Erbium-doped fiber amplifier with multiple pump lasers

Abstract

The invention relates to an erbium-doped fiber amplifier with multiple pump lasers. A method of amplification in an optical fiber includes injecting a first set of pump laser light of one or more wavelengths into the optical fiber between an input and an output of the optical fiber by one or more pump lasers; and injecting a second set of pump laser light of one or more wavelengths into the optical fiber between the input and output of the optical fiber by the one or more pump lasers. The wavelengths of the pump lasers injected into the first and second sets of the optical fiber differ from each other in a range between 968 nm and 982 nm or between 1470 nm and 1490 nm and cause inversion in the optical fiber, and the wavelengths of the pump lasers injected into the first and second sets of the optical fiber differ from the laser at the one or more communication wavelengths.

Description

Technical Field

[0001] The present disclosure relates to systems and methods for providing or generating inversion in an erbium-doped fiber amplifier (EDFA). Background Art

[0002] An erbium-doped fiber amplifier (EDFA) is an optical pump amplifier in which a higher energy pump laser is used to generate inversion within an energy band, resulting in stimulated signal amplification. Conventional pump lasers operate at wavelengths of approximately 980 nm and approximately 1480 nm.

[0003] EDFAs are used in optical transmission systems to amplify a single signal channel or multiple signal channels simultaneously. Importantly, all signal channels see the same gain through any EDFA to ensure that the signal channels reach one or more receivers within an allowable input power range.

[0004] In an EDFA, there are several reasons that result in non-equal amplification of all signal channels. One reason is related to the optical pump lasers used to provide inversion for the gain process in the C-band or L-band. Specifically, 980 nm laser pumps are more commonly used in EDFAs than 1480 nm due to better noise performance, lower power dissipation, and more compact modules. However, the 980 nm pump laser can be the cause of gain variations across all signal channels through a process called pump-induced gain inhomogeneity (PIGI).

[0005] To this end, the 980 nm pump laser chip is a Fabry-Perot structure that will shift the center wavelength as the operating temperature and drive current are changed. As the center wavelength shifts, this creates non-uniform gain variations across all signal channels passing through the EDFA. This results in significant gain variations for some signal channels and slight variations for other signal channels. For example, when the center wavelength of the pump laser chip is offset, the gain variation of the short wavelength channels can be much greater than that of the long wavelength channels.

[0006] Therefore, the Fabry-Perot 980 nm pump laser chip is designed to have a locking reflector, typically a fiber Bragg grating (FBG), which ensures that the laser wavelength is fixed under its operating conditions, minimizing gain variations in the EDFA.

[0007] The pump laser can be injected into the EDFA, either co-propagating in the same direction as the propagation direction of the signal channels or counter-propagating in the opposite direction to the propagation direction of the signal channels. Co-propagation provides lower noise performance. Counter-propagation provides higher output power.

[0008] Both co-propagating and counter-propagating injection can reduce noise in an EDFA and increase output power. However, injecting into the same EDF loop causes light from a pump laser in one direction to not be fully absorbed by the EDF and be coupled into the opposing pump laser. This creates instability in the opposing pump laser, which in turn creates an undesirable unstable gain in the EDFA. This is especially a problem for lasers nominally frequency locked to the same wavelength due to the proximity of the locked wavelengths.

[0009] Accordingly, a solution is needed to minimize PIGI and prevent gain instability in co-propagating and counter-propagating 980 nm pumped EDFAs. SUMMARY OF THE INVENTION

[0010] Disclosed is a method of amplifying in an optical fiber having an input for receiving laser light of one or more communication wavelengths from one or more laser transmitters and an output for outputting the laser light of the one or more communication wavelengths to one or more laser receivers. The method includes: (a) injecting, via one or more pump lasers, a first set of one or more wavelengths of pump laser light into the optical fiber between the input and output of the optical fiber; and (b) injecting, via the one or more pump lasers, a second set of one or more wavelengths of pump laser light into the optical fiber between the input and output of the optical fiber, wherein: the wavelengths of the first and second sets of pump laser light injected into the optical fiber are different from each other within a range between 968 nm and 982 nm or between 1470 nm and 1490 nm and create inversion in the optical fiber, and the wavelengths of the first and second sets of pump laser light injected into the optical fiber are different from the laser light of the one or more communication wavelengths.

[0011] The first set of one or more wavelengths of pump laser light and the second set of one or more wavelengths of pump laser light may be injected into the optical fiber in the same direction towards the output of the optical fiber or towards the input of the optical fiber.

[0012] The first set of one or more wavelengths of pump laser light and the second set of one or more wavelengths of pump laser light may be injected into the optical fiber in different directions.

[0013] Injecting the first and second sets of one or more wavelengths of pump laser light into the optical fiber may create gain in the laser light of the one or more communication wavelengths.

[0014] The pump laser of one or more wavelengths of the first group may include one or more of the following wavelengths: 970nm ± 1.0nm, 972nm ± 1.0nm, 974nm ± 1.0nm, 976nm ± 1.0nm, 978nm ± 1.0nm, and the pump laser of one or more wavelengths of the second group may include one or more of the following wavelengths: 970nm ± 1.0nm, 972nm ± 1.0nm, 974nm ± 1.0nm, 976nm ± 1.0nm, 978nm ± 1.0nm.

[0015] The pump laser of one or more wavelengths of the first group may include wavelengths of 974nm ± 1.0nm and 974nm ± 1.0nm. The pump laser of one or more wavelengths of the second group may include wavelengths of 972nm ± 1.0nm and 978nm ± 1.0nm or 976nm ± 1.0nm and 978nm ± 1.0nm.

[0016] The wavelengths of the first group and the wavelengths of the second group may be injected into the optical fiber via one or more combiners or multiplexers. Description of the Drawings

[0017] Figure 1A is a schematic diagram of an example of a wavelength division multiplexing (WDM) system according to the principles of the present disclosure;

[0018] Figure 1B - Figure 1C is a schematic diagram of different configurations of an optical amplifier according to the principles of the present disclosure, which can be used with Figure 1A the example WDM disclosed in;

[0019] Figure 2A - Figure 2D is a schematic diagram of different configurations of a pump laser according to the principles of the present disclosure, which can be used with each example amplifier shown in Figure 1B - Figure 1C ; and

[0020] Figure 3 is a flowchart of a method according to the principles of the present disclosure. Detailed Description

[0021] As used herein, spatial or directional terms such as "left", "right", "inner", "outer", "above", "below", etc. relate to the disclosure as shown in the drawings. However, it should be understood that the present disclosure may take various alternative orientations, and thus, these terms should not be considered restrictive. In addition, as used herein, all numbers representing dimensions, physical properties, processing parameters, amounts of ingredients, reaction conditions, etc. used in the specification and claims should be understood to be modified in all cases by the term "about" or "approximately". Therefore, unless otherwise indicated, the numerical values set forth in the following specification and claims may vary depending on the desired properties sought to be obtained by the present disclosure.

[0022] At a minimum, and without attempting to limit the application of the doctrine of equivalents in the scope of the claims, each numerical value should be construed at least in accordance with the numerical value of the reported significant digits and by application of ordinary rounding techniques. Additionally, all ranges disclosed herein should be understood to include the starting and ending range values, and any and all sub-ranges subsumed therein. For example, the recited range "1 to 10" should be considered to include any and all sub-ranges between the minimum value 1 and the maximum value 10 (and including the end values); that is, all sub-ranges starting with the minimum value 1 or greater and ending with the maximum value 10 or less, such as 1 to 3.3, 4.7 to 7.5, 5.5 to 10, etc. "A" or "an" means one or more.

[0023] As used herein, "coupled," "coupled to," and like terms refer to two or more elements that are joined, linked, fastened, connected, in communication, or otherwise associated with each other (e.g., mechanically, electrically, fluidically, optically, electromagnetically). In various examples, the elements can be associated directly or indirectly. As an example, element A can be directly associated with element B. As another example, element A can be indirectly associated with element B via, for example, another element C. It will be understood that not all of the association relationships between the various disclosed elements are necessarily presented. Thus, there can also be couplings other than those shown in the figures.

[0024] As used herein, the phrase "at least one," when used in conjunction with a list of items, means that different combinations of one or more of the listed items can be used, and only one of each item in the list may be required. For example, "at least one of item A, item B, and item C" can include, but is not limited to, item A or item A and item B. This example can also include item A, item B, and item C, or item B and item C. In other examples, "at least one" can be, for example but not limited to, two of item A, one of item B, and ten of item C; four of item B and seven of item C; and other suitable combinations.

[0025] Embodiments will now be described in connection with providing or generating inversion in an erbium-doped fiber amplifier (EDFA). However, this should not be construed as limiting, as it is conceivable that in each instance, the EDFA could be replaced with a fiber amplifier doped with bismuth, praseodymium, or neodymium.

[0026] Various non-limiting examples will now be described with reference to the accompanying drawings, in which like reference numerals and their basic symbols (e.g., 28 and 28') correspond to like or functionally equivalent elements.

[0027] Reference Figure 1A, an exemplary wavelength division multiplexing (WDM) system 2 according to the principles of the present disclosure may include a transmission optical fiber 4, one or more optical amplifiers 6 (e.g., optical amplifiers 6-1 and / or 6-2) for optically amplifying the optical signals or lasers propagating in the transmission optical fiber 4, one or more laser transmitters 8-1, …, 8-n coupled to the input end 10 of the transmission optical fiber 4 via a WDM multiplexer 12, and one or more laser receivers 14-1, …, 14-n coupled to the output end 16 of the transmission optical fiber 4 via a WDM demultiplexer 18. In one example, the transmission optical fiber 4 may be implemented by a large number of continuously connected segments of transmission optical fiber. In one example, the transmission optical fiber 4 or each of its segments may be manufactured by Corning Incorporated of Corning, New York, USA optical fiber. and are registered trademarks of Corning Incorporated of Corning, New York, USA.

[0028] One or more laser transmitters 8-1, …, 8-n may be configured and / or operated to generate lasers of one or more communication wavelengths λ1, …, λn, which are multiplexed together by the WDM multiplexer 12 and input into the input end 10 of the transmission optical fiber 4. The lasers of the one or more multiplexed communication wavelengths λ1, …, λn received at the input end 10 of the transmission optical fiber 4 propagate through one or more optical amplifiers 6 to the output end 16 of the transmission optical fiber 4, where the lasers of the one or more multiplexed communication wavelengths λ1, …, λn are amplified, and at the output end, the lasers of the multiplexed communication wavelengths λ1, …, λn are demultiplexed by the demultiplexer 18 and provided to one or more laser receivers 14-1, …, 14-n.

[0029] In a non-limiting example where the variable “n” = 3, the laser transmitter 8-1 and the laser receiver 12-1 may be configured to respectively transmit and receive a communication wavelength λ1 in a first laser band, the first laser band being in one of the C band, L band, S band, O band, E band, or U band; the laser transmitter 8-2 and the laser receiver 12-2 may be configured to respectively transmit and receive a communication wavelength λ2 in a second laser band different from the first laser band, the second laser band being in a different one of the C band, L band, S band, O band, E band, or U band; and the laser transmitter 8-3 and the laser receiver 12 may be configured to respectively transmit and receive a communication wavelength λ3 in a third laser band different from the first and second laser bands. However, this example should not be construed as limiting, since the variable “n” may be equal to 1 or more.

[0030] In fact, each laser band may include multiple channels or wavelengths of the laser, such as 96 or more channels or wavelengths, and some channels or wavelengths may be present in more than one band. For the purpose of simplicity and not limitation, the present disclosure will be described in connection with lasers of communication channels or wavelengths λ1, …, λn (such as lasers of communication wavelengths λ1, λ2, and λ3).

[0031] In one example, each of the one or more lasers of communication wavelengths λ1, …, λn may include one or more wavelengths of laser in one or more of the C band, L band, S band, O band, E band, and U band. In one example, the C band may have a wavelength range between approximately 1525 nm and 1565 nm; the L band may have a wavelength range between approximately 1565 nm and 1625 nm; the S band may have a wavelength range between approximately 1460 nm and 1530 nm; the O band may have a wavelength range between approximately 1260 nm and 1360 nm; the E band may have a wavelength range between approximately 1360 nm and 1460 nm; the U band may have a wavelength range between approximately 1675 nm and 1700 nm.

[0032] Example 1:

[0033] Reference Figure 1B And continuing to refer Figure 1A , in a non-limiting example or aspect, the WDM system 2 may include one or more instances of the optical amplifier 6-1 along the length of the transmission fiber 4, that is, one or more instances of the optical amplifier 6-2 shown in Figure 1A may be omitted. For simplicity, hereinafter, although only one instance of the optical amplifier 6-1 shown in Figure 1A will be described, it should be understood that the description of the optical amplifier 6-1 may apply to any other instance of the optical amplifier 6-1 that may be distributed along the length of the transmission fiber 4.

[0034] Optical amplifier 6-1 may include an optional input optical isolator 20-1 and an optional output optical isolator 20-2. The input end of the input optical isolator is (directly or indirectly) coupled to the input end 10 of the transmission optical fiber 4, and the output of the output optical isolator is (directly or indirectly) coupled to the output end 16 of the transmission optical fiber 4. Optical amplifier 6-1 may also include a section of erbium-doped fiber (EDF) 22, whose input end is connected to the output end of the input optical isolator 20-1, and the output end is connected to the input end of the output optical isolator 202. The examples described in this disclosure will relate to EDF 22. However, this should not be construed as restrictive, as it is conceivable that EDF 22 can be replaced with a fiber doped with bismuth, praseodymium, thulium, ytterbium, holmium, dysprosium, neodymium, or a combination of erbium / ytterbium and used with an injection pump laser having a wavelength different from the wavelengths described in this disclosure.

[0035] Optical amplifier 6-1 may include a first pump laser 24-1, which may be coupled, for example, via a combiner or multiplexer 26-1 to the EDF 22 closer to the input optical isolator 20-1. Optical amplifier 6-1 may also include a second pump laser 24-2, which may be coupled, for example, via a combiner or multiplexer 26-2 to the EDF 22 closer to the output optical isolator 20-2. Depending on the number of wavelengths of pump laser to be injected into the EDF 22, optical amplifier 6-1 may include one, two, or more pump lasers 24, as may be considered suitable and / or desirable for the application.

[0036] In one example, the first and second pump lasers 24-1 and 24-2 of optical amplifier 6-1 may be operable or configured to inject pump laser 28 of one or more wavelengths of a first group and pump laser 30 of one or more wavelengths of a second group into the EDF 22 via combiners 26-1 and 26-2. In one example, the wavelengths of the pump lasers 28 and 30 of the first and second groups injected into the EDF 22 of optical amplifier 6-1 may be different from each other, and the wavelengths of the pump lasers 28 and 30 of the first and second groups injected into the EDF 22 of optical amplifier 6-1 may also be different from the laser of one or more communication wavelengths λ1,..., λn propagating on the EDF 22 through optical amplifier 6-1.

[0037] In one example, the pump laser 28 of one or more wavelengths of the first group injected into the EDF 22 of the optical amplifier 6-1 may include one or more wavelengths within the wavelength range between 968 nm and 982 nm. In one example, the pump laser 28 of one or more wavelengths of the first group injected into the EDF 22 of the optical amplifier 6-1 may include one or more of the following wavelengths: 970 nm ± 0.5 nm, 972 nm ± 0.5 nm, 974 nm ± 0.5 nm, 976 nm ± 0.5 nm, 978 nm ± 0.5 nm. In one example, the pump laser 30 of one or more wavelengths of the second group injected into the EDF 22 of the optical amplifier 6-1 may also include one or more wavelengths within the wavelength range between 968 nm and 982 nm. In one example, the pump laser 30 of one or more wavelengths of the second group injected into the EDF 22 of the optical amplifier 6-1 may include one or more of the following wavelengths: 970 nm ± 0.5 nm, 972 nm ± 0.5 nm, 974 nm ± 0.5 nm, 976 nm ± 0.5 nm, 978 nm ± 0.5 nm. However, as described above, the wavelengths of the pump lasers 28 and 30 of the first and second groups injected into the EDF 22 of the optical amplifier 6-1 may be different from each other. In one example, the pump laser 28 of one or more wavelengths of the first group may include a single wavelength, and the pump laser 30 of one or more wavelengths of the second group may include a different single wavelength. However, this should not be construed as limiting. In addition, although the wavelength of each of the pump lasers 28 and 30 of the first and second groups may be described as varying by ±0.5 nm, this should not be construed as limiting, because it is contemplated that throughout the present disclosure, each of the one or more wavelengths may vary by up to ±1.0 nm.

[0038] In Figure 1B In the illustrated example amplifier 6-1, the pump lasers 28 and 30 of one or more wavelengths of the first and second groups may be injected into the EDF 22 via combiners 26-1 and 26-2 toward the output end 16 of the transmission fiber 4, i.e., co-propagate in the same direction as the propagation direction of the laser of one or more multiplexed communication wavelengths λ1, …, λn. The injection directions of the pump lasers 28 and 30 of one or more wavelengths toward the output end 16 of the transmission fiber 4 are Figure 1B shown by arrows 32-1 and 32-2 in

[0039] Example 2:

[0040] Referring Figure 1C and continuing to refer Figure 1A to, in another non-limiting example or aspect, the WDM 2 may include one or more instances of the optical amplifier 6-2 along the length of the transmission fiber 4, i.e.,Figure 1A One or more instances of the optical amplifier 6-1 shown in Figure 1A . For simplicity, in the following, although only one instance of the optical amplifier 6-2 shown in FIG. 1 will be described, it should be understood that such a description of the optical amplifier 6-2 can be applied to any other instance of the optical amplifier 6-2 that may be distributed along the length of the transmission optical fiber 4.

[0041] Except for the following differences, the optical amplifier 6-2 can be similar to the above-described optical amplifier 6-1, that is, the pump lasers 28' and 30' of one or more wavelengths of the first group and the second group can be injected into the EDF 22 of the optical amplifier 6-2 by the first and second pump lasers 24-1' and 24-2' of the optical amplifier 6-2 through the combiners 26-1' and 26-2' toward the input end 10 of the transmission optical fiber 4, that is, in a direction opposite to the propagation direction of the laser of one or more multiplexed communication wavelengths λ1,..., λn. The injection directions of the pump lasers 28' and 30' of one or more wavelengths toward the input end 16 of the transmission optical fiber 4 are shown by the arrows 32-1' and 32-2' in Figure 1C . Figure 1C Shown by the arrows 32-1' and 32-2' in Figure 1C .

[0042] In one example, the first and second pump lasers 24-1' and 24-2' of the optical amplifier 6-2 are operable or configured to inject the pump laser 28' of one or more wavelengths of the first group and the pump laser 30' of one or more wavelengths of the second group into the EDF 22 through the combiners 26-1' and 26-2'. In one example, the wavelengths of the pump lasers 28' and 30' of the first group and the second group injected into the EDF 22 can be different from each other, and the wavelengths of the pump lasers 28' and 30' of the first group and the second group injected into the EDF 22 can also be different from the laser of one or more communication wavelengths λ1,..., λn propagating through the optical amplifier 6-1 on the EDF 22. In one example, the pump laser 28' of one or more wavelengths of the first group can include a single wavelength, and the pump laser 30' of one or more wavelengths of the second group can include different single wavelengths. However, this should not be construed as restrictive.

[0043] In one example, the pump laser 28' of one or more wavelengths of the first group injected into the EDF 22 of the optical amplifier 6-2 may include one or more wavelengths within the wavelength range between 968 nm and 982 nm. In one example, the pump laser 28' of one or more wavelengths of the first group injected into the EDF 22 of the optical amplifier 6-2 may include one or more of the following wavelengths: 970 nm ± 0.5 nm, 972 nm ± 0.5 nm, 974 nm ± 0.5 nm, 976 nm ± 0.5 nm, 978 nm ± 0.5 nm. In one example, the pump laser 30' of one or more wavelengths of the second group injected into the EDF 22 of the optical amplifier 6-2 may include one or more wavelengths within the wavelength range between 968 nm and 982 nm. In one example, the pump laser 30' of one or more wavelengths of the second group injected into the EDF 22 of the optical amplifier 6-2 may include one or more of the following wavelengths: 970 nm ± 0.5 nm, 972 nm ± 0.5 nm, 974 nm ± 0.5 nm, 976 nm ± 0.5 nm, 978 nm ± 0.5 nm. However, as described above, the wavelengths of the pump lasers 28' and 30' of the first and second groups injected into the EDF 22 of the optical amplifier 6-2 may be different from each other. In addition, although the wavelength of each of the pump lasers 28' and 30' of the first and second groups may be described as varying by ±0.5 nm, this should not be construed as limiting, as it is contemplated that throughout the present disclosure, each of the one or more wavelengths may vary by up to ±1.0 nm.

[0044] Reference Figure 1A to the example WDM 2 system shown in Figure 1B and Figure 1C the optical amplifiers 6-1 and 6-2 shown in Figure 1B In a particular non-limiting example, one or more of the C-band, L-band, S-band, O-band, E-band, and / or U-band of the communication wavelengths or the laser of one or more communication wavelengths λ1,..., λn may be input by one or more laser transmitters 8-1,..., 8-n to the input end 10 of the transmission fiber 4 to propagate to the output end 16 of the transmission fiber 4 for reception by one or more laser receivers 12-1,..., 12-n. At the same time, one or more pump laser wavelengths of the first group and one or more pump laser wavelengths of the second group may be injected into the EDF 22: (1) towards the output end 16 of the transmission fiber 4 ( Figure 1B ), so that the injected pump lasers 28 and 30 propagate in the same direction as one or more bands of the laser of the communication wavelengths λ1,..., λn; or (2) towards the input end 10 of the transmission fiber 4 ( Figure 1C), so that the injected pump lasers 28' and 30' counter-propagate in a direction opposite to the propagation direction of one or more bands of the lasers at the communication wavelengths λ1, …, λn.

[0045] In one particular non-limiting example, the pump laser 28 or 28' of one or more wavelengths of the first set may include a single wavelength of 974 nm ± 0.5 nm, and the pump laser 30 or 30' of one or more wavelengths of the second set may include a single wavelength of 976 nm ± 0.5 nm. However, this should not be construed as limiting, as it is contemplated that each of the pump lasers (28 and 30 or 28' and 30') of one or more wavelengths of the first and second sets injected into the EDF 22 may include any one or more of the following wavelengths: 970 nm ± 0.5 nm, 972 nm ± 0.5 nm, 974 nm ± 0.5 nm, 976 nm ± 0.5 nm, and 978 nm ± 0.5 nm, provided that the pump lasers 28 and 30 or 28' and 30' of one or more wavelengths of the first and second sets do not have a common wavelength, i.e., the pump lasers 28 and 30 or 28' and 30' of one or more wavelengths of the first and second sets are mutually exclusive or non-overlapping.

[0046] It has been observed that when two or more different wavelengths of the pump lasers of the above wavelengths are injected in the same direction or in the counter-propagation direction as the above bands of the lasers at the communication wavelengths λ1, …, λn, inversion is generated or caused in the EDF 22, which helps to achieve higher gain and / or output power in the bands of the lasers at the communication wavelengths λ1, …, λn propagating in the transmission fiber 4.

[0047] Reference Figure 2A - Figure 2D , in one example, the pump lasers 28 and 30 and / or 28' and 30' of one or more wavelengths of the first and second sets may be generated from both sides of a single pump laser chip 36 including the pump laser 6 ( Figure 2A ), or from two outputs on one side of a single laser chip 36 including the pump laser 6 ( Figure 2B ), or from two laser chips 36 and 36' including the pump laser 6 ( Figure 2C ), generated from one side of a single pump laser 6 ( Figure 2D ).

[0048] Example 3:

[0049] Continuing to refer to Figure 1A - Figure 1C , in another example, the WDM 2 may include one or more pairs of optical amplifiers 6-1 and 6-2. For the purposes of the present disclosure, only one pair of optical amplifiers 6-1 and 6-2 will be described ( Figure 1A(shown in). However, this should not be construed as restrictive. In this example, the pump lasers (28 and 30) of one or more wavelengths in the first group and the pump lasers (28' and 30') of one or more wavelengths in the second group can be simultaneously injected into the respective EDFs 22 of the optical amplifiers 6-1 and 6-2 via the pump lasers 24-1 and 24-2 (for pump lasers 28 and 30) of the optical amplifier 6-1 and the pump lasers 24-1' and 24-2' (for pump lasers 28' and 30') of the optical amplifier 6-2, towards the respective output end 16 and input end 10 of the transmission fiber 4. In this example, the pump lasers 28 and 30 of one or more wavelengths in the first group co-propagate in the same direction as the propagation direction of the lasers of one or more multiplexed communication wavelengths λ1, …, λn, while the pump lasers 28' and 30' of one or more wavelengths in the second group counter-propagate in the direction opposite to the propagation direction of the lasers of one or more multiplexed communication wavelengths λ1, …, λn.

[0050] In this example (similar to the above example), the pump lasers 28 and 30 of one or more wavelengths in the first group injected into the EDF 22 of the optical amplifier 6-1 can include one or more wavelengths within the wavelength range between 968 nm and 982 nm. In one example, the pump lasers 28 and 30 of one or more wavelengths in the first group injected into the EDF 22 of the optical amplifier 6-1 can include one or more of the following wavelengths: 970 nm ± 0.5 nm, 972 nm ± 0.5 nm, 974 nm ± 0.5 nm, 976 nm ± 0.5 nm, 978 nm ± 0.5 nm. In one example, the pump lasers 28' and 30' of one or more wavelengths in the second group injected into the EDF 22 of the optical amplifier 6-2 can include one or more wavelengths within the wavelength range between 968 nm and 982 nm. In one example, the pump lasers 28' and 30' of one or more wavelengths in the second group injected into the EDF 22 of the optical amplifier 6-2 can include one or more of the following wavelengths: 970 nm ± 0.5 nm, 972 nm ± 0.5 nm, 974 nm ± 0.5 nm, 976 nm ± 0.5 nm, 978 nm ± 0.5 nm. However, as described above, the wavelengths of the pump lasers 28 and 30 of one or more wavelengths in the first group and the pump lasers 28' and 30' of one or more wavelengths in the second group injected into the EDFs 22 of the optical amplifiers 6-1 and 6-2 can be different from each other. In addition, although the wavelength of each of the pump lasers (28 and 30) of one or more wavelengths in the first group and the pump lasers (28' and 30') of one or more wavelengths in the second group can be described as varying by ±0.5 nm, this should not be construed as restrictive, because it can be envisioned that throughout the present disclosure, each of these one or more wavelengths can vary by up to ±1.0 nm.

[0051] In a non - limiting example, the pump lasers 28 and / or 30 of one or more wavelengths of the first group may include a single wavelength of 974 nm ± 0.5 nm injected into the EDF 22 by at least one of the pump lasers 24 - 1 and 24 - 2, and the pump lasers 28' and / or 30' of one or more wavelengths of the second group may include a single wavelength of 976 nm ± 0.5 nm injected into the EDF 22 by at least one of the pump lasers 24 - 1' and 24 - 2'.

[0052] In another non - limiting example, the pump lasers 24 of one or more wavelengths of the first group may include wavelengths of 974 nm ± 0.5 nm and 976 nm ± 0.5 nm injected by the respective pump lasers 24 - 1 and 24 - 2, while the pump lasers 24 of one or more wavelengths of the second group may include wavelengths of 972 nm ± 0.5 nm (or 976 nm ± 0.5 nm) and 978 nm ± 0.5 nm injected by the respective pump lasers 24 - 1' and 24 - 2'.

[0053] It has been observed that when two or more different wavelengths of the pump laser of the above - mentioned wavelengths are simultaneously injected in the same common propagation direction and the opposite propagation direction as the above - mentioned wavelength band of the lasers of the communication wavelengths λ1, …, λn, inversion is generated or caused in the EDF 22 of the optical amplifiers 6 - 1 and 6 - 2, which helps to achieve higher gain and / or output power in the wavelength band of the lasers of the communication wavelengths λ1, …, λn propagating in the transmission fiber 4.

[0054] In the present disclosure, the number of pump lasers of each optical amplifier can be selected based on the number of wavelengths of the pump laser to be injected by the optical amplifier. For example, if an optical amplifier is to be used to inject a pump laser of one wavelength, the optical amplifier may include only one pump laser. In another example, if an optical amplifier is to be used to inject pump lasers of multiple wavelengths, the optical amplifier may include a similar number of pump lasers. Therefore, the illustration of the optical amplifier 6 - 1 including the pump lasers 24 - 1 and 24 - 2 and the optical amplifier 6 - 2 including the pump lasers 24 - 1' and 24 - 2' should not be construed as restrictive.

[0055] Although the foregoing Examples 1-3 have been described in connection with pump lasers within the wavelength range between 968 nm and 982 nm, this should not be construed as restrictive, as it is contemplated that each wavelength range between 968 nm and 982 nm can be replaced by a wavelength range between 1470 nm and 1490 nm. For example, the pump lasers 28 and 30 of one or more wavelengths in the first group injected into the EDF 22 of the optical amplifier 6-1 can include one or more of the following wavelengths: 1472 nm ± 0.5 nm, 1474 nm ± 0.5 nm, 1476 nm ± 0.5 nm, 1478 nm ± 0.5 nm, 1480 nm ± 0.5 nm, 1482 nm ± 0.5 nm, 1484 nm ± 0.5 nm, 1486 nm ± 0.5 nm, and 1488 nm ± 0.5 nm. In this example, the pump lasers 28' and 30' of one or more wavelengths in the second group injected into the EDF 22 of the optical amplifier 6-2 can include one or more of the following wavelengths: 1472 nm ± 0.5 nm, 1474 nm ± 0.5 nm, 1476 nm ± 0.5 nm, 1478 nm ± 0.5 nm, 1480 nm ± 0.5 nm, 1482 nm ± 0.5 nm, 1484 nm ± 0.5 nm, 1486 nm ± 0.5 nm, and 1488 nm ± 0.5 nm. Although each of the wavelengths of the one or more pump lasers (28 and 30) in the first group within the wavelength range between 1470 nm and 1490 nm and the wavelengths of the one or more pump lasers (28' and 30') in the second group within the wavelength range between 1470 nm and 1490 nm can be described as varying by ±0.5 nm, this should not be construed as restrictive, as each of these one or more wavelengths can vary by up to ±1.0 nm.

[0056] It should be understood that in the examples described in the present disclosure, the injected pump lasers of one or more wavelengths in the first and second groups within the wavelength range between 968 nm and 982 nm or between 1470 nm and 1490 nm can be selected to be potentially suitable and / or desirable for creating or causing inversion in the EDF 22, which helps to achieve higher gain and / or output power in the wavelength bands of the lasers of the communication wavelengths λ1,..., λn propagating in the transmission fiber 4. For example, the wavelength of each of the injected pump lasers of one or more wavelengths in the first and second groups can include one or more even wavelengths (e.g., 970 nm or 1472 nm), or one or fewer odd wavelengths (e.g., 971 nm or 1473 nm), or one or more fractional wavelengths (e.g., 971.5 nm or 1472.3 nm), or some combination thereof. Therefore, the specific examples of the wavelengths of the injected pump lasers of one or more wavelengths in the first and second groups described in the above examples should not be construed as restrictive.

[0057] Reference Figure 3 Figure 3 Continuing to refer to all of the foregoing figures, a method of amplifying in an optical fiber having an input end for receiving laser light of one or more communication wavelengths from one or more laser transmitters and an output end for outputting the laser light of the one or more communication wavelengths to one or more laser receivers, the method may include step S1, in which pump laser light of one or more wavelengths of a first group is injected into the optical fiber between the input end and the output end of the optical fiber by one or more pump lasers in a co-propagating or counter-propagating direction as the laser light of the one or more communication wavelengths. In step S2, pump laser light of one or more wavelengths of a second group is injected into the optical fiber between the input end and the output end of the optical fiber by the one or more pump lasers in a co-propagating or counter-propagating direction as the laser light of the one or more communication wavelengths.

[0058] In the method, the wavelengths of the pump laser light of the first and second groups injected into the optical fiber may be different from each other in the range between 968 nm and 982 nm or between 1470 nm and 1490 nm, and create inversion in the optical fiber, and the wavelengths of the pump laser light of the first and second groups injected into the optical fiber may be different from the laser light of the one or more communication wavelengths.

[0059] The pump laser light of one or more wavelengths of the first group and the pump laser light of one or more wavelengths of the second group may be injected into the optical fiber in the same direction toward the output end of the optical fiber, or may be injected into the optical fiber in the same direction toward the input end of the optical fiber, or may be injected into the optical fiber in different directions.

[0060] Other non-limiting examples or aspects of the present disclosure are set forth in the following illustrative and exemplary numbered clauses:

[0061] Clause 1: A method of amplifying in an optical fiber having an input end for receiving laser light of one or more communication wavelengths from one or more laser transmitters and an output end for outputting the laser light of the one or more communication wavelengths to one or more laser receivers, the method comprising: (a) injecting pump laser light of one or more wavelengths of a first group into the optical fiber between the input end and the output end of the optical fiber by one or more pump lasers; and (b) injecting pump laser light of one or more wavelengths of a second group into the optical fiber between the input end and the output end of the optical fiber by the one or more pump lasers. Wherein the wavelengths of the pump laser light of the first and second groups injected into the optical fiber are different from each other in the range between 968 nm and 982 nm or between 1470 nm and 1490 nm, and create or cause inversion in the optical fiber, and the wavelengths of the pump laser light of the first and second groups injected into the optical fiber are different from the laser light of the one or more communication wavelengths.

[0062] Clause 2: The method according to Clause 1, wherein the pump laser of one or more wavelengths of the first group and the pump laser of one or more wavelengths of the second group can be injected into the optical fiber in the same direction towards the output end of the optical fiber.

[0063] Clause 3: The method according to Clause 1 or 2, wherein the pump laser of one or more wavelengths of the first group and the pump laser of one or more wavelengths of the second group can be injected into the optical fiber in the same direction towards the input end of the optical fiber.

[0064] Clause 4: The method according to any one of Clauses 1 to 3, wherein the pump laser of one or more wavelengths of the first group and the pump laser of one or more wavelengths of the second group can be injected into the optical fiber in different directions.

[0065] Clause 5: The method according to any one of Clauses 1 to 4, wherein the pump laser of one or more wavelengths of the first group can include one or more wavelengths within the range between 968 nm and 982 nm, and the pump laser of one or more wavelengths of the second group can include one or more wavelengths within the range between 968 nm and 982 nm.

[0066] Clause 6: The method according to any one of Clauses 1 to 5, wherein the laser of one or more communication wavelengths can include one or more wavelengths in one or more of the C band, L band, S band, O band, E band, and U band.

[0067] Clause 7: The method according to any one of Clauses 1 to 6, wherein injecting the pump laser of one or more wavelengths of the first group and the second group into the optical fiber can generate gain in the laser of one or more communication wavelengths.

[0068] Clause 8: The method according to any one of Clauses 1 to 7, wherein the pump laser of one or more wavelengths of the first group and the second group can be generated from both sides of a single laser chip.

[0069] Clause 9: The method according to any one of Clauses 1 to 8, wherein the pump laser of one or more wavelengths of the first group and the second group can be generated from two outputs on one side of a single laser chip.

[0070] Clause 10: The method according to any one of Clauses 1 to 9, wherein the pump laser of one or more wavelengths of the first group and the second group can be generated from two laser chips.

[0071] Clause 11: The method according to any one of Clauses 1 to 10, wherein the pump laser of one or more wavelengths of the first group and the second group can be generated from one side of a single laser.

[0072] Clause 12: The method according to any one of Clauses 1 to 11, wherein: the pump laser of one or more wavelengths of the first group can include a wavelength of 974 nm ± 1.0 nm; and the pump laser of one or more wavelengths of the second group can include a wavelength of 976 nm ± 1.0 nm.

[0073] Clause 13: The method according to any one of Clauses 1 to 12, wherein: the pump laser of one or more wavelengths of the first group can include wavelengths of 974 nm ± 1.0 nm and 974 nm ± 1.0 nm; and the pump laser of one or more wavelengths of the second group can include wavelengths of 972 nm ± 1.0 nm and 978 nm ± 1.0 nm or 976 nm ± 1.0 nm and 978 nm ± 1.0 nm.

[0074] Clause 14: The method according to any one of Clauses 1 to 13, wherein the optical fiber can be doped with erbium.

[0075] Clause 15: The method according to any one of Clauses 1 to 14, wherein the wavelengths of the first group and the second group can be injected into the optical fiber via one or more combiners or multiplexers.

[0076] Clause 16: The method according to any one of Clauses 1 to 14, wherein the pump laser of one or more wavelengths of the first group can include one or more wavelengths in the range between 1470 nm and 1490 nm, and the pump laser of one or more wavelengths of the second group can include one or more wavelengths in the range between 1470 nm and 1490 nm.

[0077] Although the present disclosure has been described in detail for purposes of illustration based on the currently considered most practical and preferred embodiments, it should be understood that such details are for that purpose only and the present disclosure is not limited to the disclosed embodiments, but on the contrary, is intended to cover modifications and equivalent arrangements within the spirit and scope of the appended claims. For example, it should be understood that the present disclosure contemplates, to the extent possible, the combination of one or more features of any embodiment with one or more features of any other embodiment.

Claims

1. A method of amplification in an optical fiber, the optical fiber having an input end for receiving laser light of one or more communication wavelengths from one or more laser transmitters and an output end for outputting the laser light of the one or more communication wavelengths to one or more laser receivers, the method comprising: (a) injecting pump laser light of one or more wavelengths of a first set between the input end and the output end of the optical fiber through one or more pump lasers; and (b) injecting pump laser light of one or more wavelengths of a second set between the input end and the output end of the optical fiber through the one or more pump lasers, wherein: the wavelengths of the pump laser light of the first set and the pump laser light of the second set injected into the optical fiber are different from each other within a range between 968 nm and 982 nm or between 1470 nm and 1490 nm, and cause inversion in the optical fiber, and the wavelengths of the pump laser light of the first set and the pump laser light of the second set injected into the optical fiber are different from the laser light of the one or more communication wavelengths.

2. The method according to claim 1, wherein, The pump laser light of one or more wavelengths of the first set and the pump laser light of one or more wavelengths of the second set are injected into the optical fiber in the same direction towards the output end of the optical fiber.

3. The method according to claim 1, wherein The pump laser light of one or more wavelengths of the first set and the pump laser light of one or more wavelengths of the second set are injected into the optical fiber in the same direction towards the input end of the optical fiber.

4. The method according to claim 1, wherein The pump laser light of one or more wavelengths of the first set and the pump laser light of one or more wavelengths of the second set are injected into the optical fiber in different directions.

5. The method according to claim 1, wherein: the pump laser light of one or more wavelengths of the first set includes one or more wavelengths within a range between 968 nm and 982 nm; and the pump laser light of one or more wavelengths of the second set includes one or more wavelengths within a range between 968 nm and 982 nm.

6. The method according to claim 1, wherein, The laser light of the one or more communication wavelengths includes one or more wavelengths among one or more of the C band, L band, S band, O band, E band, and U band.

7. The method according to claim 1, wherein Injecting the pump laser light of one or more wavelengths of the first set and the pump laser light of one or more wavelengths of the second set into the optical fiber generates gain in the laser light of the one or more communication wavelengths.

8. The method according to claim 1, wherein The pump laser light of one or more wavelengths of the first set and the pump laser light of one or more wavelengths of the second set are generated from both sides of a single laser chip.

9. The method according to claim 1, wherein, The pump laser light of one or more wavelengths of the first set and the pump laser light of one or more wavelengths of the second set are generated from two outputs on one side of a single laser chip.

10. The method according to claim 1, wherein The pump laser light of one or more wavelengths of the first set and the pump laser light of one or more wavelengths of the second set are generated from two laser chips.

11. According to the method described in claim 1, wherein, The pump laser light of one or more wavelengths of the first set and the pump laser light of one or more wavelengths of the second set are generated from one side of a single laser.

12. The method according to claim 1, wherein: The pump laser of one or more wavelengths in the first group includes a wavelength of 974 nm ± 1.0 nm; and The pump laser of one or more wavelengths in the second group includes a wavelength of 976 nm ± 1.0 nm.

13. The method according to claim 1, wherein: The pump laser of one or more wavelengths in the first group includes wavelengths of 974 nm ± 1.0 nm and 976 nm ± 1.0 nm; and The pump laser of one or more wavelengths in the second group includes wavelengths of 972 nm ± 1.0 nm and 978 nm ± 1.0 nm or 976 nm ± 1.0 nm and 978 nm ± 1.0 nm.

14. The method according to claim 1, wherein The optical fiber is doped with erbium.

15. The method according to claim 1, wherein The wavelengths of the first group and the wavelengths of the second group are injected into the optical fiber via one or more combiners or multiplexers.

16. The method according to claim 1, wherein: The pump laser of one or more wavelengths in the first group includes one or more wavelengths in the range between 1470 nm and 1490 nm; and The pump laser of one or more wavelengths in the second group includes one or more wavelengths in the range between 1470 nm and 1490 nm.

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