Patent Publication Number: US-2015086207-A1

Title: Comb laser optical transmitter and roadm

Description:
BACKGROUND INFORMATION 
     With the proliferation of fiber optic networks and the wider adoption of high-speed networking, the demand for systems using lasers at different wavelengths is increasing. For example, Wavelength Division Multiplexing (WDM), Coarse Wavelength Division Multiplexing (CWDM), and Dense Wavelength Division Multiplexing (DWDM) systems increase data capacity by using multiple channels over a single fiber, where each channel may be associated with a particular wavelength. Different wavelengths may be added or dropped to or from a WDM/CDWM/DWDM signal using a Reconfigurable Optical Add-Drop Multiplexer (ROADM). Transmitters used with such systems may include tunable lasers that are set based on the wavelength of the channel to which they are connected. These tunable lasers can be expensive, and may be susceptible to drifts in wavelength due, for example, to variations in environmental conditions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a drawing illustrating an exemplary network in which embodiments described herein may be implemented; 
         FIGS. 2  is a diagram showing differences between a tunable laser and a comb laser; 
         FIG. 3  is a block diagram illustrating an exemplary Optical Transmitter and ROADM which uses a comb laser; 
         FIG. 4  is a block diagram showing exemplary components of the Optical Transmitter and ROADM of  FIG. 3 ; 
         FIG. 5  is a block diagram illustrating exemplary components including photonic switching for the Optical Transmitter and ROADM of  FIG. 3 ; 
         FIG. 6  is a block diagram showing exemplary components including variable gain amplifiers for the Optical Transmitter and ROADM of  FIG. 3 ; 
         FIG. 7  is a block diagram illustrating exemplary components including those used for automatic gain control in the Optical Transmitter and ROADM of  FIG. 3 ; 
         FIG. 8  is a flowchart showing an exemplary process for the operation of the Optical Transmitter and ROADM of  FIG. 3 ; 
         FIG. 9  is a flowchart showing an exemplary process for the operation of the automatic gain control for the Optical Transmitter and ROADM of  FIG. 7 ; and 
         FIG. 10  is a block diagram of an exemplary controller for the Optical Transmitter and ROADM of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The following detailed description refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements. Also, the following detailed description does not limit the invention. 
     Embodiments provided herein relate to devices and methods implementing a comb laser for use in wavelength division multiplexed environments, such as, for example, CWDM, WDM, DWDM and/or ROADM applications. Coarse wavelength division multiplexing (CWDM), Wavelength division multiplexing (WDM) and dense WDM (DWDM) enable transmission of data signals having a number of different wavelengths into a single optical fiber. The comb laser generates a source beam which covers a range of wavelengths, which may be used to simultaneously provide multiple wavelengths for use in CWDM, WDM or DWDM systems. In an embodiment, the source beam of a comb laser is separated into multiple beams, where each beam may be centered a particular wavelength that may be thought of as separate channel. Upon separation, each beam is individually processed as a separate channel in a parallel manner. The processing includes, for example, separately adjusting the amplitude of each beam to correct wavelength dependent amplitude variations which may be present in the source beam. The processing may also include modulating each beam to encode information within each channel. The processing can further include the adding or dropping of wavelengths through various switching approaches, thus effectively adding or dropping individual channels according to the needs of the optical network. Once the processing of individual beams is complete, the beams may be combined into an output signal, such as, for example, a CDWM, WDM, or DWDM signal. 
       FIG. 1  is a block diagram of an exemplary network  100  in which embodiments described herein may be implemented. As shown, optical network  100  may include metro/regional networks  102 - 1  and  102 - 2 , long haul or ultra-long haul optical lines  104 , and edge network  106 . Depending on the implementation, optical network  100  may include may include additional, fewer, or a different configuration of optical networks and optical lines than those illustrated in  FIG. 1 . For example, in one implementation, optical network  100  may include additional edge networks and/or metro/regional networks that are interconnected by, for example, Synchronous Optical Network (SONET) rings and/or Optical Transport Networks (OTN). 
     Metro/regional network  102 - 1  may include optical fibers and central office hubs that are interconnected by the optical fibers. The central office hubs, one of which is illustrated as central office hub  108 - 1 , may include sites that house telecommunication equipment, including switches, optical line terminals, etc. In addition to being connected to other central offices, central office hub  108 - 1  may provide telecommunication services to subscribers, such as telephone service, access to the Internet, cable television programs, etc., via optical line terminals. Metro/regional network  102 - 2  may include similar components as metro/regional network  102 - 1  and may operate similarly. In  FIG. 1 , metro/regional network  102 - 2  is illustrated as including central office hub  108 - 2 , which may include similar components as central office hub  108 - 1  and may operate similarly. Long haul optical lines  104  may include optical fibers that extend from metro/regional optical network  102 - 1  to metro/regional optical network  102 - 2 . 
     Edge network  106  may include optical networks that provide user access to metro/regional optical network  102 - 2 . As shown in  FIG. 1 , edge network  106  may include access points  110 - 1  and  110 - 2  (e.g., office buildings, residential area, etc.) via which end customers may obtain communication services from central office hub  108 - 2 . 
     In  FIG. 1 , networks  102 - 1 ,  102 - 2 , and  106  may include ROADMs  112 - 1  through  112 - 5  (collectively “ROADMs  112 ” and individually “ROADM  112 - x ”). Each ROADM  112 - x  may add or drop optical signals of particular wavelengths to/from the network and provide for part of wavelength division multiplexing (WDM) in network  100 . The configuration of ROADMs  112  may be controlled remotely (e.g., from central office hub  108 - 1 ). In some implementations, data in network  100  may be transmitted using, for example, DWDM, which may use the C band (i.e., frequencies between 1530 and 1565 nanometers (nm)) and/or L band (i.e., wavelengths between 1565 and 1625 nm). 
       FIG. 2  is a diagram illustrating exemplary differences between tunable laser  202  and comb laser  206 . Tunable laser  202  may produce a source beam at a selected wavelength λ s . As shown in graph  204 , which depicts the source beam amplitude versus wavelength λ, the source beam wavelength is “tuned” from a range of wavelengths Δ λ  to the selected wavelength λ s . The range of wavelengths may include parts of C band, parts of L band, or combinations thereof; or the entire C band, the entire L band, or a combination thereof. The tuning of the wavelength may be externally commanded using a wavelength control signal. In practice, tunable laser  202  may tune the wavelength by controlling the physical length of a resonant cavity within the laser. This approach can limit the precision to which tunable laser  202  can select the wavelength. Accordingly, an error ε λ  may be associated with a shift in selected wavelength λ s  as shown in graph  204 . The error ε λ  may be dependent on thermal factors, which can motivate the use of precise temperature controls to reduce the error ε λ . However, such temperature controls can increase the cost and complexity of systems using tunable lasers  202 . Additionally, the control of tunable laser  202  is typically realized using circuits, which have components that may drift and introduce additional errors in the selected wavelength λ s . In practice, the wavelength errors may be compensated using filtering techniques which may reduce the efficiency of the system since filtering discards optical energy. 
     In contrast, comb laser  206  may produce a source beam which simultaneously includes multiple wavelengths over the range of wavelengths Δ λ . The range of wavelengths may include parts of C band, parts of L band, or combinations thereof; or the entire C band, the entire L band, or combinations thereof. As shown in graph  208 , the amplitude of the source beam produced by comb laser  206  may vary as a function of wavelength. However, as will be discussed in detail below, these variations may be addressed using amplitude compensation during processing. Systems using the comb laser  206  may save costs. One comb laser  206  can replace multiple tunable lasers  202 , since comb laser  206  produces a beam with multiple wavelengths. For example, as shown in graph  208 , comb laser  206  may produce wavelengths λ 1 , λ 2 , . . . , λ N , where δ λ  is the channel spacing. Additionally, comb laser  206  may not require precise thermal control to maintain wavelength accuracy, which results in reduced cost and less complexity. Moreover, systems using comb laser  206  may be more efficient. Instead of discarding unwanted wavelengths via filtering, different wavelengths are simultaneously used in a parallel manner, as will be discussed below in more detail. Finally, systems using comb lasers have the ability to quickly add or drop wavelengths using fast photonic switches. Aspects of systems using comb lasers  206 , including exemplary Optical Transmitters and ROADMs, are presented in more detail below. 
       FIG. 3  is a top level block diagram illustrating an exemplary Optical Transmitter and ROADM (Optical Tx/ROADM)  300  according to an embodiment. Components of Optical Tx/ROADM  300  include comb laser  206 , preprocessor  310 , wavelength separator  315 , processors  320 , and wavelength combiner  325 . These components may be configured in a manner as shown in  FIG. 3  and as described below. 
     The comb laser  206  provides a source beam having multiple wavelengths over a range as described above in relation to  FIG. 2 . In this manner, a single laser source may provide many wavelengths simultaneously for use in the Optical Tx/ROADM  300 . Comb laser  206  may be optically coupled to preprocessor  310 , which optically conditions the source beam prior to separating the source beam into multiple beams. The optical conditioning may include any form of optical processing which facilitates the separating process. For example, in an embodiment, preprocessor  310  includes a collimator, which aligns the source beam to improve beam separation. Preprocessor  310  may be optically coupled to wavelength separator  315 . Wavelength separator  315  receives the preprocessed source beam and separates it into multiple beams, where each separated beam is centered at a different wavelength λ i . Wavelength separator  315  may utilize any known optical components to perform the separation. In one embodiment, wavelength separator  315  uses a diffraction grating. Wavelength separator  315  is optically coupled to processors  320 , which receive each of the separated beams corresponding to the different wavelengths, and individually process the beams in a parallel manner. While shown in  FIG. 3  as separate entities for clarification, processors  320  may be realized in a single unit which can perform parallel processing of the beams. The processing includes, for example, separately adjusting the amplitude of each beam to correct wavelength dependent amplitude variations, modulating each beam to encode information within each channel, and adding or dropping wavelengths through various switching approaches. 
     Processors  320  may be optically coupled to wavelength combiner  325 , which merges the individually processed beams into a single output signal. Wavelength combiner  325  may include any optical component(s) suitable for merging the individual beams into a single optical beam having multiple wavelengths. In an embodiment, wavelength combiner  325  includes a collimator and a multiplexer to produce a DWDM output beam. As will be described below, the DWDM output beam may be further processed before being used in network  100 . 
       FIG. 4  is a block diagram showing exemplary components within an embodiment of Optical Tx/ROADM  400 . Optical Tx/ROADM  400  may include comb laser  206 , input collimator  410 , diffraction grating  415 , processor  460 , output collimator/multiplexer  440 , optical amplifier  445 , and filter  450 . 
     Processor  460  may include a plurality of optical processors, where each “leg” of processor  460  corresponds to a particular wavelength λ x , where x=1, . . . , N, and N is the total number of wavelengths. Each leg may be thought of as a separate channel. In this embodiment, each leg corresponding to λ x  includes collimator  420 - x , variable optical attenuator (VOA)  425 - x , modulator  430 - x , and collimator  435 - x . As used herein, the components within each leg of /processor  460  may collectively be referenced without the “-x” designation. For example, the modulators across all the legs of processor  460  may be referred to as “modulators  430 .” The components of Optical Tx/ROADM  400  may be configured in a manner as shown in  FIG. 4  and as described below. 
     Further referring to  FIG. 4 , comb laser  206  provides a source beam having multiple wavelengths to input collimator  410 . Input collimator  410  aligns the wavefronts of the source beam so they are approximately planar and properly focused. Input collimator  410  then passes the collimated source beam through diffraction grating  415 , which separates the source beam into multiple beams. While not depicted in  FIG. 4 , diffraction grating  415  may separate the different wavelengths by scattering them at different angles. Utilizing the collimated source beam facilitates the quality of beam separation because the collimated source beam has reduced divergence, and thus the source beam will impinge on diffraction grating  415  at the desired angle. Each separated beam is centered at a particular wavelength, and thus may be regarded as a separate optical channel. For example, as shown in  FIG. 4 , diffraction grating  415  produces N separate beams, where each separated beam is centered at λ x  (where x=1, . . . , N). Embodiments of Optical Tx/ROADM  400  may utilize a large number of separate wavelengths, such as, for example,  150  channels (N=150). Various types of diffraction gratings may be used to separate the source beam, such as, for example, an echelle grating and/or other low loss gratings and or interleavers. Diffraction grating  415  may be optically coupled to each leg of processor  460 , which is described in more detail below. 
     As exemplified in  FIG. 4 , each leg of processor  460  receives one of the N beams from diffraction grating  415  and processes the beam as a separate channel. Each separate channel x (where x=1, . . . , N) is associated with a corresponding wavelength (λ x ), and the processing of the N channels may be performed in parallel. Therefore, the N channels may be processed in a substantially simultaneous manner. However, depending upon the physical characteristics of the optical circuits and the components, the processing across all N legs may not be exactly simultaneous. Statistical variations in component values and path lengths, and/or non-ideal component characteristics (such as, for example, wavelength dependent delays and/or non-linear characteristics) may cause timing variability across the legs in processor  460  which may be compensated through further known processing techniques. For the embodiment shown in  FIG. 4 , aside from being assigned to different wavelengths, the legs in processor  460  may be structurally and functionally similar to each other. Accordingly, the description for each of the legs may be presented in the context of a single exemplary leg (hereinafter “Leg-x”) associated with the wavelength λ x . However, in alternate embodiments, the legs of processor  460  may be different from one another. 
     Leg-x may include collimator  420 - x  which is optically coupled to diffraction grating  415 . Collimator  420 - x  receives a beam centered at wavelength λ x  (hereinafter Beam-x) from diffraction grating  415 , and collimates Beam-x for alignment and focus. Collimator  420 - x  may be optically coupled to variable optical attenuator (VOA)  425 - x . In this embodiment, VOA  425 - x  may perform several functions. The first function of VOA  425 - x  includes attenuating the amplitude of Beam-x to adjust the power in Leg-x. The attenuation of particular wavelengths may be done at the request of the network (e.g., based on predetermined signal requirements). Alternatively, the amplitude of a particular wavelength may be adjusted to compensate for amplitude variations that vary with wavelength. Such variations may be introduced by some optical components in Optical Tx/ROADM  400 . For example, the output of diffraction grating  415  may not be uniform across all the wavelengths X 1-N , and can be corrected within each leg. In another example, wavelength dependent amplitude variations may be introduced into the source beam by comb laser  206 . Such amplitude variations are exemplified in graph  208  of  FIG. 2 , which shows an amplitude taper across the range of wavelengths A. 
     The second function that VOA  425 - x  may perform in this embodiment is to add or drop wavelength λ x  to accomplish ROADM functionality. Here, VOA  425 - x  may sharply attenuate Beam-x to a negligible amplitude in order to drop λ x . As will be discussed in reference to  FIG. 5 , faster add/drop functionality can be accomplished in a different embodiment by adding an additional switch in each processing leg. 
     Further referring to  FIG. 4 , VOA  425 - x  is optically coupled to modulator  430 - x , which modulates Beam-x to encode information therein and create a signal. Modulator  430 - x  may perform any type of modulation suitable for optical signals, which may include, for example,  10 Gb/sec- 100 Gb/sec modulation formats. These formats may further use, for example On-Off Keying ( 00 K), Quadrature Phase Shift Keying (QPSK), Differential Phase Shift Keying (DPSK), Quadrature Amplitude Modulation (QAM), or Orthogonal Frequency Division Multiplexing (OFDM) modulation techniques, or any suitable combinations thereof. Because the modulators  430  in each leg may separately modulate the beams for their corresponding wavelengths λ 1-N , a diverse mix of signals may be created. For this embodiment, the last component in Leg-x is collimator  435 - x , which is optically coupled to modulator  430 - x , and further aligns and focuses modulated Beam-x prior to combining the wavelengths λ 1-N  as described below. In an alternative embodiment, modulators  430  may switch places with collimators  420  in the legs of processor  460 . Thus, modulator  430 - x  may be optically coupled to diffraction grating  415  to receive Beam-x directly from diffraction grating  415 . The modulated Beam-x may be provided to VOA  425 - x , and then onto collimator  420 - x  for alignment and focus. 
     All of the legs corresponding to wavelengths λ 1-N  in processor  460  may be optically coupled to output collimator/multiplexer  440 , which combines all of the beams centered at wavelengths λ 1-N  to create a combined signal. The combined signal may be a WDM or a DWDM signal, depending upon the requirements of the network. The collimator/multiplexer may be optically coupled to optical amplifier  445 , which provides the combined optical signal with enough power for transmission over the network. The amplified optical signal may be further processed with gain-flattening filter  450 , which is optically coupled to optical amplifier  445 . The gain flattening filter  450  can compensate for any frequency alterations in the combined signal which may have been introduced by optical amplifier  445 . At this point, the combined signal is ready for transmission over the optical network. 
       FIG. 5  is a block diagram of an embodiment of an Optical Tx/ROADM  500  illustrating exemplary components which include photonic switches  505 . Optical Tx/ROADM  500  may include comb laser  206 , input collimator  410 , diffraction grating  415 , processor  560 , output collimator/multiplexer  440 , optical amplifier  445 , and filter  450 . 
     Processor  560  may include a plurality of optical processors, where each leg (Leg-x) of processor  560  is a separate channel which corresponds to a particular wavelength λ x  (where x=1, . . . , N and N is the total number of wavelengths). In the embodiment shown in  FIG. 5 , Leg-x includes collimator  420 - x , VOA  425 - x , modulator  430 - x , photonic switch  505 - x , and collimator  435 - x . Optical Tx/ROADM  500  may be configured in a manner as shown in  FIG. 5  and as described below. 
     For brevity, elements having reference numbers which were shown in previous drawings and described above will not be described again, unless such description is relevant to the explanation of the features particular to the Optical Tx/ROADM  500  shown in  FIG. 5 . 
     In processor  560 , photonic switch  505 - x  is added to Leg-x to provide drop/add functionality to Optical Tx/ROADM  500 . The photonic switch  505 - x  may be placed between modulator  430 - x  and collimator  435 - x . The photonic switch  505 - x  receives the modulated beam from modulator  430 - x , and can drop the wavelength by switching the modulated beam out of the signal path. Wavelength λ x  can be added by having photonic switch  505 - x  switch the modulated beam into the signal path, so it is provided to collimator  435 - 1 . The photonic switch may be a 1×2 switch, and may feature fast switching times (e.g., on the order of 50 μsec or less). 
     Moreover, in this embodiment, the VOA  425 - x  would not perform the drop/add functionality by changing the attenuation as described above in  FIG. 4 . Instead, VOA  425 - x  would only vary the attenuation to adjust the power of Beam-x. The photonic switch  505 - 1  can perform the drop/add functionality faster on the order of nanoseconds or femto seconds, and may provide higher isolation when a particular wavelength is dropped. To improve isolation of dropped wavelengths, in one embodiment, optical switches  505  may be coupled to a VOAs (not shown) to improve isolation. Thus, when a particular wavelength is dropped, it becomes “dark” over the fiber at the output. 
       FIG. 6  is a block diagram of an embodiment of an Optical Tx/ROADM  600  illustrating exemplary components which include variable gain amplifiers. Optical Tx/ROADM  600  may include comb laser  206 , input collimator  410 , diffraction grating  415 , processor  660 , output collimator/multiplexer  440 , optical amplifier  445 , and filter  450 . 
     Processor  660  may include a plurality of optical processors, where each leg (Leg-x) of processor  660  is a separate channel which corresponds to a particular wavelength λ x  (where x=1, . . . , N and N is the total number of wavelengths). In the embodiment shown in  FIG. 6 , Leg-x includes collimator  420 - x , variable optical attenuator  425 - x , modulator  430 - x , photonic switch  505 - x , variable optical gain amplifier  605 - x , and collimator  435 - x . Optical Tx/ROADM  600  may be configured in a manner as shown in  FIG. 6  and as described below. 
     For brevity, elements having reference numbers which were shown in previous drawings and described above will not be described again, unless such description is relevant to the explanation of the features particular to the Optical Tx/ROADM  600  shown in  FIG. 6 . 
     In processor  660 , variable optical gain amplifier  605 - x  is added to Leg-x to provide optical amplification for wavelength λ x . The variable optical gain amplifier  605 - x  may be placed between photonic switch  505 - x  and collimator  435 - x . The variable optical gain amplifier  605 - x  receives the beam from photonic switch  505 - x  and provides amplification to the modulated optical beam. The amplified beam may then be provided to collimator  435 - x . The gain of the variable gain optical amplifier  605 - x  may be adjusted based on the needs of the network for a particular wavelength λ x . As will be discussed below in relation to  FIG. 8 , variable optical amplifier  605 - x  may be adjusted under computer control to automatically adjust the gains of Beam x. 
       FIG. 7  is a block diagram of an embodiment of an Optical Tx/ROADM  700  illustrating exemplary components which include those used for automatic gain control. Optical Tx/ROADM  700  may include comb laser  206 , input collimator  410 , diffraction grating  415 , processor  760 , output collimator/multiplexer  440 , optical amplifier  445 , and filter  450 . 
     Processor  760  may include a plurality of optical processors, where each leg (Leg-x) of processor  760  is a separate channel which corresponds to a particular wavelength λ x  (where x=1, . . . , N and N is the total number of wavelengths). In the embodiment shown in  FIG. 7 , Leg-x includes collimator  420 -x, variable optical attenuator  425 - x , modulator  430 - x , photonic switch  505 - x , variable optical gain amplifier  605 -x, sensor  705 - x , controller  710 - x , and collimator  435 - x . Optical Tx/ROADM  700  may be configured in a manner as shown in  FIG. 7  and as described below. 
     For brevity, elements having reference numbers which were shown in previous drawings and described above will not be described again, unless such description is relevant to the explanation of the features particular to the Optical Tx/ROADM  700  shown in  FIG. 7 . 
     In processor  760 , sensor  705 - x  is placed within Leg-x after variable gain amplifier  605 - x  to measure the amplitude of Beam-x after amplification. Sensor  705 - x  provides amplitude information to controller  710 , so controller may change variable optical attenuator  425 - x  and/or variable gain amplifier  605 - x  to automatically control the gain of Beam-x. The controller  710  may control each leg separately by independently controlling variable optical attenuators  425  and variable gain amplifiers  605  for all the legs in processor  760 . A flow chart illustrating an exemplary method for automatically controlling the gain of Beam-x is described below with respect to  FIG. 9 . In an alternative embodiment, the sensors  704  in processor  760  may be replaced with a single sensor (not shown), which may determine gain distribution across each leg in processor  760  using a spectrum analyzer. The outputs of the spectrum analyzer may be provided to controller  710  to facilitate the gain control in each leg by adjusting variable optical attenuators  425  and/or variable gain amplifiers  605 . 
     While not explicitly shown in the Figures, other components in Optical Tx/ROADM  700  may be under computer control to facilitate its operation, such as, for example, diffraction grating  415 , modulators  430 , photonic switches  505 , and/or collimator/multiplexer  440 . Such control may facilitate the functionality of each of these devices as described above, and their control may be accomplished using known techniques. 
       FIG. 8  is a flowchart showing an exemplary method  800  for the operation of the Optical Tx/ROADM  300  of  FIG. 3 . Method  800  initially generates a comb source beam having a plurality of wavelengths (Block  802 ). This may be accomplished using comb laser  206 , which generates a source beam having a range of wavelengths. Method  800  then collimates the comb source beam to align and focus the beam for better separation of the wavelengths (Block  804 ). The source beam is separated into a plurality of beams, where each separated beam is centered at a different wavelength λ x  (where x=1, . . . , N and N is the total number of wavelengths) (Block  806 ). Method  800  then processes each beam separately (Block  808 ), where the processing may be done in a parallel manner. Method  800  then combines the plurality of processed beams into an output beam having a plurality of wavelengths (Block  810 ). 
       FIG. 9  is a flowchart showing an exemplary method  900  for the operation of the automatic gain control for the Optical Tx/ROADM  700 . Method  900  initially senses the amplitude of the processed beam associated with each leg in processor  760  (Block  902 ). Method  900  then compares the sensed amplitude to a threshold for each processed beam (Block  904 ). Method  900  then adjusts an amplifier gain (e.g., amplifiers  605 ) and/or a variable attenuator (e.g., VOA  425 ) for each processed beam in response to the comparing (Block  906 ). Method  900  may be implemented in software, and executed on a controller as described below in  FIG. 10 . 
       FIG. 10  is a block diagram of an exemplary controller  710  for the Optical Tx / ROADM  700  shown in  FIG. 7 . As shown in  FIG. 10 , controller  710  may include a bus  1030 , a processor  1020 , a memory  1025 , a sensor interface  1005 , an output interface  1010 , and communication interface  1015 . 
     Bus  1030  includes path that permits communication among the components of controller  710 . Processor  1020  may include any type of single-core processor, multi-core processor, microprocessor, latch-based processor, and/or processing logic (or families of processors, microprocessors, and/or processing logics) that interprets and executes instructions. In other embodiments, processor  1020  may include an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), and/or another type of integrated circuit or processing logic. 
     Memory  1025  stores information, data, and/or instructions which include code for the configuration assistant. Memory  1025  may include a dynamic, volatile, and/or non-volatile storage device. Memory  1025  may store instructions, for execution by processor  1020 , or information for use by processor  1020 . For example, memory  1025  may include a RAM, a ROM, a CAM, a magnetic and/or optical recording memory device, etc. 
     Component interface  1005  permits processor  1020  to interact with various components in controller  710 . For example, component interface  1005  permits the processor  1020  to receive information from sensors  705  regarding the amplitude of the beams in each leg of processor  760 . Component interface  1005  further permits controller  710  to issue commands to variable gain amplifiers  605  and variable optical attenuators  425  to control the gains in each leg based on the inputs received from sensors  705  and method  900 . Communication interface  1015  may include (e.g., a transmitter and/or a receiver) that enables controller  710  to communicate administration and control data devices and/or systems. 
     Controller  710  may perform operations relating to the automatic gain control of the beams associated with each leg in processor  760 . Controller  710  may perform these operations in response to processor  1020  executing software instructions contained in a computer-readable medium, such as memory  1025 . The software instructions contained in memory  1025  may cause processor  620  to perform the operations, such as, for example, those relating to process  900 . 
     In the preceding specification, various embodiments have been described with reference to the accompanying drawings. It will, however, be evident that various modifications and changes may be made thereto, and additional embodiments may be implemented, without departing from the broader scope of the invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than restrictive sense. For example, while series of blocks have been described with respect to  FIGS. 8 and 9 , the order of the blocks and/or signal flows may be modified in other implementations. Further, non-dependent blocks and/or signal flows may be performed in parallel. 
     It will be apparent that systems and/or methods, as described above, may be implemented in many different forms of software, firmware, and hardware in the implementations illustrated in the figures. The actual software code or specialized control hardware used to implement these systems and methods is not limiting of the embodiments. Thus, the operation and behavior of the systems and methods were described without reference to the specific software code--it being understood that software and control hardware can be designed to implement the systems and methods based on the description herein. 
     Further, certain portions, described above, may be implemented as a component that performs one or more functions. A component, as used herein, may include hardware, such as a processor, an ASIC, or a FPGA, or a combination of hardware and software (e.g., a processor executing software). 
     The terms “comprises” and/or “comprising,” as used herein specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof. Further, the term “exemplary” (e.g., “exemplary embodiment,” “exemplary configuration,” etc.) means “as an example” and does not mean “preferred,” “best,” or likewise. 
     No element, act, or instruction used in the present application should be construed as critical or essential to the embodiments unless explicitly described as such. Also, as used herein, the article “a” is intended to include one or more items. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise.