some embodiments, transponder102may be configured to determine an order of replacement of modules104based on various factors such as the number of failed transmitters within a module104and the fitness of a module104. Transponder102may determine the fitness of a module104based on operating hours of the module104, the temperature of the module104and the number of failed transmitters of the module104. In other embodiments, transponder102may also be configured to calculate a recommended time of next service of the transponder based on the total number failed channels before the number of failed channels requires immediate replacement of a module to prevent a loss of bandwidth and traffic. Transponder102and/or modules104may comprise one or more indicators that indicate the order of removal of one or more modules104, the fitness of one or more modules104and the recommended time of next service. Accordingly, transponder102may calculate and provide information for planning of service which may reduce the number of unexpected problems the may require expensive, immediate attention.

Transponder102may also include a mechanical locking mechanism (e.g. an electro-magnetic latch) that prevents removal of a module104at an inappropriate time to ensure that the module104being removed is the module104that transponder102has prepared for removal. Accordingly, the locking mechanism may prevent an interruption of service due to the improper removal of a module104.

At time T4, a system technician may insert a replacement module104—module104-5—into spare slot103. Replacement module104-5may replace one of modules104-1,104-2or104-3because each of those modules includes a failed transmitter. Module104-3may be replaced first because it has two failed transmitters204, instead of one like in modules104-1and104-2. Although module104-3may be replaced first because it has the most failed transmitters204, module104-3does not necessarily need to be replaced first. At time T4, transponder102may switch from routing traffic over the channels associated with module104-3to routing traffic over the channels associated with new module104-5.

For example, transponder102may route all the electrical signals1001that were originally sent to module104-3to new module104-5. For example, transponder102may route electrical signals1001I and1001L from transmitters204A-3and204D-3, included in active module104-3, to transmitters204A-5and204D-5included in new module104-5, and transponder102may route electrical signals1001J and1001K from transmitters204C-4and204D-4, included in spare module104-4, to transmitters204B-5and204C-5included in new module104-5.

Accordingly, spare transmitters204C-4and204D-4, and their respective channels, included in spare module104-4may be available again for transmitting and carrying traffic if another active transmitter204fails. Additionally, module104-3may be disabled to allow removal of module104-3without disrupting any traffic.

At time T5, module104-3may be removed to leave a spare slot103that may be used to receive another replacement module104. Modules104-1and104-2may also be replaced later using the same method. Alternatively, because spare module104-4has two spare transmitters204available, modules104-1and104-2do not need to be replaced, but may be replaced, if so desired. However, replacing all of the modules at one time may reduce maintenance costs because only one maintenance session is required to replace all three modules instead of having another visit to replace the modules with failed transmitters at a different time. Therefore, by utilizing spare module104-4and maintaining an empty slot103, the frequency of maintenance visits may be reduced, which also may reduce costs.

Modifications may be made to the implementation of spare modules104described inFIG. 10without departing from the scope of the disclosure. For example, electrical signals1001do not need to be routed to the particular transmitters204described. Electrical signals1001may be routed to any of the available spare transmitters204included in a spare module104without departing from the scope of the invention. Additionally, a transponder102may include more or fewer slots103and modules104. Also, each module104may include more or fewer transmitters204. The empty slot103may be populated with a WDM module on standby and provide one additional standby channel while allowing in-service repairs, without departing from the scope of the disclosure. Finally, more than one module104may be utilized as a spare module104depending on the system requirements and capabilities.

Method1100may start, and at step1102, transponder102may determine if a transmitter of one of the modules104has failed. If a transmitter has not failed, transponder102may continue monitoring for failed transmitters at step1102. But, if a transmitter has failed, method1100may proceed to step1104.

At step1104, transponder102may determine if a channel is available for carrying traffic. In some instances, transponder102may determine if a spare transmitter included in a spare module is available for receiving electrical signals originally routed to the failed transmitter. If a spare transmitter is available, at step1106, transponder102may reroute traffic from the failed channel to a spare channel. Transponder102may reroute traffic by routing the electrical signals sent to the failed transmitter from the failed transmitter to the available spare transmitter included in the spare module and method1100may return to step1102where transponder102may monitor for more failed transmitters.

If, at step1104, transponder102determines that no spare channels (e.g., spare transmitters) are available, transponder102may indicate, at step1108, that a replacement module is required. Transponder102may send a signal that alerts a network administrator, or perform any other suitable operation that may notify an administrator that no more spare transmitters are available and that the transmission bandwidth is not protected from failures.

If the policy is to ensure protection at all time, and the transponder102determines at step1104that there are 2 or less spare transmitters available, transponder102may direct electrical signals from a failed transmitter102to a spare transmitter102, and at the same time indicate that module replacement is required.

At step1110, transponder102may indicate which modules104include failed transmitters. In some embodiments, transponder102may send a signal that activates indicator112. Indicator112may generally indicate that a module includes failed transmitters, indicator112may more specifically indicate the number of failed transmitters in a module, indicator112may indicate which transmitters included in a module has failed, or any combination thereof. Accordingly, maintenance personnel may determine which modules104should be replaced and also may determine which modules104may have a higher priority for replacement. In addition, the system may provide guidance to the operator in which order to replace failed modules. At step1112the modules with failed transmitters may be replaced and method1100may end.

FIG. 12illustrates an example method1200for replacing modules with failed transmitters that may be performed in accordance with step1112of method1100.

Method1200may start, and, at step1202, a replacement module may be inserted into a spare slot of transponder102. At step1204, transponder102may route all the electrical signals originally associated with the failed transmitters, of the module to be replaced, from the spare transmitters presently receiving the electrical signals to the replacement module (e.g., transponder102routing electrical signals1001J and1001K from spare module104-4to replacement module104-5at time T4inFIG. 10).

At step1206, transponder102may route all the traffic sent to the still active transmitters of the module to be replaced to the replacement module (e.g., transponder102may route electrical signals1001I and1001L from active module104-3to replacement module104-5at time T4inFIG. 10). Although steps1204and1206have been described as two discrete steps, as shown inFIG. 10, transponder102may also perform the steps simultaneously.

At step1208, the defective module may be removed. At step1210, transponder102may determine if all the defective modules have been replaced. If all of the defective modules have been replaced, method1200may proceed to step1212.

If all of the defective modules have not been replaced, method1200may return to step1202to replace another defective module.

At step1212, the slot previously occupied by the now removed defective module may be left empty until another module may need to be replaced. Alternatively the empty slot may be populated with an additional spare WDM module, as discussed in further detail with respect toFIG. 13. Following step1212, method1200may end.

Additions, modifications or omissions may be made to method1200without departing from the scope of the disclosure. For example, although method1200describes repeating method1200until all defective modules have been replaced, method1200may be utilized to replace fewer than the number of defective modules. Additionally, method1200may be used to replace a module that has not been deemed defective, but may be replaced for some other reason.

At time T1, transponder102may include active modules104-1,104-2, and104-3. At time T1, transponder102may transmit traffic over active channels associated with active transmitters included in active modules104-1,104-2, and104-3. For example, transponder102may direct electrical signals1301, similar to electrical signals1001inFIG. 10to transmitters (not expressly shown) included in active modules104-1,104-2, and104-3such as described with respect toFIG. 10. Transponder102may also include spare module104-4, like spare module104-4inFIG. 10, however, unlike inFIG. 10, transponder102may also include spare module104-5instead of merely maintaining an empty slot103, which may make more spare channels available.

At time T2, the transmitters receiving electrical signals1301A,1301E,1301H,1301J and1301L may have all failed, causing their respective channels to fail. Transponder102may switch from the failed channels to spare channels by redirecting these electrical signals1301to spare transmitters included in spare modules104-4and104-5. Transponder102may also direct that active modules104-1,104-2and104-3indicate that they include one or more defective transmitters, and thus need to be replaced.

With all the spare transmitters being utilized in spare module104-4and only three spare transmitters remaining in spare module104-5, at least one of the active modules104with a defective transmitter may need to be replaced before another transmitter fails, if transponder102is to maintain the required bandwidth of the system upon replacement of any module with failed transmitters. For example, the transmitter receiving electrical signals13011may also fail, thus transponder102may redirect electrical signals13011to a spare transmitter in spare module104-5, and thus may utilize another spare channel. However, now only two spare channels (e.g., transmitters) may be available. Replacing module104-1may not be accomplished without losing information or bandwidth, because electrical signals sent to three transmitters204included in module104-1(e.g., electrical signals1301B,1301C, and1301D) need to be redirected before removing module104-1. Accordingly, a module104may be replaced before such a scenario occurs.

To avoid the scenario just described, at time T3, transponder102may prepare to have module104-1replaced. Transponder102may route traffic from the channels associated with module104-1to spare channels. For example, the electrical signals1301routed to the active, operating transmitters in module104-1may be routed to the available spare transmitters of spare module104-5(e.g., transponder102may route electrical signals1301B-1301D to transmitters included in module104-5). After the traffic has been rerouted to spare channels, (e.g., electrical signals have been rerouted), module104-1may be disabled.

At time T4, module104-1may be replaced by replacement module104-6. Transponder102may route electrical signals1301A-1301D to the transmitters included in replacement module104-6. Accordingly, spare module104-4may have an available spare transmitter that was previously receiving electrical signals1301A, and the transmitters included in spare module104-5that were receiving electrical signals1301B-1301D may also be available. Consequently, the spare channels associated with spare module104-5may be available to carry traffic. Modules104-2and104-3may also be replaced in a similar manner such that transponder102does not include any defective modules.

Although in the present example only one transmitter may be utilized in module104-5before replacement of a module, having two spare modules populating slots in transponder102instead of one spare transmitter and one empty slot allows for more transmitters to fail before replacement of modules is necessary. In contrast toFIG. 10, in the present example ofFIG. 13, five transmitters may fail instead of four. By populating a spare slot103, an additional transmitter may fail before needing to replace a defective module. The startup cost of populating the spare slot may be a little higher because one more modules may need to be used upon implementation. However, overall costs may be reduced—allowing for extra transmitters to fail before necessitating a maintenance visit may reduce the number of maintenance visits and costs.

In an alternative example, transponder102may be configured to determine the number of failed transmitters per module. If a module has more than one failed transmitter, and transponder102can determine this, more spare transmitters may have electrical signals1301routed to them before replacement of modules is required.

For example, at time T2, transponder102may determine that another active transmitter may fail before replacement of a module is necessary if the module that needs to be replaced is not module104-1. Modules104-2and104-3each have two failed transmitters, and therefore each have only two active, operational transmitters receiving electrical signals1301and transmitting traffic over channels associated with the two operational transmitters. Accordingly, only two available spare transmitters may be required to remove and replace modules104-2and104-3. Therefore, at time T2, even if another transmitter failed (e.g., the spare transmitter receiving electrical signals1301A at time T2), requiring rerouting of traffic to another spare channel (e.g., electrical signals1301A routed from the failed transmitter in module104-4to a spare transmitter in104-5), a sufficient number of spare transmitters may remain available to still replace modules104-2and104-3.

When an empty spare slot is populated with a spare WDM module that may provide additional spare channels, transponder102may determine whether a spare transmitter is available in a spare module or not by determining which active WDM module or modules include the largest number of failed channels. Transponder102may compare the number of active operational transmitters in the WDM module or modules with the most failed transmitters with the number of un-used spare channels. If the number of un-used spare channels is less than or equal to the number of active, operational channels in the WDM module with the largest number of failed transmitters, transponder102may determine that a sufficient number of spare channels are not available.

In case an empty spare slot is populated and if the policy is to ensure protection at all times, transponder102may direct traffic from a failed transmitter to a spare, and at the same time indicate that module replacement is required if the number of un-used spare channels is one more than the number of un-used spare channels or less.

However, in such a scenario, the module or modules with the largest number of failed transmitters may need to be replaced first to prevent bandwidth loss. Accordingly, transponder102and the modules104may also require functionality to indicate which modules should be replaced first, allowing maintenance personnel to replace the modules in the proper order. In some embodiments, transponder102may direct indicator112to indicate the replacement priority of a module, which module or modules include the most failed transmitters, which individual transmitters have failed in each module or any combination thereof. Depending on the technology used for the tunable transmitters, one failed transmitter may be the result of worse than average reliability of all the transmitters in the WDM module, making failure of multiple transmitters in the same module more likely. Thus, potentially, even a larger number of transmitters may fail before requiring replacement of a module, further reducing the costs associated with maintenance visits.

Modification, additions, or omissions may be made to the implementation of spare modules as described inFIG. 13. For example, more spare modules104may be utilized and transponder102may also include more or fewer active modules104. Additionally, although module104-1was described as being the first module to be replaced, modules104may be replaced in any order without departing from the scope of the disclosure.

Also, transponder102inFIG. 13may be configured to determine a fitness of modules104, replacement order of modules104and a next time of service of transponder102similar to that described with respect toFIG. 10. Additionally, transponder102may include a mechanical locking mechanism similar to that described with respect toFIG. 10.

In yet other embodiments, a traffic distribution circuit comprising a controller and SerDes switch may be configured to duplicate traffic and send one copy to a spare channel. In other embodiments, the traffic distribution circuit may be configured such that traffic carried by a failed channel is transmitted in any other way using spare channels to maintain a particular guaranteed transmission capacity.

For example, the traffic distribution circuit could use four wavelengths from spare module104-4and one wavelength from spare module104-5partially, to transmit traffic corresponding to one failed channel across all five physical spare channels. Accordingly, the spare channels may comprise virtual or logical spare channels instead of physical spare channels.

FIG. 14illustrates an example method1400for utilizing two spare modules that are populating two spare slots in a transponder102. Method1400may start, and, at step1402, transponder102may determine if a transmitter included in a module has failed. If a transmitter has failed, method1400may proceed to step1404, otherwise, method1400may return to the beginning.

At step1404, transponder102may determine if a spare transmitter associated with a spare channels in the first spare module is available. If the first spare module includes a spare transmitter, transponder102may direct electrical signals from the failed transmitter to the spare transmitter at step1406, such that traffic is rerouted to spare channels. Following step1406, transponder102may resume detecting failed transmitters at step1402. If no spare transmitters are available in the first spare module at step1404, at step1408, transponder102may direct electrical signals to a spare transmitter included in the second spare module, such that traffic is rerouted to a spare channel associated with the second spare module

At step1410, transponder102may determine which module or modules include the most failed transmitters. At step1412, transponder102may also determine the number of active, operational transmitters in the module or modules that include the most failed transmitters. In another embodiment, transponder102may perform steps1410and1412in reverse order or simultaneously.

At step1414, if the number of available spare transmitters associated with spare channels available in the second spare module is greater than the number of active, operational transmitters in the module or modules that include the most failed transmitters, method1400may return to step1402and transponder102may monitor for more failed transmitters. Otherwise, method1400may proceed to step1416.

At step1416, transponder102may indicate that one or more modules need to be replaced. As noted above, once only the number of available spare transmitters in the second spare module is less than or equal to the number of active, operating transmitters in the WDM module or modules with the most failed transmitters, one or more modules with failed transmitters may need to be replaced before another transmitter fails in order to prevent bandwidth loss.

At step1418, transponder102may indicate which modules need to be replaced and also may indicate the priority of replacement of modules (e.g., replacement of modules with the largest number of failed transmitters first). Following step1418, the modules with failed transmitters may be replaced and method1400may end.

In the event that the transponder determines there are no spare channels available and in actuality there will be un-used transmitters available to carry traffic, transponder102may still redirect traffic from additional failed transmitters. In this situation, repairing the system without capacity reduction may become impossible but reduction of capacity can be delayed and a critical-level alarm can be raised, providing time to find alternate solutions to preserve bandwidth.

Additions, modifications or omissions may be made to method1400without departing from the scope of the disclosure. For example, steps1416and1418may be combined or performed in reverse order than that described. Additionally, transponder102may determine that modules need to be replaced once electrical signals are sent to one transmitter in the second spare module, allowing for replacement of any module with failed transmitters without prioritizing the order of replacement. Such an implementation may eliminate the need to perform steps1410,1412and1414. Also, If the policy is to maintain a state where the traffic is protected, the warning or alarm to replace modules should be given before the last spare channel is used. Additionally, the transponder may redirect traffic to spare channels even if this would make it impossible to replace WDM modules without reducing bandwidth.

FIG. 15illustrates an example method1500for replacing modules with failed transmitters in accordance with step1420of method1400.

Method1500may begin and, at step1502, transponder102may route all electrical signals away from the active transmitters of the module to be replaced to the available spare transmitters in the second spare module. Consequently, the traffic may be rerouted to the channels associated with the second spare module.

At step1504, the defective module may be removed, and at step1506a new module may be inserted in the slot previously occupied by the defective module.

At step1508, transponder102may direct the electrical signals that were originally associated with the defective module to the transmitters included in the new module, to now route traffic to the channels associated with the new module. At step1510, it may be determined if all of the defective modules have been replaced. If all the defective modules have been replaced, method1500may end, otherwise, method1500may return to step1502.

Additions, modifications or omissions may be made to method1500without departing from the scope of the disclosure. For example, method1500may be utilized to replace fewer than all of the defective modules. Additionally, method1500may include steps indicating the priority of each module to be replaced.