Multichannel optical transmitter and apparatus in a WDM transmission system

Abstract

The present disclosure relates to multi-channel optical transmitters and apparatuses in WDM transmission systems. A GT etalon-based dispersion compensator is disclosed that can be utilized in combination with a wavelength division multiplexer at the transmitter location to provide a degree of pre-compensation for signals operating at wavelengths known to experience dispersion between the transmitter and receiver locations. The GT etalon-based dispersion compensator utilizes a separate dispersion compensator configured as a transmissive device by using a polarization beam splitter, a GT etalon, and a pair of quarter-wave plates in a manner such that the output signal path remains collinear with the input signal path and also preserves the linear polarization state of the propagating signal. Multiple of these transmissive dispersion compensators can be cascaded in a back-to-back arrangement within the signal path of a particular channel to provide a greater degree of pre-compensation for wavelengths known to be more susceptible to dispersion compensation.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Provisional Application No. 63 / 678,015, filed on July 31, 2024, and incorporated herein by reference. Technical Field

[0003] This disclosure relates to optical communication systems, and more specifically to the design of a compact dispersion compensation arrangement based on a Gilles-Turno (GT) etalon for use in multichannel environments of wavelength division multiplexing (WDM) optical communication systems. Background Technology

[0004] Dispersion is typically caused by the slightly different group velocities of different frequency components of an optical signal as they propagate through a dispersive medium. Therefore, the different frequency components of the transmitted optical signal will propagate at different speeds and arrive at the receiver at slightly different times. Consequently, the optical signal pulse broadens and loses its shape as it propagates along the fiber optic span between the transmitter and receiver. When the pulse broadening becomes excessive, adjacent pulses begin to interfere, thus limiting the maximum usable data rate without causing excessively high bit error rates.

[0005] In optical systems that support multiple wavelengths (i.e., multiple channels) between the transmitter and receiver, dispersion-related problems are exacerbated because different wavelengths experience different amounts of dispersion over the same span. In most cases, optical systems supporting multiple wavelengths utilize wavelength-based multiplexers and demultiplexers at both the transmitter and receiver, enabling a single communication fiber to support the transmission of all wavelengths.

[0006] To date, arrangements for addressing dispersion in WDM optical communication systems have relied on the use of specialized transmission fibers providing a certain degree of wavelength-specific compensation, or on the use of individual electronically based circuit arrangements at the receiver, in conjunction with each demultiplexing channel, to correct for dispersion accumulated along the signal path. Fiber-based solutions using dispersion-compensating fibers and / or fiber Bragg gratings (FBGs) are reliable passive components; however, as the number of “paths” (channels) in a system continues to increase, utilizing fiber-based solutions within a standard small form factor (SFP) footprint becomes difficult. For example, it has been found difficult to implement fiber-based solutions in current eight-path (8-channel) SFP (OSFP) optical transceiver configurations. Advanced systems can utilize digital signal processor (DSP) components within the receiver to perform electronic dispersion compensation. These DSP-based receivers are inherently complex and expensive.

[0007] In other words, these two methods are not only difficult to implement, but also increase the cost and size requirements of the system. These problems will become even more pronounced as newer systems are developed to support an ever-increasing number of independent channels. Summary of the Invention

[0008] This paper discloses the design of a compact dispersion compensation component that can be incorporated into a multi-channel optical transmitter assembly in a manner that provides channel-specific compensation before transmitting multi-channel signals into a network. Specifically, a dispersion compensator based on a GT etalon is disclosed, which can be used in combination with a wavelength division multiplexer at the transmitter location to provide a degree of pre-compensation for signals that are known to operate at wavelengths that undergo dispersion between the transmitter and receiver locations.

[0009] In one implementation, the dispersion compensator based on the GT etalon utilizes a separate dispersion compensator configured as a transmissive device using a polarization beam splitter, a GT etalon, and a pair of quarter-wave plates, such that the output signal path remains collinear with the input signal path while also maintaining the linear polarization state of the propagating signal. Multiple of these transmissive dispersion compensators can be cascaded back-to-back within the signal path of a specific channel to provide a greater degree of pre-compensation for wavelengths known to be more susceptible to dispersion compensation.

[0010] In another embodiment, the integrated arrangement of the Z-block configured wavelength division multiplexer and the GT-based etalon dispersion compensator is considered to produce a compact arrangement that performs both functions within a multi-channel optical transmitter.

[0011] An example could take the form of a multichannel optical emitter comprising a laser engine, a wavelength division multiplexer, and a dispersion compensator based on a GT etalon. The laser engine comprises components that operate at different wavelengths and generate wavelengths in the range λ1-λ2. N Multiple N individual laser devices operate on multiple N optical signals (also considered as multiple N channels), each individual laser device responding to a unique input data signal. The wavelength division multiplexer receives the multiple N optical signals as input and combines them to produce a single N-channel output signal, which is used for transmission along the fiber optic signal path. A dispersion compensator based on the GT etalon is positioned between the laser engine and the wavelength division multiplexer, and includes components along the range λ1-λ2. N Each GT etalon device is configured within a signal path associated with an identified wavelength that undergoes dispersion during transmission along the fiber optic signal path. Each GT etalon device produces phase-shift pre-distortion for a selected wavelength of signal passing through the GT etalon device, and the number of GT etalon devices configured along each channel depends on the dispersion level.

[0012] Other and additional embodiments and advantages of the dispersion compensation arrangement based on the GT etalon disclosed will become apparent in the following discussion and with reference to the accompanying drawings. Attached Figure Description

[0013] Now refer to the attached diagram,

[0014] Figure 1 This is a simplified top view of an example 8-channel optical emitter configured to incorporate a dispersion compensator based on a GT etalon.

[0015] Figure 2 It can be used Figure 1 Detailed illustration of an example of a transmission-type dispersion compensator for an emitter;

[0016] Figure 3 yes Figure 1 Side view of the arrangement;

[0017] Figure 4 It is the dispersion response associated with the use of a pair of cascaded dispersion compensation elements based on GT etalon;

[0018] Figure 5 It is similar to Figure 4 The dispersive response, but in this case it is associated with a set of eight elements;

[0019] Figure 6 Another dispersive response is shown, in which the vernier effect associated with multiple overlapping responses is used to produce a precise, tunable passband;

[0020] Figure 7 This is another example of an embodiment of the present disclosure, illustrating an integrated combination of a wavelength division multiplexer and a dispersion compensator based on a GT etalon; and

[0021] Figure 8 It is to utilize Figure 7 A simplified diagram of the integrated optical transmitter shown. Detailed Implementation

[0022] A method is proposed to address the problem associated with wavelength-dependent dispersion compensation by incorporating one or more GT etalon-based dispersion compensators along each channel in a multi-channel optical transmitter of a WDM optical communication system. Figure 1This is a simplified top view of an example 8-channel optical transmitter 10 configured to incorporate a dispersion compensator based on a GT etalon along a selected signal path, thereby providing a degree of pre-compensation for the different wavelengths before multiplexing them onto the output signal path. The transmitter 10 includes a laser engine component 12 for generating a parallel set of eight optical data signals S1-S8 (8 in this case, N overall) based on a set of digital (electrical) data streams D1-D8. Data streams D1-D8 are used in this arrangement to modulate an array of eight individual lasers 131-138 operating at different wavelengths λ1-λ8. Other active laser source arrangements can be used; for example, distributed feedback lasers or externally modulated lasers. A wavelength multiplexer 14 is configured to be optically aligned with the laser engine 12 and operates in a known manner to combine the individual signals operating at wavelengths λ1-λ8 onto a single output path O, as shown.

[0023] In this specific example, multiplexer 14 includes: a first Z-block multiplexer configuration 16-1 for combining signals operating at wavelengths λ1-λ4 to generate a first multiplexed signal group M1; and a second Z-block multiplexer 16-2 for combining signals operating at wavelengths λ5-λ8 to generate a second multiplexed signal group M2. Z-blocks 16-1 and 16-2 are each angled as shown and (respectively) include reflective back surfaces 18-1 and 18-2 for combining signals as they zigzag within optical substrates 17-1 and 17-2. Combiner 19 is used to couple the multiplexed signal groups together to form a multi-channel output signal O. It should be understood that the illustrated Z-block configuration is merely one example of a wavelength multiplexer that can be used, and other arrangements known in the art (e.g., waveguide components of an array) may also be used in the disclosed pre-compensator arrangement.

[0024] According to the principles of this disclosure, by intentionally targeting known pathways from transmitter to receiver ( Figure 1 The signal path (not shown with an associated receiver) provides dispersion pre-compensation for those signal wavelengths particularly affected by dispersion, to enhance the operation of transmitter 10. The dispersion compensator 20, based on the GT etalon, provides... Figure 1 The image is shown positioned between laser engine 12 and multiplexer 14, wherein dispersion compensator 20 is configured to provide a separate pre-compensation amount (if necessary) for signals operating at each wavelength λ1-λ8, wherein the pre-compensation can be considered to cancel out a portion of the dispersion that subsequently occurs during propagation along the signal path from transmitter 10 to receiver (not shown). That is, the pre-compensation alters the conventional shape of the signal pulse by adding a phase delay, wherein the dispersion experienced by the signal pulse along the transmission path acts to eliminate the added pre-compensation, restoring the signal pulse to its original form.

[0025] The disclosed GT etalon-based dispersion compensator 20 is shown as comprising a plurality of individual transmission dispersion compensators 22, which are positioned to receive output signals from individual laser diodes 13, wherein the number of individual dispersion compensators for each channel depends on the known dispersion experienced by the operating wavelengths for the different channels. In this arrangement, the dispersion compensator 20 also includes a lens array 24, wherein each laser 13 i The output passes through the associated collimating lens 24 before entering any dispersion compensator 22 that may be included along its signal path. i .

[0026] Combined with the following text Figure 2 The discussed transmissive dispersion compensator 22 operates according to its included GT etalon to introduce a controlled amount of phase shift into the transmitted optical signal. By knowing a priori the wavelength used for transmission along each channel, the number of individual dispersion compensators required to fully account for the amount of dispersion accumulated between the transmitter and receiver can be determined. The compact transmissive construction of the dispersion compensator 22 allows for a cascaded arrangement that occupies little space in the transmitter but provides the required amount of pre-compensation.

[0027] In such Figure 1 In the example arrangement shown, laser diodes 134 and 135 operate at wavelengths λ4 and λ5, which are known to exhibit maximum dispersion. Therefore, for this example, a pair of cascaded transmission dispersion compensators 22x and 22y are utilized along with each of these lasers, arranged as shown. Also... Figure 1 As shown, laser diodes 134 and 135 are positioned in the middle of the laser array; this is intentional to eliminate the need for the two output beams to bounce back and forth within Z blocks 16-1 and 16-2; instead, their pre-compensated beams pass directly through Z blocks 16-1 and 16-2 and enter the coupler 19.

[0028] In the opposite extreme case, laser diodes 131 and 138 are identified as operating at wavelengths exhibiting little (if any) dispersion along the signal path between the transmitter and receiver. Therefore, as Figure 1 As shown, no pre-compensation is required and no dispersion compensator 22 is positioned along these signal paths. A single transmission dispersion compensator 22 is shown used in conjunction with the remaining laser diode 13 to provide sufficient pre-compensation for signals operating at their specific wavelengths. Utilizing the GT-based etalon-based dispersion compensator 20 in this way is considered to achieve a compact and individually customized arrangement for mitigating dispersion within WDM communication systems.

[0029] Figure 2This is a schematic diagram of an example transmission dispersion compensator 22, which helps to understand the working principle of the dispersion compensation based on the GT etalon provided according to this disclosure. The transmission dispersion compensator 22 is shown as including a polarization beam splitter (PBS) 30 that receives a collimated linearly polarized output optical signal from a collimating lens 24 (see [link to diagram]). Figure 1 As indicated by the arrow, the linearly polarized optical signal is redirected downwards by the PBS 30 and then incident on the first quarter-wave plate (QWP) 32. The QWP 32 converts the polarization of the optical signal from linear to circular before passing it to the adjacent GT etalon element 34.

[0030] The GT etalon element 34 includes a transparent plate 36 having opposing reflective surfaces 38-1 and 38-2, wherein surface 38-1 is highly reflective (but not completely), while surface 38-2 is formed to have substantially 100% reflectivity. Due to multi-beam interference, light incident on surface 38-1 is guided into plate 36 and returns with an effective phase shift strongly dependent on the wavelength λ of the incident light. The thickness of plate 36 and its refractive index n are factors used to determine the amount of phase shift provided. As is known in the art, the GT etalon element 34 serves as a reflecting device, wherein both input and output light pass through reflective surface 38-1.

[0031] The phase-shifted output from the GT etalon 34 remains circularly polarized as it enters the QWP 32 for the second time. During this journey through the QWP 32, the circularly polarized phase-shifted signal becomes linearly polarized again, but in a direction orthogonal to the original input (e.g., S-linear input becomes P-linear output). This orthogonally polarized (and phase-shifted) signal passes directly through the PBS 30 and into the second QWP 40, which includes a highly reflective (100%) coating 42 on its opposing surfaces to redirect the signal so that it passes through the second QWP 40 again, resulting in an S-polarized phase-shifted output signal S. φ Adding this phase shift is understood as adding pre-compensation to the original input signal. Output signal S φ It can be guided to the subsequent transmission dispersion compensator 22 (in the following...) Figure 3 (as shown in the diagram), or it can be used as a pre-compensation signal as input to multiplexer 14.

[0032] Figure 3 This is a side view of the laser engine 12 and the dispersion compensator 20 based on the GT etalon, specifically showing the relationship with... Figure 1The components used in conjunction with the depicted "Channel 4" are shown. In this view, the laser engine 12 is shown as including a laser diode 134 that operates at a wavelength λ4, which is presumably susceptible to dispersion, as discussed above. The laser diode 134 is shown disposed on a base element 50, which in this specific example is positioned on a thermoelectric cooler (TEC) 52, which itself is positioned on a substrate 54. The collimating lens 244 of the GT etalon-based dispersion compensator 20 is positioned to be optically aligned with the output of the laser diode 134 to form a linearly polarized collimated beam input to the first transmissive dispersion compensator 22x.

[0033] As mentioned above Figure 2 As discussed in the schematic diagram, the optical signal passing through the first transmissive dispersion compensator 22x experiences a first phase shift due to the included GT etalon 34x. This phase-shifted output signal (which remains linearly polarized) then passes through the second transmissive dispersion compensator 22y, which introduces an additional phase shift. Another aspect of this disclosure is that the orientation of a particular collimating lens 24i relative to the subsequent transmissive dispersion compensator 22i can be adjusted to control the generated amount of phase shift, since the angle of incidence will be transmitted relative to the angle of incidence on the GT etalon 34i. In practice, in an example assembly procedure, the positioning of the collimating lens 24i relative to the transmissive dispersion compensator 22i can be actively adjusted until the desired amount of phase shift is achieved.

[0034] exist Figure 3 In the configuration shown, the first transmission dispersion compensator 22x and the second transmission dispersion compensator 22y are positioned on bases 56x and 56y, respectively, to maintain optical alignment, and are also shown mounted on TEC 52. This is only considered as an example, and in other arrangements, the dispersion compensator based on the GT etalon may not require the use of a TEC device to control its operating temperature.

[0035] Advantageously, and as Figure 3 As shown, the use of transmission-type dispersion compensators allows for a compact configuration, in which a pair of dispersion compensators 22x and 22y are shown adjacent to each other. Again, this is just one example; other arrangements can utilize several additional GT etalons arranged in a cascaded configuration to provide the required amount of pre-compensation for a selected optical signal.

[0036] Figure 4 An example dispersion response is shown that can be achieved by cascading a first transmission dispersion compensator 22x and a second transmission dispersion compensator 22y. In this case, their combination enables the formation of a relatively flat passband of 75 GHz near a wavelength of 1271 nm. Figure 5This is an example of the results associated with using a set of eight cascaded dispersion compensators, producing a passband with a width of 300 GHz. The vernier effect of the cascaded transmission dispersion compensator 22 is as follows: Figure 6 As shown in the figure, this illustrates the ability to provide dispersion compensation with high accuracy.

[0037] Figures 1 to 3 The example is associated with an implementation of multiplexer 14 and GT-based etalon-based dispersion compensator 20 utilizing separate components. This is considered only as an example, and specifically, as an example well-suited for providing pre-compensation in existing (conventional) multichannel optical emitters, including installed systems.

[0038] Figure 7 Another example of providing pre-compensation in a multi-channel optical emitter is shown, where multiplexer functionality and GT-based etalon-based dispersion compensation are integrated into a single component. Specifically, Figure 7 The figure illustrates an integrated multiplexer / pre-compensator 70 as a single structure comprising a Z-block multiplexer 72 and a dispersion compensator 74 based on a GT etalon. The Z-block multiplexer 72 includes an angled optical substrate 76 that allows wavelengths (shown here as λ1-λ4) to be combined along a single output path. As shown, a set of thin-film filters 78 are disposed along the input surface 73 of the multiplexer 72 and are designed to transmit a specific wavelength while reflecting all other wavelengths. For example, thin-film filter 78-1 is designed to transmit wavelength λ2 and reflect at least wavelength λ1; similarly, thin-film filter 78-2 is designed to transmit wavelength λ3 and reflect at least wavelengths λ1 and λ2.

[0039] A dispersion compensator 74 based on a GT etalon is shown disposed along the output surface 75 of the multiplexer 72. As discussed below, the dispersion compensator 74 includes a set of three separate GT etalon devices 80-1, 80-2, and 80-3, which interact with the signal emitted from the output surface 75 of the multiplexer 72 in such a way that they ultimately produce a multiplexed output beam with different pre-compensation amounts applied to each individual wavelength.

[0040] Specifically, the dispersion compensator 74 includes a single optical plate 82, wherein a set of three separate reflectors 84-1, 84-2, and 84-3 are disposed at defined positions along the output surface 83 of the optical plate 82, which are the positions of the GT etalon devices 80-1, 80-2, and 80-3. A set of partially reflective opposing reflectors 86-1, 86-2, and 86-3 are positioned to complete the GT etalon structure and are disposed at the interface between the optical substrate 76 of the multiplexer 72 and the optical plate 82 of the dispersion compensator 74.

[0041] A set of three separate GT etalon devices 80-1, 80-2, and 80-3 are arranged in a cascaded configuration, wherein, in this example, the signal operating at λ1 will pass through all three etalon devices before exiting from the integrated multiplexer / pre-compensator 70. Therefore, in the assembly of the structure, the wavelength requiring the highest level of pre-compensation will be used as λ1. Reference Figure 7 The signal operating at λ1 first passes directly through multiplexer 72 and is then guided to the first GT etalon device 80-1, where it undergoes an initial phase shift via multi-beam interference. This phase-shifted beam is then guided back to multiplexer 72 and reflected by the first thin-film filter 78-1, thereby being redirected back to multiplexer / pre-compensator 70, and specifically back to the second GT etalon device 80-2 (and further phase-shifted as described above). The same process is repeated, wherein the second-shifted signal at λ1 is reflected by the second thin-film filter 78-2, further phase-shifted within the third GT etalon device 80-3, and finally reflected by the third thin-film filter 78-3 onto the output signal path O.

[0042] The wavelength required to pass through the two cascaded GT etalon devices is designated as λ2, where, as shown, this input passes through the first thin-film filter 78-1 and is directed into the second GT etalon device 80-2. The phase-shifted signal at λ2 then exits from the dispersion compensator 74 and is reflected by the thin-film filter 78-2 of the multiplexer 72, thereby being redirected to the third GT-based etalon 80-3. The signal operating at λ3 is shown as passing only through the GT-based etalon 80-3 before being redirected by the third thin-film filter 78-3 along the output signal path O. Finally, the signal operating at λ4 is shown as passing through the final thin-film filter 78-3 and joining the output signal path O without passing through any GT-based etalon pre-compensation device.

[0043] Figure 8 This is an example diagram of a compact optical transmitter 90 based on the integrated multiplexer / pre-compensator 70 discussed above. In this embodiment, a pair of integrated multiplexers / pre-compensators 70-1, 70-2 are used, each receiving a set of four input signals to provide a comparison with the eight-channel optical transmitter 10 described above. Here, this pair of integrated multiplexers / pre-compensators 70-1, 70-2 is assembled into a component 80 disposed between the laser engine 12 and the output combiner 19. Again, the illustrative use with the eight-channel transmitter is merely an example. The integrated structure of this embodiment is considered capable of achieving large-count multiplexing-demultiplexing operations without encountering the physical size and optical alignment problems of the prior art, while still providing compensation capabilities for a large number of individual channels.

[0044] Although this disclosure has been described and illustrated herein with reference to its preferred embodiments and specific examples, it will be apparent to those skilled in the art that other embodiments and examples can perform similar functions and / or achieve similar results. All such equivalent embodiments and examples are to be considered fully encompassed within the scope of the appended claims.

Claims

1. A multi-channel optical transmitter, comprising: A laser engine comprises N individual laser devices operating at different wavelengths and generating N optical signals, wherein each individual laser device responds to a unique input data signal, the N optical signals being at wavelengths λ1-λ2. N The operation is performed on N channels and treated as multiple channels; A wavelength division multiplexer receives N optical signals as input and combines them to generate a single N-channel output signal, the single N-channel output signal being transmitted along an optical fiber signal path; and A dispersion compensator based on the GT etalon is disposed between the laser engine and the wavelength division multiplexer. The dispersion compensator based on the GT etalon includes components along the range λ1-λ2. N Each GT etalon device is configured within a signal path associated with an identified wavelength, the identified wavelength undergoing dispersion during transmission along the fiber optic signal path, wherein each GT etalon device produces phase-shift pre-distortion for a selected wavelength of signal passing through each GT etalon device, and the number of GT etalon devices configured along each channel depends on the level of dispersion experienced by the wavelength utilized by the channel.

2. The multi-channel optical transmitter according to claim 1, wherein, The dispersion compensator based on the GT etalon includes multiple transmission dispersion compensators, each of which includes: A polarization beam splitter that responds to a linearly polarized input signal propagating along the optical axis of the multi-channel optical transmitter and redirects the linearly polarized input signal along an orthogonal signal path; The first quarter-wave plate is converted into a circularly polarized signal in response to the redirected linearly polarized input signal; A GT etalon, disposed adjacent to the first quarter-wave plate, generates a phase-shifted version of the circularly polarized signal as an output in response to the circularly polarized signal, wherein the reflective surface of the GT etalon guides the phase-shifted version back through the first quarter-wave plate, thereby converting it back into a linearly polarized signal including phase-shift characteristics, and then feeds it into the polarization beam splitter. A second quarter-wave plate, disposed adjacent to the polarization beam splitter and configured to intercept linearly polarized phase-shifted signals; and A high-reflectivity element is disposed on the second quarter-wave plate, wherein the combination of the second quarter-wave plate, the high-reflectivity element, and the polarization beam splitter is used to return the phase-shifted signal to its original linear polarization state, and the phase-shifted signal having the original linear polarization state is then emitted from the polarization beam splitter along the optical axis as an output signal from the dispersion compensator based on the GT etalon.

3. The multi-channel optical transmitter according to claim 2, wherein, A cascaded arrangement of two or more transmission dispersion compensators is set in the signal path of a selected channel to provide greater pre-compensation for optical signals propagating at wavelengths known to experience significant dispersion.

4. The multi-channel optical transmitter according to claim 1, wherein, The wavelength division multiplexer includes a Z-block multiplexer configuration.

5. The multi-channel optical transmitter according to claim 4, wherein, The dispersion compensator based on the GT etalon is configured and integrated with the Z-block multiplexer to form a single unit.

6. The multi-channel optical emitter according to claim 4 or 5, wherein, The dispersion compensator based on the GT etalon includes: An optical plate is disposed at an angle along the output surface of the Z-block multiplexer; A plurality of M highly reflective elements are arranged at intervals on the output surface of the optical plate, each individual highly reflective element defining a first reflective surface of the GT etalon; and A plurality of M input reflective elements are arranged along the interface between the Z-block multiplexer and the optical plate, and the plurality of M input reflective elements and the plurality of M high reflective elements are aligned in such a way that a plurality of M cascaded GT etalon devices are generated along the extent of the optical plate.

7. An apparatus for use in a WDM transmission system, comprising: Wavelength division multiplexer, receiving signals at multiple different wavelengths λ1-λ N The operation uses multiple N optical signals as inputs to combine the multiple N optical signals to generate a single N-channel output signal, which is used for transmission along the optical fiber signal path. as well as A dispersion compensator based on the GT etalon is disposed at the input of the wavelength division multiplexer. The dispersion compensator based on the GT etalon includes components along the range λ1-λ2. N Each GT etalon device is configured within a signal path associated with an identified wavelength, the identified wavelength undergoing dispersion during transmission along the fiber optic signal path, wherein each GT etalon device produces phase-shift pre-distortion for a selected wavelength of signal passing through each GT etalon device, and the number of GT etalon devices configured along each channel depends on the level of dispersion experienced by the wavelength utilized by the channel.

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