Management of gain equalization errors in optical communication systems.

Abstract

A technique for managing gain equalization errors in optical communication systems is provided. For example, a multi-stage gain correction filter may be configured to at least correct gain equalization errors caused by filters with insufficient resolution, such as typical non-reflective gain correction techniques used in optical communication systems. The multi-stage filter may include at least a wideband gain correction filter for correcting gain equalization errors across most of the transmission bandwidth and a narrowband gain correction filter for correcting errors in a narrow region of the bandwidth. One or more multi-stage filters may be implemented in a system repeater (which may be referred to as a hybrid GFF) or may be included in an independent entity (which may be referred to as a hybrid GEF).

Description

[Technical Field]

[0001] FIELD Embodiments of the present disclosure relate to the field of optical communication systems, and more particularly, to techniques for managing at least gain equalization errors in optical communication systems. [Background technology]

[0002] Long-haul optical communication systems, such as undersea optical communication systems, typically suffer from signal attenuation due to a variety of factors, including scattering, absorption, and bending. To compensate for attenuation, these long-haul systems may include a series of optical amplifiers spaced along the signal transmission path and configured to amplify or boost the optical signal to enable reliable detection at the receiver. Depending on the length of the transmission path, the number of optical amplifiers positioned along the path (and the distance between them) may vary.

[0003] An optical amplifier commonly used in long-distance optical communication systems may be an erbium-doped fiber amplifier (EDFA), which contains erbium (a rare earth element)-doped fiber and can enhance the intensity of incident optical signals of several wavelengths by pumping with a laser (e.g., in the 980 nm or 1480 nm wavelength regions). It is known that EDFAs output wavelength-related gain. Therefore, when an optical signal, such as a wavelength-division multiplexed (WDM) optical signal with multiple optical channels, is amplified by an EDFA, some wavelengths within the WDM signal wavelength range can be amplified more than other wavelengths.

[0004] To address nonuniformities in wavelength amplification, gain-flattening filters (GFFs) or gain-equalizing filters (GEFs) can be used to restore or correct wavelengths in optical signals to approximately the same or a specifically designed intensity, commonly known as gain equalization or gain flattening. However, achieving sustained equalization accuracy when correcting gain in long-distance optical communication systems can be challenging and demanding. For example, GFFs used in repeaters may have limited accuracy or resolution, and thus accumulated gain-related errors can be periodically cleaned by GEFs (usually located in individual GEF bodies) to keep the total gain error in the system within predefined design limits.

[0005] GFFs or GEFs can use various gain correction techniques, including, but not limited to, short-period Bragg grating filters (SP-BFGs), tilted Bragg grating filters (S-BGFs), long-period grating filters (LP-GFs), and thin-film filters (TFFs). Non-reflective filters, such as S-BGFs, LP-GFs, and TFFs, typically exhibit back reflection or little back reflection, and do not require an additional isolator at the GFF output of the EDFA (see Figure 10A). However, reflective filters, such as SP-BFGs, require an additional isolator at the GFF output (see Figure 10B). Such isolators increase undesirable losses in the propagating optical signal. Therefore, non-reflective GFFs or GEFs offer design advantages at both the component and system levels, as reducing the total number of passive components (e.g., optical isolators) can potentially reduce losses and increase cost and power efficiency in a design.

[0006] However, one drawback of using a non-reflective GFF or GEF is that the resolution of a non-reflective filter is typically worse than that of a reflective filter. As a result, gain errors caused by a non-reflective filter can have gain shape changes that may be too severe or too rapid for the cleaning filter to effectively repair, potentially causing gain changes in the receiver that significantly exceed design limits. Summary of the Invention [Problem to be solved by the invention]

[0007] A technique for managing gain equalization errors in an optical communication system is provided. For example, a multi-stage gain correction filter may be configured to at least correct gain equalization errors due to conventional non-reflective gain correction techniques used in the optical communication system. The multi-stage filter may include at least a wideband gain correction filter for correcting gain equalization errors over a majority of the transmission bandwidth and a narrowband gain correction filter for correcting errors in a narrow region of the bandwidth. One or more multi-stage filters may be implemented in a repeater (which may be referred to as a hybrid GFF) of the system or may be included in an independent body (which may be referred to as a hybrid GEF). [Means for solving the problem]

[0008] In one embodiment, the gain correction filter may include at least a first filter and a second filter different from the first filter. For example, the first filter may be configured to correct a gain equalization error in a first portion of the optical transmission bandwidth, and the second filter may be configured to correct a gain equalization error in a second portion of the optical transmission bandwidth, and the first portion of the optical transmission bandwidth may be wider than the second portion. The first correction filter and the second correction filter may have characteristics that are complementary to each other across the entire transmission bandwidth.

[0009] In another embodiment, the method may include at least correcting a gain equalization error in a first portion of the optical transmission bandwidth with a first filter and correcting a gain equalization error in a second portion of the optical transmission bandwidth with a second filter. For example, the first filter may be different from the second filter, and the first portion of the optical transmission bandwidth may be wider than the second portion.

[0010] In a further embodiment, a system includes at least one repeater disposed and spaced apart along an optical fiber cable, the at least one repeater may include a plurality of Erbium-doped fiber amplifiers (EDFAs) and may further include a plurality of hybrid gain correction filters, each of the plurality of hybrid gain correction filters coupled to an output of a respective EDFA of the at least one repeater. For example, each hybrid gain correction filter may include at least a first filter and a second filter different from the first filter, the first filter configured to correct gain equalization errors in a first portion of an optical transmission bandwidth, and the second filter configured to correct gain equalization errors in a second portion of the optical transmission bandwidth. The first portion of the optical transmission bandwidth may be wider than the second portion. [Brief explanation of the drawings]

[0011] [Figure 1] 1 illustrates an exemplary optical communication system. [Figure 2] 1 shows an example of increased gain equalization error. [Figure 3] 1 shows an example of gain equalization using a hybrid filter. [Figure 4A] 1 illustrates a first exemplary hybrid filter. [Figure 4B] 10 illustrates a second exemplary hybrid filter. [Figure 5] 1 illustrates an exemplary hybrid GFF deployed in a repeater. [Figure 6] An exemplary hybrid GEF placed in a GEF body is shown. [Figure 7]1 illustrates an exemplary hybrid GFF embodiment. [Figure 8] 1 shows a first exemplary hybrid GEF embodiment. [Figure 9] 1 shows a second exemplary hybrid GEF embodiment. [Figure 10A] 1 shows an EDFA with a non-reflective GFF. [Figure 10B] 1 shows an EDFA with a reflective GFF. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention relates to techniques for managing, correcting, or otherwise coordinating undesired gain equalization errors in optical communication systems that use or implement at least conventional non-reflective gain flattening or equalization techniques. According to embodiments, a multi-stage filter (which may be referred to herein as a "hybrid" filter, hybrid GFF, or hybrid GEF) can combine at least wideband and narrowband filtering capabilities to correct or substantially smooth any undesired changes in the gain shape. For example, the multi-stage filter may include at least two different filters: a wideband gain correction filter configured to at least cover and correct the gain across the entire (or nearly the entire) optical transmission bandwidth, and a narrowband gain correction filter configured to separate and correct the gain across a narrow range of the transmission bandwidth. As described in more detail below, undesired gain changes resulting from the use of at least conventional non-reflective gain flattening or equalization techniques may exhibit an elevated slope (e.g., expressed in dB / nm) and typically occur across a relative region of the optical transmission bandwidth.

[0013] In an embodiment, each filter of a multi-stage filter can be arranged in a different manner: first a wideband filter, then a narrowband filter, or vice versa. Also, each filter of a multi-stage filter can be based on at least a non-reflective or reflective filter technology. For example, the wideband filter can be based on a reflective technology, which may require an isolator disposed between the wideband filter and the narrowband filter to reduce interference from back reflections. In another example, both the wideband filter and the narrowband filter can be based on a non-reflective technology, which may not require an isolator disposed between them.

[0014] It will also be appreciated that two or more filter stages of a multi-stage filter may be combined into a single package to save at least space and assembly costs (e.g., two or more TFFs may be efficiently mounted or positioned within a single case). It will further be appreciated that one or more filters of a multi-stage filter may be chirped or non-chirped, where, for example, the chirp may be uniform across the entire bandwidth or may be variable.

[0015] In further embodiments, one or more multi-stage filters can be arranged or configured in an optical communication system in various ways. For example, a multi-stage filter can be arranged at the output of each corresponding EDFA of a repeater. In another example, one or more multi-stage filters can be arranged in a separate GEF body, where the entire GEF body can be coupled to each of "N" repeaters, where N is a preset or predefined value, with each multi-stage filter of the GEF body coupled to each EDFA output of the repeater. For ease of interpretation of this disclosure, a multi-stage filter arranged in a repeater may be referred to as a hybrid GFF, and a multi-stage filter arranged in a GEF body may be referred to as a hybrid GEF.

[0016] The present invention will now be described more fully hereinafter with reference to the drawings, in which preferred embodiments of the invention are shown. However, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. On the contrary, these embodiments are provided so that the present invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, like reference numerals always refer to like elements.

[0017] 1 illustrates an exemplary bidirectional optical communication system 101 capable of transmitting large amounts of data over long distances using high-bandwidth fiber. Bidirectional data transmission can be achieved by configuring fiber pairs within an optical cable and transmitting one or more channels (e.g., wavelength division multiplexed channels) per fiber pair.

[0018] As shown, optical communication system 101 may include terminals 103 and 105 connected by two unidirectional optical paths 111, 121, which together form a bidirectional fiber pair. Optical path 111 may transmit information in one direction (e.g., to the right) from a transmitter 113 at terminal 103 to a receiver 115 at terminal 105. Optical path 121 may transmit information in the other direction (e.g., to the left) from a transmitter 125 at terminal 105 to a receiver 123 at terminal 103. For terminal 103, optical path 111 is the outbound path and optical path 121 is the inbound path. Optical path 111 may include fibers 117-1 through 117-n and optical amplifiers 119-1 through 119-n, and optical path 121 may include fibers 127-1 through 127-n and optical amplifiers 129-1 through 129-n. One or more of optical amplifiers 119-1 through 119-n and 129-1 through 129-n may be EDFAs. It will be appreciated that in some examples, transmitter 113 and receiver 123 may be housed together in a transponder at terminal 103, and similarly, transmitter 115 and receiver 125 may be housed together in a transponder at terminal 105.

[0019] Optical path pairs (e.g., optical paths 111, 121) can be configured as a group of amplifier pairs 119-1 to 119-n and 129-1 to 129-n within repeaters 131-1 to 131-n. The repeaters 131-1 to 131-n are connected via paired fibers 117-1 to 117-n and 127-1 to 127-n, which may be included in an optical fiber cable with fibers supporting additional path pairs. Each repeater 131 may include one pair of amplifiers 119, 129 for each path pair and may include additional amplifiers for additional path pairs. The optical amplifiers 119, 129 can be EDFAs or other rare-earth doped fiber amplifiers such as Raman amplifiers or semiconductor optical amplifiers (SOAs). Paths 133-1 through 133-n may be coupled between optical paths 111, 121, for example, to one or more of repeaters 131-1 through 131-n. It will be understood that the terms "couple" or "coupled," as used in this disclosure, broadly refer to any connection, connecting, coupling, link, or linkage, and do not necessarily imply that coupled components or elements are directly connected to one another, whether direct or indirect, and whether wired or wireless.

[0020] Although an exemplary embodiment of optical communication system 101 has been shown and described, variations of optical communication system 101 are within the scope of this disclosure. Optical communication system 101 may include, for example, more optical path pairs and more or fewer repeaters. Alternatively, optical communication system 101 may not include any optical amplifiers, or may include, rather than optical amplifiers, optical pump power sources suitable for achieving optical gain through Raman amplification in the fiber connecting the repeaters or in the fiber contained within one or more repeaters 131.

[0021] It will also be understood that a transmitter, a receiver, a transponder including a transmitter and a receiver, or any other suitable device for transmitting and receiving data may include at least one memory and one or more processors (e.g., a CPU, an ASIC, an FGPA, any conventional processor, etc.) for executing instructions stored in the memory.

[0022] FIG. 2 shows an example of an increased gain equalization error 200 due to a conventional non-reflective gain compensation filter (e.g., GFF, GEF) according to an embodiment. For ease of interpretation, the example is based on the accumulated gain equalization error after 12 repeaters (e.g., 12 spans). As shown in the upper half of FIG. 2, the gain error (e.g., in dB) has a rapid or relatively drastic change between the 1525 nm wavelength and the 1530 nm wavelength, as indicated by the dotted box. It can be seen that as the optical signal is amplified through more repeater spans, this change in the residual shape of the gain error can become more drastic.

[0023] When the amplified optical signal passes through a conventional non-reflective gain correction filter (which may be a GFF if located in the repeater or a GEF if located in a separate GEF body) after the 12 repeaters, the equalization error output by the conventional filter may increase at one or more opposite or extreme regions of the optical bandwidth. System designs using reflective gain correction filters may also increase the equalization error. For example, as shown in the lower half of Figure 2, the gain equalization error increases significantly at the left side of the bandwidth, as indicated by the dotted box. As discussed above, errors such as the increased gain equalization error shown can propagate through the optical communication system and cause gain changes significantly exceeding the design limits associated with the system receiver(s).

[0024] 3 shows an example of gain equalization 300 using a hybrid gain correction filter according to an embodiment. For ease of interpretation, the gain equalization errors accumulated in the 12 repeaters described with reference to FIG. 2 above are used to describe the hybrid gain equalization 300 of FIG.

[0025] As shown in the figure, the hybrid gain correction filter may be a multi-stage filter and may include at least filters 302 and 304. For example, filter 302 may be a wideband gain correction filter (which may be simply referred to as a wideband filter in this disclosure), and filter 304 may be a narrowband gain correction filter (which may also be referred to as a narrowband filter). Wideband filter 302 may correct or equalize gain shape variations (e.g., gain shape errors) across most (if not all) of the bandwidth, as shown by the solid line (the shape of wideband filter 302) in the diagram on the right. Thus, the output of wideband filter 302 may exhibit an equalization error shape that is nearly flat across most or all of the transmission bandwidth and has low peak-to-peak variations.

[0026] In a further example, the narrowband filter 304 can correct or equalize gain shape variations (e.g., gain shape errors) in a narrow region of bandwidth, as shown by the dotted line (shape of the narrowband filter 304) in the right-hand diagram. The narrow region may be a preset or predefined bandwidth range and can be designed based on the system and / or components. The output of the narrowband filter 304 may exhibit an equalization error shape that is nearly flat and has low peak-to-peak variation in the narrow-bandwidth region. Thus, the equalization error shape of the optical signal generated by the wideband filter 302 and the narrowband filter 304 together in the hybrid gain correction filter may be nearly smooth and flat, as shown in the bottom-left diagram (e.g., the elevated gain equalization error in the lower half of FIG. 2 has already been removed).

[0027] It can be understood that a wideband optical filter can be any type of wideband optical filter having gain correction technology configured to at least correct or equalize the gain shape and its variations over most or all of the transmission bandwidth. A narrowband filter can be understood as any type of narrowband optical filter having gain correction technology configured to at least correct or equalize the gain shape and its variations over a narrow region of the transmission bandwidth. It can also be understood that the hybrid gain correction filter shown in FIG. 3 can be a hybrid GFF located in a repeater or a hybrid GEF located in a separate GEF body, as described in more detail below. Also, various arrangements of filters 302 and 304 of the hybrid filter can be considered, such as placing the narrowband filter 304 first and then the wideband filter 302, or in examples, the hybrid gain correction filter can include two or more filters (e.g., the number and type of filters depending on system design goals, constraints, etc.).

[0028] 4A and 4B illustrate different examples of hybrid gain correction filters 402 and 404 according to embodiments and different technologies that can be implemented therein. As shown in FIG. 4A, for example, hybrid gain correction filter 402 may include at least a wideband GFF and a narrowband GFF, both of which may be based on non-reflective technology (e.g., both the wideband GFF and the narrowband GFF are non-reflective filters), as shown. It can be appreciated that because each stage of hybrid filter 402 employs non-reflective technology, there is no need to place or couple other additional components, such as an isolator, between the stages or after the second stage.

[0029] In another example, as shown in FIG. 4B , the hybrid gain correction filter 404 may further include a wideband GFF and a narrowband GFF. However, the wideband GFF may be based on a reflective technology (e.g., the wideband GFF is a reflective filter), and the narrowband GFF may be based on a reflective or non-reflective technology (e.g., the narrowband GFF may be a reflective or non-reflective filter). Because the wideband GFF of the hybrid gain correction filter 404 is based on a reflective technology, disposing or coupling at least one isolator between the wideband GFF and the narrowband GFF can interpret and substantially cancel any back reflection or interference caused by the reflective characteristics of the wideband GFF. If necessary, additional isolators may be added downstream or upstream of the hybrid filter.

[0030] While GFFs are shown as being used in the hybrid gain correction filters 402 and 404, it is understood that the wideband and narrowband filters of the filters 402 and 404 may be GFFs. Also, as discussed above, the arrangement, order, number, etc. of the filter stages may vary based at least on the system or component design; for example, a reflective wideband GFF of the hybrid filter 404 may be positioned after a narrowband GFF. It is also understood that, to save space and assembly costs, one or more stages of the hybrid filter may be combined into a single package; for example, two or more TFFs may be mounted in a single case, housing, package, etc. It is further understood that the hybrid filter and / or aspects thereof may be chirped or non-chirped; for example, the chirp may be configured to be uniform or variable across the transmission bandwidth.

[0031] Figure 5 illustrates an exemplary hybrid GFF 501 arranged in a repeater according to an embodiment. For example, the repeater, illustrated in the dashed box, may include (e.g., physically house or enclose) multiple EDFAs, such as the single EDFA illustrated in Figure 5. The EDFA may include various internal components such as erbium-doped fiber, isolator(s), tap(s), etc.

[0032] As shown in the figure, the hybrid GFF 501 can be located at and / or coupled to the output of the EDFA in the repeater. As described above, the hybrid GFF 501 includes at least a GFF 502 and a GFF 504, where the GFF 502 can be a wideband GFF and the GFF 504 can be a narrowband GFF. Similar hybrid GFFs can be located at and / or coupled to the outputs of other additional EDFAs in the repeater. As described in more detail below, a hybrid GFF, e.g., the hybrid GFF 501, can be located in each “Nth” repeater, where N is a preset or predefined number selected based at least on the system or component design. Thus, the hybrid GFF 501 can correct or equalize the shape of the gain already accumulated in the N spans. The hybrid GFF 501 may be coupled to the input of an amplifier, placed between stages of a multi-stage amplifier, or placed in an active fiber (e.g., erbium-doped fiber), with or without a pump bypass. Any other arrangement and placement in a wideband amplifier may also be used, for example, a C+L-band EDFA that includes separate C-band and L-band EDFA sections.

[0033] 6 illustrates an exemplary hybrid GEF 601 disposed in a GEF body according to an embodiment. For example, the GEF body may be a separate, independent physical component that includes or houses multiple hybrid GEFs (including the hybrid GEF 601). Thus, the GEF body may be separate from the repeater. It will be appreciated that the number of GEFs disposed or configured in a GEF body may vary and depend on the number of EDFAs in the repeater (e.g., the number of fibers in an optical communication system).

[0034] As shown, similar to the hybrid GFF 501 of FIG. 5, the hybrid GEF 601 may include at least a GFF 602 and a GFF 604, where the GFF 602 may be a wideband GEF and the GFF 604 may be a narrowband GEF. In an example, the GEF body may be coupled to a repeater, such that each hybrid GEF in the GEF body may be coupled or connected to a respective EDFA output of the repeater. At least in this respect, the hybrid GEF in the GEF body operates efficiently similarly to a hybrid GFF, except that the GEFs are at least external to the repeater. Thus, the hybrid GEF and corresponding GEF body enable design flexibility and gain correction in strategic locations in optical communication systems, which is advantageous, particularly in conventional systems with repeaters, as these repeaters are less likely to be configured or modified in the hybrid GFF.

[0035] In addition to the above embodiments and examples, more complex gain correction arrangements are also contemplated. For example, narrowband filters may be configured to correct the gain shape at multiple locations in the optical transmission bandwidth using wideband filters. Also, wideband filters may be designed to cover the entire transmission bandwidth. Various configurations of hybrid gain correction filters are also contemplated. For example, hybrid gain correction may be applied periodically to the repeater itself (e.g., every 12 repeaters) or may be designed to be coupled to individual repeater bodies, as further described below.

[0036] FIG. 7 illustrates an exemplary hybrid GFF implementation 700 in an optical communication system according to an embodiment. For example, FIG. 7 illustrates a unidirectional portion of the optical communication system, the unidirectional portion having at least three separate fibers coupled or connected between a transmitter (Tx) and a receiver (Rx). Repeaters 702, 704, N, N+1, and N+M may be positioned and spaced apart at predetermined distances, intervals, or spans between the transmitter and receiver to amplify the optical signals transmitted on each of the three fibers. As shown in the figure, each repeater (except repeaters N and N+M) may include at least three EDFAs and at least three conventional GFFs, which are coupled to the output points of the EDFAs corresponding to each fiber. Repeaters N and N+M each include at least three EDFAs, but instead of conventional GFFs, three hybrid GFFs may be coupled to the respective EDFA outputs, as shown in the figure. FIG. 7 also illustrates a conventional GEF body 706 (including at least three conventional GEFs) that may be coupled to repeater N+M. It can be understood that typically the minimum number of amplifiers for one transmission direction in a repeater is one or more.

[0037] As described above, the hybrid GFFs of repeaters N and N+M may be configured to correct or equalize any variations or errors in gain shape accumulated across multiple repeater spans. In embodiments, the spacing of the hybrid GFFs may be preset based at least in part on optimal gain correction capabilities and / or system design. For example, the optimal hybrid GFF spacing may be the distance between repeater N and repeater N+M (e.g., after the "Mth" repeater or repeater span M). It will be appreciated that the distance may be greater or less than M.

[0038] 8 illustrates an exemplary hybrid GEF implementation 800 in an optical communication system according to an embodiment. The optical communication system of FIG. 8 may be similar to the system illustrated in FIG. 7 because at least one-way portion of the system has three separate fibers between a transmitter and a receiver, and further includes repeaters 802, 804, N, and N+1, each repeater having three EDFAs and three conventional GFFs corresponding to the corresponding fibers.

[0039] As shown, hybrid GEF body 806 may include at least three hybrid GEFs, and GEF body 806 may be coupled to repeater N to at least correct or equalize accumulated gain shape changes or errors, as described above. Each GEF output in repeater N is coupled to a corresponding hybrid GEF in GEF body 806. One of the many advantages of using hybrid GEFs is that they provide flexibility in installation or configuration, allowing hybrid gain correction filters to be easily integrated into existing system environments, for example, legacy systems that cannot be easily modified.

[0040] FIG. 9 illustrates an exemplary bidirectional hybrid GEF embodiment 900 in an optical communication system according to an embodiment. The optical communication system of FIG. 9 may be similar to the system illustrated in FIG. 8, except that the system is bidirectional. One or more GEF bodies, similar to GEF body 806, having hybrid GEFs may be coupled to one or more repeaters in the system, as shown. Because the communication system is bidirectional, the two GEF bodies illustrated have at least six individual hybrid GEFs, three of which correspond to three fibers in one direction and three of which correspond to three fibers in the opposite direction.

[0041] It can be understood that in some examples, hybrid GFF and hybrid GEF embodiments can both be used in the same communication system to further improve the ability to correct gain equalization errors. For example, a hybrid GFF can be included in each Nth repeater, and a GEF body with a hybrid GEF can be coupled to each Mth repeater, and the rest can be inferred by analogy.

[0042] The multi-stage gain correction filter is advantageous in many ways. As described above, using conventional non-reflective gain correction techniques in repeaters (or conventional GEF bodies) in optical communication systems can be important because it can reduce the total number of passive components (e.g., isolators) in the repeater, ultimately improving the system's power performance and saving various costs associated with the system. Thus, the hybrid gain correction filter (e.g., hybrid GFF, hybrid GEF) corrects any undesirable changes in gain shape (e.g., gain equalization errors) caused by conventional non-reflective gain correction filters in the system. This allows optical communication systems to continue using conventional non-reflective gain correction techniques without the adverse and undesirable effects of gain equalization errors propagating through the system. Additionally, the stages of a hybrid GFF or GEF can be arranged in different ways and implement various techniques (e.g., reflective, non-reflective) therein. In the case of amplifier gain shapes, hybrid GEF(s) or hybrid GFF(s) may be advantageous, where the use of non-hybrid filters (based on reflective or non-reflective techniques) increases gain equalization errors at the receiver site.

[0043] Disclosed herein are novel and innovative techniques for managing gain equalization errors in optical communication systems that use or implement conventional gain correction techniques. The scope of the disclosure is not limited by the particular embodiments described herein. Indeed, in addition to the embodiments and modifications of the disclosure described herein, various other embodiments and modifications of the disclosure will be apparent to those skilled in the art from the foregoing description and drawings.

[0044] Accordingly, such other embodiments and modifications are intended to be included within the scope of the present disclosure. Also, while the present disclosure has been described in the context of particular implementations in particular environments for particular purposes, those skilled in the art will recognize that its usefulness is not limited thereto, and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in accordance with the full breadth and spirit of the present disclosure as described herein. 。 [Item 1] A multi-stage gain correction filter for correcting a gain equalization error, comprising: a first filter; and a second filter different from the first filter, the multi-stage gain correction filter being used in combination with an optical amplifier, the first filter corrects gain equalization errors in a first portion of an optical transmission bandwidth; the second filter corrects gain equalization errors in a second portion of the optical transmission bandwidth; the first portion of the optical transmission bandwidth is wider than the second portion; Multi-stage gain correction filter. [Item 2] the first filter is a wideband gain correction filter; the first portion is most or all of the optical transmission bandwidth; the second filter is a narrowband gain correction filter, and the second portion is a narrow region of the optical transmission bandwidth; Item 1. The multi-stage gain correction filter according to item 1. [Item 3] the multi-stage gain correction filter is disposed in a repeater, and the wideband gain correction filter and the narrowband gain correction filter are gain flattening filters; Item 2. The multi-stage gain correction filter according to item 2. [Item 4] the multi-stage gain correction filter is disposed in an independent body, and the wideband gain correction filter and the narrowband gain correction filter are gain equalization filters; Item 2. The multi-stage gain correction filter according to item 2. [Item 5] the first filter is a reflective filter or a non-reflective filter; When the first filter is the reflective filter, at least one isolator is disposed between the first filter and the second filter. 5. The multi-stage gain correction filter according to any one of items 1 to 4. [Item 6] correcting gain equalization errors in a first portion of the optical transmission bandwidth with a first filter; and correcting the gain equalization error in a second portion of the optical transmission bandwidth with a second filter, the method comprising: The first filter is different from the second filter, the first portion of the optical transmission bandwidth is wider than the second portion; method. [Item 7] the first filter is a wideband gain correction filter; the first portion is most or all of the optical transmission bandwidth; the second filter is a narrowband gain correction filter, and the second portion is a narrow region of the optical transmission bandwidth; The method according to item 6. [Item 8] the multi-stage gain correction filter is disposed in a repeater, and the wideband gain correction filter and the narrowband gain correction filter are gain flattening filters; The method according to item 7. [Item 9] the multi-stage gain correction filter is disposed in an independent body, and the wideband gain correction filter and the narrowband gain correction filter are gain equalization filters; The method according to item 7. [Item 10] the first filter is a reflective filter or a non-reflective filter; When the first filter is the reflective filter, at least one isolator is disposed between the first filter and the second filter. 10. The method according to any one of items 6 to 9. [Item 11] at least one repeater disposed and spaced apart along the fiber optic cable, the repeater including a plurality of erbium-doped fiber amplifiers (EDFAs); a plurality of hybrid gain correction filters; a system in which each of the plurality of hybrid gain correction filters is coupled to an output of a respective EDFA of the at least one repeater, Each hybrid gain correction filter is A first filter; a second filter different from the first filter, the first filter is configured to correct a gain equalization error in a first portion of an optical transmission bandwidth; the second filter is configured to correct a gain equalization error in a second portion of the optical transmission bandwidth; the first portion of the optical transmission bandwidth is wider than the second portion; system. [Item 12] the first filter is a wideband gain correction filter, and the first portion is most or all of the optical transmission bandwidth; the second filter is a narrowband gain correction filter, and the second portion is a narrow region of the optical transmission bandwidth. Item 12. The system according to item 11. [Item 13] the plurality of hybrid gain correction filters are disposed in the at least one repeater, and the wideband gain correction filter and the narrowband gain correction filter are hybrid gain flattening filters; Item 13. The system according to item 12. [Item 14] the plurality of hybrid gain correction filters are disposed in a separate body coupled to the at least one repeater, and the wideband gain correction filter and the narrowband gain correction filter are hybrid gain equalization filters; Item 13. The system according to item 12. [Item 15] the first filter is a reflective filter or a non-reflective filter; When the first filter is the reflective filter, at least one isolator is disposed between the first filter and the second filter. 15. The system according to any one of items 11 to 14.

Claims

1. 1. A hybrid gain correction filter for correcting gain equalization errors, the hybrid gain correction filter comprising: a first filter; and a second filter different from the first filter, the hybrid gain correction filter being used in combination with an optical amplifier, the hybrid gain correction filter comprising: the first filter corrects gain equalization errors in a first portion of an optical transmission bandwidth; the second filter corrects gain equalization errors in a second portion of the optical transmission bandwidth; the first portion of the optical transmission bandwidth is wider than the second portion; The hybrid gain correction filter is tuned to correct for changes in gain shape produced by a gain correction filter coupled to the output of the optical amplifier. Hybrid gain correction filter.

2. the first filter is a wideband gain correction filter; the first portion is most or all of the optical transmission bandwidth; the second filter is a narrowband gain correction filter, and the second portion is a narrow region of the optical transmission bandwidth; 10. The hybrid gain correction filter of claim 1.

3. the hybrid gain correction filter is disposed in a repeater, and the wideband gain correction filter and the narrowband gain correction filter are gain flattening filters; 3. The hybrid gain correction filter of claim 2.

4. the hybrid gain correction filter is disposed in an independent body, and the wideband gain correction filter and the narrowband gain correction filter are gain equalization filters; 3. The hybrid gain correction filter of claim 2.

5. the first filter is a reflective filter or a non-reflective filter; When the first filter is the reflective filter, at least one isolator is disposed between the first filter and the second filter. A hybrid gain correction filter according to any one of claims 1 to 4.

6. correcting a gain equalization error in a first portion of an optical transmission bandwidth for an optical signal with a first filter, the optical signal being output from a gain correction filter coupled to an optical amplifier; and correcting the gain equalization error in a second portion of the optical transmission bandwidth for the optical signal with a second filter, the method comprising: The first filter is different from the second filter, the first portion of the optical transmission bandwidth is wider than the second portion; method.

7. the first filter is a wideband gain correction filter; the first portion is most or all of the optical transmission bandwidth; the second filter is a narrowband gain correction filter, and the second portion is a narrow region of the optical transmission bandwidth; The first filter and the second filter form a hybrid gain correction filter. The method of claim 6.

8. the multi-stage gain correction filter is disposed in a repeater, and the wideband gain correction filter and the narrowband gain correction filter are gain flattening filters; The method of claim 7.

9. the multi-stage gain correction filter is disposed in an independent body, and the wideband gain correction filter and the narrowband gain correction filter are gain equalization filters; The method of claim 7.

10. the first filter is a reflective filter or a non-reflective filter; When the first filter is the reflective filter, at least one isolator is disposed between the first filter and the second filter.

10. The method according to any one of claims 6 to 9.

11. at least one repeater disposed and spaced apart along the optical fiber cable, the repeater including a plurality of erbium-doped fiber amplifiers (EDFAs) and a plurality of gain correction filters respectively coupled to the plurality of EDFAs; a plurality of hybrid gain correction filters tuned to correct for variations in gain shape produced by the plurality of gain correction filters; a system in which each of the plurality of hybrid gain correction filters is coupled to an output of each EDFA of the at least one repeater by one gain correction filter of the plurality of gain correction filters, Each hybrid gain correction filter is A first filter; a second filter different from the first filter, the first filter corrects gain equalization errors in a first portion of an optical transmission bandwidth; the second filter corrects gain equalization errors in a second portion of the optical transmission bandwidth; the first portion of the optical transmission bandwidth is wider than the second portion; system.

12. the first filter is a wideband gain correction filter, and the first portion is most or all of the optical transmission bandwidth; the second filter is a narrowband gain correction filter, and the second portion is a narrow region of the optical transmission bandwidth. The system of claim 11.

13. the plurality of hybrid gain correction filters are disposed in the at least one repeater, and the wideband gain correction filter and the narrowband gain correction filter are hybrid gain flattening filters; The system of claim 12.

14. the plurality of hybrid gain correction filters are disposed in separate bodies coupled to the at least one repeater, and the wideband gain correction filter and the narrowband gain correction filter are hybrid gain equalization filters; The system of claim 12.

15. the first filter is a reflective filter or a non-reflective filter; When the first filter is the reflective filter, at least one isolator is disposed between the first filter and the second filter.

15. A system according to any one of claims 11 to 14.

16. A multi-stage gain correction filter for correcting gain equalization errors, comprising a first filter and a second filter different from the first filter, and used in combination with an optical amplifier, the first filter corrects gain equalization errors in a first portion of an optical transmission bandwidth; the second filter corrects gain equalization errors in a second portion of the optical transmission bandwidth; the first portion of the optical transmission bandwidth is wider than the second portion; the first filter is a reflective filter or a non-reflective filter; When the first filter is the reflective filter, at least one isolator is disposed between the first filter and the second filter. Multi-stage gain correction filter.

17. A multi-stage gain compensation filter coupled to an optical amplifier disposed in one or more optical transmission paths of an optical communication system configured to transmit a signal via the one or more optical transmission paths, comprising: each of the one or more optical communication paths includes one or more spans; The multi-stage gain correction filter is A first filter; a second filter different from the first filter, the first filter corrects gain equalization errors in a first portion of an optical transmission bandwidth; the second filter corrects gain equalization errors in a second portion of the optical transmission bandwidth; the first portion of the optical transmission bandwidth is wider than the second portion; The first filter and the second filter correct or equalize a gain shape of a signal gain accumulated over a plurality of spans preceding the first filter and the second filter in the one or more optical communication paths. Multi-stage gain correction filter.

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