Dual-wavelength laser and relay amplifier

Abstract

This application provides a dual-wavelength laser and a repeater amplifier, belonging to the field of optical fiber communication technology. The dual-wavelength laser includes a three-level laser module, a four-level laser module, and a first pump source. The gain medium of both the three-level and four-level laser modules is optical fiber at least doped with ytterbium ions. The first pump source outputs pump light of a first wavelength to the three-level laser module. The three-level laser module absorbs the first wavelength pump light, radiates light of a second wavelength, and outputs unused first pump light from the first wavelength pump light to the four-level laser module. The four-level laser module absorbs this first pump light and radiates light of a third wavelength. Using a dual-wavelength laser of this application, two different wavelengths of laser light can be output.

Description

Technical Field

[0001] This application relates to the field of optical fiber communication technology, and in particular to a dual-wavelength laser and a repeater amplifier. Background Technology

[0002] In single-mode fiber optic communication, the signal light intensity in the fiber will continuously decrease as the transmission distance increases during long-distance transmission. The low signal-to-noise ratio will degrade the signal quality and may even cause the signal to be submerged in noise. Therefore, repeater amplifiers are needed to amplify the signal light.

[0003] In related technologies, when transmitting multi-band signal light in single-mode fiber, the signal light of multiple bands needs to be amplified by repeater amplifiers. Repeater amplifiers all require pump sources to provide pump light. Different bands of signal light may require different pump light, thus necessitating multiple wavelength pump sources. For example, when transmitting short (S) band, conventional (C) band, and long (L) band signal light in single-mode fiber, the S band signal light uses a 1050nm pump source, the C band signal light requires a 980nm pump source, and the L band signal light also requires a 980nm pump source. Therefore, when transmitting multi-band signal light in single-mode fiber, multiple wavelength lasers need to be used simultaneously to provide pump light. Summary of the Invention

[0004] This application provides a dual-wavelength laser and a repeater amplifier, which can output two different wavelengths of light, so that two different wavelengths of light can be provided using a single laser.

[0005] In a first aspect, this application provides a dual-wavelength laser, which includes a three-level laser module, a four-level laser module, and a first pump source; the gain medium of the three-level laser module is an optical fiber at least doped with ytterbium ions, and the gain medium of the four-level laser module is an optical fiber at least doped with ytterbium ions; the first pump source is used to output pump light of a first wavelength to the three-level laser module; the three-level laser module is used to absorb the pump light of the first wavelength, radiate light of a second wavelength, and output unused first pump light of the first wavelength pump light to the four-level laser module; the four-level laser module is used to absorb the first pump light and radiate light of a third wavelength.

[0006] In the scheme shown in this application, the dual-wavelength laser includes a three-level laser module, a four-level laser module, and a first pump source. The three-level laser module generates light of the second wavelength using a three-level system, and the four-level laser module generates light of the third wavelength using a four-level system. By cascading the four-level laser module after the three-level laser module, the remaining pump light from the three-level laser module can be provided to the four-level laser module, thereby improving the pump light utilization rate.

[0007] In one example, the three-level laser module includes a first gain medium, a first wavelength division multiplexing (WDM), and a first reflection unit. The first gain medium is located between the first WDM and the first reflection unit. The first WDM is used to output pump light of a first wavelength to the first gain medium. The first gain medium is used to absorb the pump light of the first wavelength, output light of a second wavelength bidirectionally, and output unused first pump light of the first wavelength to the first reflection unit. The first reflection unit is used to reflect the output light of the second wavelength to the first gain medium and transmit the first pump light to the four-level laser module. The first WDM is also used to output the light of the second wavelength output by the first gain medium.

[0008] In the scheme shown in this application, the three-level laser module includes a first gain medium, a first WDM and a first reflection unit. The three-level laser module includes fewer components and has a simple structure.

[0009] In one example, the three-level laser module further includes a second reflective unit, which has a lower reflectivity for the second wavelength of light than the first reflective unit for the second wavelength of light, and a higher transmittance for the second wavelength of light than the reflectivity of the first reflective unit for the second wavelength of light; the first WDM is located between the first gain medium and the second reflective unit; the first WDM is also used to output the second wavelength of light to the second reflective unit; the second reflective unit is used to form a resonant cavity for selecting the second wavelength of light together with the first gain medium and the first reflective unit.

[0010] In the scheme shown in this application, a resonant cavity is formed in the three-level laser module by a high-reflectivity device, a low-reflectivity device and a first gain medium. The resonant cavity can select the second wavelength of light and make the second wavelength of light travel back and forth in the resonant cavity multiple times, so that the power of the second wavelength of light is relatively high.

[0011] In one example, the four-level laser module includes a third reflective unit and a second gain medium; the third reflective unit is used to transmit the first pump light output by the three-level laser module to the second gain medium; the second gain medium is used to absorb the first pump light and output light of a third wavelength bidirectionally; the third reflective unit is also used to reflect the light of the third wavelength.

[0012] In the scheme shown in this application, the four-level laser module includes a third reflection unit and a second gain medium. The four-level laser module includes fewer components and has a simple structure.

[0013] In one example, the dual-wavelength laser further includes a second pump source, and the four-level laser module further includes a second WDM; the second gain medium is located between the third reflective unit and the second WDM; the second pump source is used to output a fourth wavelength pump light to the second WDM; the second WDM is used to output the fourth wavelength pump light to the second gain medium; the second gain medium is used to absorb the first pump light and the fourth wavelength pump light, and bidirectionally output the third wavelength light; the second WDM is also used to output the third wavelength light output by the second gain medium.

[0014] In the scheme shown in this application, the dual-wavelength laser includes a first pump source and a second pump source. The first pump source directly provides pump light to the three-level laser module, and the second pump source directly provides pump light to the four-level laser module. By adopting a bidirectional pumping method, the output laser power of the dual-wavelength laser can be flexibly adjusted by adjusting the power of the first pump source and the second pump source.

[0015] In one example, the four-level laser module includes a third reflective unit, a second gain medium, and a second WDM; the second gain medium is located between the third reflective unit and the second WDM; the second WDM is used to output the first pump light output by the three-level laser module to the second gain medium; the second gain medium is used to absorb the first pump light and output light of a third wavelength bidirectionally; the third reflective unit is used to reflect the light of the third wavelength; the second WDM is also used to output the light of the third wavelength output by the second gain medium.

[0016] In one example, the dual-wavelength laser further includes a first isolation module located between the three-level laser module and the four-level laser module. The first isolation module is used to allow the pump light of the first wavelength to pass through while preventing the light generated by the three-level laser module from passing through the light generated by the four-level laser module.

[0017] In the solution shown in this application, by setting a first isolation module, the three-level laser module and the four-energy laser module will not interfere with each other.

[0018] In one example, the dual-wavelength laser includes a second pump source; the second pump source is used to output a fourth wavelength pump light to the second WDM; the second gain medium is used to absorb the first pump light and the fourth wavelength pump light, output the third wavelength light bidirectionally, and output the second pump light unused in the fourth wavelength pump light to the third reflection unit; the third reflection unit is also used to output the second pump light to the three-level laser module.

[0019] In the scheme shown in this application, the dual-wavelength laser also includes a second pump source, which directly provides pump light to the four-level laser module. The four-level laser module can also provide the unused second pump light from the second pump source to the three-level laser module, so as to maximize the power of the pump light and avoid the high-power pump light from being difficult to be completely absorbed in a short distance, thereby maximizing the utilization rate of the pump light.

[0020] In one example, the dual-wavelength laser further includes a second isolation module and a third isolation module; the second isolation module is located between the second WDM and the three-level laser module, and is configured to allow the first wavelength pump light and the fourth wavelength pump light to pass through, while preventing the light generated by the three-level laser module from passing through the light generated by the four-level laser module; the third isolation module is located between the three-level laser module and the third reflection unit, and is configured to allow the first wavelength pump light and the fourth wavelength pump light to pass through, while preventing the light generated by the three-level laser module from passing through the light generated by the four-level laser module.

[0021] In the scheme shown in this application, by setting a second isolation module and a third isolation module, the three-level laser module and the four-energy laser module will not interfere with each other.

[0022] In one example, the four-level laser module further includes a fourth reflecting unit, which has a lower reflectivity for the third wavelength of light than the third reflecting unit, and a higher transmittance for the third wavelength of light than the reflectivity of the third wavelength of light; the second WDM is located between the second gain medium and the fourth reflecting unit; the fourth reflecting unit is used to form a resonant cavity for selecting the third wavelength of light together with the third reflecting unit and the second gain medium.

[0023] In the scheme shown in this application, a resonant cavity is formed by a high-reflectivity device, a low-reflectivity device, and a second gain medium in the four-level laser module. The resonant cavity can select the light of the third wavelength and make the light of the third wavelength travel back and forth in the resonant cavity multiple times, so that the power of the light of the third wavelength is relatively high.

[0024] In one example, the first wavelength of the pump light is a multimode pump light.

[0025] In one example, the fourth wavelength of pump light is multimode pump light.

[0026] In one example, the first wavelength is 915nm or 975nm, the second wavelength ranges from 970nm to 980nm, and the third wavelength ranges from 1030nm to 1100nm.

[0027] In one example, both the first and second reflective units are reflective fiber Bragg gratings.

[0028] In one example, both the third and fourth reflective units are reflective fiber Bragg gratings.

[0029] Secondly, this application provides a repeater amplifier comprising a third WDM, a third gain medium, a fourth WDM, a fourth gain medium, and a dual-wavelength laser as described in the first aspect or any possible implementation thereof; the third WDM is used to couple a second wavelength of light to the third gain medium; the third gain medium is used to absorb the second wavelength of light and amplify the signal light of the first band passing through the repeater amplifier; the fourth WDM is used to couple a third wavelength of light to the fourth gain medium; the fourth gain medium is used to absorb the third wavelength of light and amplify the signal light of the second band passing through the repeater amplifier.

[0030] In the scheme shown in this application, when the relay amplifier amplifies two signal lights of different wavelengths, a dual-wavelength laser can be used as the pump source, which reduces the implementation complexity of the relay amplifier. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of a dual-wavelength laser provided in an exemplary embodiment of this application;

[0032] Figure 2 This is a schematic diagram of the operating energy levels of a ytterbium-doped laser provided in an exemplary embodiment of this application;

[0033] Figure 3 This is an absorption and radiation spectrum of ytterbium ions provided in an exemplary embodiment of this application;

[0034] Figure 4 This is a schematic diagram of the structure of a dual-wavelength laser provided in an exemplary embodiment of this application;

[0035] Figure 5 This is a schematic diagram of the structure of a dual-wavelength laser provided in an exemplary embodiment of this application;

[0036] Figure 6 This is a schematic diagram of the structure of a dual-wavelength laser provided in an exemplary embodiment of this application;

[0037] Figure 7 This is a schematic diagram of the structure of a dual-wavelength laser provided in an exemplary embodiment of this application;

[0038] Figure 8 This is a schematic diagram of the structure of a dual-wavelength laser provided in an exemplary embodiment of this application;

[0039] Figure 9 This is a schematic diagram of the structure of a dual-wavelength laser provided in an exemplary embodiment of this application;

[0040] Figure 10 This is a schematic diagram of the structure of a dual-wavelength laser provided in an exemplary embodiment of this application;

[0041] Figure 11 This is a schematic diagram of the structure of a dual-wavelength laser provided in an exemplary embodiment of this application;

[0042] Figure 12 This is a schematic diagram of the structure of a dual-wavelength laser provided in an exemplary embodiment of this application;

[0043] Figure 13 This is a schematic diagram of the structure of a dual-wavelength laser provided in an exemplary embodiment of this application;

[0044] Figure 14 This is a schematic diagram of the structure of a dual-wavelength laser provided in an exemplary embodiment of this application;

[0045] Figure 15 This is a schematic diagram of the structure of a dual-wavelength laser provided in an exemplary embodiment of this application;

[0046] Figure 16 This is a schematic diagram of the structure of a dual-wavelength laser provided in an exemplary embodiment of this application;

[0047] Figure 17 This is a schematic diagram of the structure of a dual-wavelength laser provided in an exemplary embodiment of this application;

[0048] Figure 18 This is a schematic diagram of the structure of a dual-wavelength laser provided in an exemplary embodiment of this application;

[0049] Figure 19 This is a schematic diagram of the structure of a relay amplifier provided in an exemplary embodiment of this application;

[0050] Figure 20 This is a schematic diagram of the structure of a relay amplifier provided in an exemplary embodiment of this application;

[0051] Figure 21 This is a schematic diagram of the structure of a relay amplifier provided in an exemplary embodiment of this application;

[0052] Figure 22 This is a schematic diagram of the structure of a relay amplifier provided in an exemplary embodiment of this application.

[0053] Illustration

[0054] 1. Three-level laser module; 2. Four-level laser module; 3. First pump source; 4. Second pump source;

[0055] 5. First isolation module; 6. Second isolation module; 7. Third isolation module;

[0056] 11. First gain medium; 12. First WDM; 13. First reflection unit; 14. Second reflection unit;

[0057] 21. Third reflective unit; 22. Second gain medium; 23. Second WDM; 24. Fourth reflective unit;

[0058] 31. First pump unit; 32. Second pump unit; 41. Third pump unit; 42. Fourth pump unit;

[0059] 01. Third WDM; 02. Third gain medium; 03. Fourth WDM; 04. Fourth gain medium; 05. Power splitter; 06. Fifth WDM; 07. Fifth gain medium; 08. Sixth WDM; 09. Seventh WDM. Detailed Implementation

[0060] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0061] The following explains some terms and concepts involved in the embodiments of this application.

[0062] 1. Double-clad optical fiber consists of a core, inner cladding, outer cladding, and a protective layer. The core serves as the laser transmission channel, while the inner cladding acts as the pump light channel, providing multimode pump light. The outer cladding is made of a polymer material with a lower refractive index than the inner cladding. This creates a large cross-section and large numerical aperture optical waveguide between the inner and outer cladding, allowing high-power, multimode pump light with a large numerical aperture to couple into the fiber. The protective layer can be a rigid plastic used to protect the fiber.

[0063] 2. A three-level system, comprising a ground state E0, a metastable state E1, and a higher energy level E2, with the lower energy level being the ground state E0 and the upper energy level being the metastable state E1. The luminescence process is as follows: Under the action of a pump source, particles in the ground state E0 are pumped to the higher energy level E2. At the higher energy level E2, these particles undergo a non-radiative transition to the metastable state E1, accumulating in E1. When the difference between the number of particles in the metastable state E1 and the number of particles in the ground state E0 satisfies a threshold condition, the particles in the metastable state E1 transition back to the ground state E0, thus emitting light. Throughout the luminescence process of the three-level system, a considerable number of particles are maintained in the ground state E0.

[0064] 3. A four-level system, comprising a ground state E0, an excited state E1, a metastable state E2, and a higher energy level E2. The lower energy level is the excited state E1, and the upper energy level is the metastable state E2. The luminescence process is as follows: Under the action of a pump source, particles in the ground state E0 are pumped to the higher energy level E3. The particles then undergo a non-radiative transition to the metastable state E2, accumulating on it. When the difference between the number of particles in the metastable state E2 and the number of particles in the excited state E1 satisfies a threshold condition, the particles in the metastable state E2 transition to the excited state E1, thus emitting light.

[0065] The background of the embodiments of this application is described below.

[0066] In single-mode fiber optic communication, the signal strength in the fiber will continuously decrease as the transmission distance increases during long-distance transmission. A low signal-to-noise ratio will degrade the signal quality and may even cause the signal to be submerged in noise. Therefore, repeater amplifiers are needed to amplify the signal strength.

[0067] In related technologies, when transmitting multi-band signal light in single-mode fiber, the signal light of multiple bands needs to be amplified by repeater amplifiers. Repeater amplifiers all require pump sources to provide pump light. Different bands of signal light may require different pump light, thus necessitating multiple pump sources of different wavelengths. For example, when transmitting S-band, C-band, and L-band signal light in single-mode fiber, the S-band signal light requires a 1050nm pump source, the C-band signal light requires a 980nm pump source, and the L-band signal light also requires a 980nm pump source.

[0068] This application provides a dual-wavelength laser that can output two different wavelengths of light, which can be used as pump light. Thus, when two different wavelengths of pump source are needed, only one dual-wavelength laser is required.

[0069] The structure of the dual-wavelength laser in the embodiments of this application is described below.

[0070] Figure 1 An exemplary schematic diagram of a dual-wavelength laser is provided. See also... Figure 1The dual-wavelength laser includes a three-level laser module 1, a four-level laser module 2, and a first pump source 3.

[0071] In the three-level laser module 1, population inversion is achieved by generating laser light through a three-level system. The gain medium of the three-level laser module 1 is an optical fiber at least doped with ytterbium ions.

[0072] In the four-level laser module 2, population inversion is achieved by generating laser light through a four-level system. The gain medium of the four-level laser module 2 is an optical fiber at least doped with ytterbium ions.

[0073] The first pump source 3 outputs pump light of a first wavelength, which is input into the three-level laser module 1. The three-level laser module 1 absorbs the pump light of the first wavelength and radiates light of a second wavelength, which is a single-mode laser. It then outputs unused pump light from the first wavelength pump light to the four-level laser module 2; this unused pump light is referred to as the first pump light. The four-level laser module 2 absorbs this first pump light and radiates light of a third wavelength, which is also a single-mode laser. In this way, a dual-wavelength laser can radiate both the second and third wavelengths of light.

[0074] It should be noted that the three-level laser module 1 generates laser light through a three-level system. A three-level system requires a high population inversion, resulting in a relatively large amount of residual pump light. The cascaded four-level laser module 2 generates laser light through a four-level system. A four-level system requires a lower population inversion than a three-level system; therefore, the four-level laser module 2 can utilize the residual pump light from the three-level laser module 1, improving pump utilization.

[0075] Figure 2 A schematic diagram of the operating energy levels of a ytterbium-doped laser is provided. See also... Figure 2 Ytterbium ions have seven energy levels, from a to g, from lowest to highest. Specifically, when the first, second, and third wavelengths are 915 nm, 977 nm, and greater than 1000 nm but less than 2000 nm respectively, the energy levels involved are g, e, and a when the 915 nm pump light pumps the 977 nm light. When the 915 nm pump light pumps the light greater than 1000 nm but less than 2000 nm, a total of four energy levels are involved, such as g, e, d, and a at 1069 nm.

[0076] Figure 3 Absorption and radiation spectra of ytterbium ions are provided. Figure 3 In the study, the absorption peaks of ytterbium ions are located at 915 nm and 975 nm, while the radiation peaks are located at 976 nm and 1025 nm. Figure 3 In the image, at the 976nm position, the absorption and emission segments overlap.

[0077] See Figure 3 In one example, the first wavelength is 915nm or 975nm, the second wavelength ranges from 970nm to 980nm, and the third wavelength ranges from 1030nm to 1100nm. For example, the second wavelength is 976nm and the third wavelength is 1050nm.

[0078] In one example, the first wavelength of the pump light is a multimode pump light, which is a single longitudinal mode and a transverse multimode pump light.

[0079] In this embodiment of the application, in the dual-wavelength laser shown above, the second wavelength light generated by the three-level laser module 1 may be output to the four-level laser module 2, affecting the four-level laser module 2. The third wavelength light generated by the four-level laser module 2 may also be output to the three-level laser module 1, affecting the three-level laser module 1.

[0080] To minimize the interference between the three-level laser module 1 and the four-level laser module 2, an isolation module can be installed between them. For details, see [link to documentation]. Figure 4 The dual-wavelength laser shown has a first isolation module 5 between the three-level laser module 1 and the four-level laser module 2. The first isolation module 5 allows the pump light of the first wavelength to pass through, and at least blocks the light of the third wavelength from passing through.

[0081] Optionally, the first isolation module 5 is a two-port device, including an input port and an output port.

[0082] In one example, the first isolation module 5 can be an isolator to achieve unidirectional transmission of broadband optical signals. For example, the optical fiber used in the isolator is a multimode fiber with a numerical aperture (NA) of 0.22 (105 / 125 μm), and a magneto-optical crystal is used to achieve unidirectional transmission of broadband optical signals. In this embodiment, the wavelength range of the broadband optical signal can be 950–1100 nm, where "105" indicates a core diameter of 105 μm and "125" indicates a cladding diameter of 125 μm. Specifically, the direction of the isolator is set to allow light transmission from the three-level laser module 1 to the four-level laser module 2, while blocking light from the four-level laser module 2 to the three-level laser module 1. Thus, when the first isolation module 5 uses an isolator, the third wavelength light generated by the four-level laser module 2 will not be output to the three-level laser module 1 and will not affect the three-level laser module 1.

[0083] In another example, the first isolation module 5 can be a filter. For instance, this filter can achieve light intensity scattering in a certain wavelength band. With the first, second, and third wavelengths being 915nm, 976nm, and 1050nm respectively, this wavelength band can be 950–1100nm. The filter uses 105 / 125um multimode fiber with NA = 0.22. Long-period fiber gratings are used to write light intensity scattering in the 950–1100nm range on this multimode fiber. Thus, when the first isolation module 5 uses a filter, the second wavelength light generated by the three-level laser module 1 will not be output to the four-level laser module 2, and will not affect the four-level laser module 2. Similarly, the third wavelength light generated by the four-level laser module 2 will not be output to the three-level laser module 1, and will not affect the three-level laser module 1.

[0084] In this application embodiment, the three-level laser module 1 has multiple structures, and two possible structures are provided below.

[0085] In one example, in a dual-wavelength laser, the three-level laser module 1 includes a first gain medium 11, a first WDM 12, and a first reflection unit 13. Figure 5 An exemplary schematic diagram of a dual-wavelength laser is provided. See also... Figure 5 The first gain medium 11 is located between the first WDM 12 and the first reflection unit 13. The first gain medium 11 is an optical fiber at least doped with ytterbium ions. In addition to being doped with ytterbium ions, the first gain medium 11 may also be doped with other ions. This application embodiment does not limit this.

[0086] The first WDM12 is connected to the first pump source 3. Pump light of the first wavelength is input to the first gain medium 11 through the first WDM12. The first gain medium 11 absorbs the pump light of the first wavelength and outputs light of the second wavelength bidirectionally. It also outputs the first pump light of the first wavelength to the first reflection unit 13. Here, "bidirectional output" means that the first gain medium 11 outputs light of the second wavelength to the first WDM12 and to the first reflection unit 13. The first WDM12 can also output the received light of the second wavelength.

[0087] The first reflective unit 13 transmits pump light of the first wavelength and reflects light of the second wavelength, exhibiting a relatively high reflectivity for the second wavelength, thus constituting a high-reflectivity device. The first reflective unit 13 transmits the first pump light to the four-level laser module 2. The four-level laser module 2 absorbs the first pump light and radiates light of the third wavelength. The first reflective unit 13 can also reflect the second wavelength light back to the first gain medium 11.

[0088] In another example, in a dual-wavelength laser, the second wavelength of light is filtered by forming a resonant cavity using high-reflectivity and low-reflectivity devices in the three-level laser module 1. Figure 6 An exemplary schematic diagram of a dual-wavelength laser is provided. See also... Figure 6 The three-level laser module 1 includes a first gain medium 11, a first WDM 12, a first reflective unit 13, and a second reflective unit 14. The first reflective unit 13 has a higher reflectivity for light of the second wavelength than the second reflective unit 14, and the second reflective unit 14 has a higher transmittance for light of the second wavelength than its reflectivity. The first reflective unit 13 is a high-reflectivity device, and the second reflective unit 14 is a low-reflectivity device. The first WDM 12 and the second reflective unit 14 are connected via optical fiber.

[0089] The first WDM12 outputs light of the second wavelength to the second reflecting unit 14. The second reflecting unit 14 transmits most of the received light of the second wavelength and reflects a small portion of the light of the second wavelength back to the first gain medium 11. The first reflecting unit 13, the first gain medium 11, and the second reflecting unit 14 form a resonant cavity, which enables the selection of light of the second wavelength.

[0090] exist Figure 6 In the dual-wavelength laser shown, because there is a resonant cavity in the three-level laser module 1, the second wavelength light passes through the first gain medium 11 multiple times, so the power of the second wavelength light can be higher.

[0091] In one example, the first gain medium 11 can be a ytterbium-doped optical fiber and can be connected to a 6 / 125DCF low-loss connection to achieve a low-loss connection between the single-mode signal in the fiber core and the multimode signal in the inner cladding, where the multimode signal refers to the pump light signal.

[0092] In one example, the first WDM12 can be a three-port device, specifically a three-port fiber combiner for pump and signal light, including a pump light input port, a signal light transmission port, and a common transmission port for both the signal and pump light. When the first WDM12 is a three-port device, it indicates the presence of a single pump source; that is, the first pump source 3 outputs a single pump light to the three-level laser module 1. For example, the first pump source 3 could be a 915nm multimode pump laser (laser diode, LD) or a 975nm multimode pump laser.

[0093] In another example, the first WDM12 can also be a four-port device, specifically a (2+1)x1 pump light / signal fiber combiner, which includes two pump light input ports, one signal light transmission port, and one common transmission port for both the signal and pump lights. When the first WDM12 is a four-port device, it indicates the existence of two pump sources. That is, the first pump source 3 outputs two pump lights to the three-level laser module 1. These two pump lights constitute the first wavelength pump light described above. The wavelengths of both pump lights are the first wavelength, and their powers can be equal or unequal. For example, the first pump source 3 includes a first pump unit 31 and a second pump unit 32, both of which are 915nm multimode pumped lasers. Both the first pump unit 31 and the second pump unit 32 are connected to the first WDM 12. Alternatively, the first pump source 3 includes a first pump unit 31 and a second pump unit 32, both of which are 975nm multimode pumped lasers. Both the first pump unit 31 and the second pump unit 32 are connected to the first WDM 12. See [link to relevant documentation]. Figure 7 The dual-wavelength laser shown.

[0094] In the first WDM12 port, the pump light input port can be a 105 / 125μm multimode fiber with NA=0.22, where "105" indicates a core diameter of 105μm and "125" indicates a cladding diameter of 125μm. The signal light transmission port can be a 6 / 125μm double-clad fiber (DCF), and the common transmission port for both signal and pump light can be a 20 / 125 DCF. "6" indicates a core diameter of 6μm, "125" indicates an outer cladding diameter of 125μm and a typical inner cladding diameter of 105μm, and "20" indicates a core diameter of 20μm.

[0095] Optionally, the first reflective element 13 is a reflective fiber bragg grating (FBG), and specifically a high-reflectivity FBG. The first reflective element 13 can be obtained by etching in a single-mode fiber; this embodiment does not limit the type of single-mode fiber.

[0096] The second reflective element 14 is also a reflective FBG, and it is a low-reflectivity FBG. The second reflective element 14 can be obtained by writing in a DCF.

[0097] In this application embodiment, the four-level laser module 2 has multiple structures, and several possible structures are provided below.

[0098] In one example, in a dual-wavelength laser, the four-level laser module 2 includes a third reflecting unit 21 and a second gain medium 22. Figure 8 An exemplary schematic diagram of a dual-wavelength laser is provided. See also... Figure 8 The third reflection unit 21 transmits the pump light of the first wavelength and reflects the light of the third wavelength. It has a high reflectivity for the third wavelength, making it a high-reflectivity device. The third reflection unit 21 is connected to the three-level laser module 1. Specifically, the third reflection unit 21 is connected to the first reflection unit 13 in the three-level laser module 1 via optical fiber. The third reflection unit 21 is also connected to the second gain medium 22, which is connected to the output port of the third wavelength light in the dual-wavelength laser.

[0099] The three-level laser module 1 outputs unused first pump light. This first pump light is incident on the third reflection unit 21, which transmits it and inputs it into the second gain medium 22. The second gain medium 22 absorbs the first pump light and radiates light of a third wavelength. This third wavelength light is bidirectional; "bidirectional output" here refers to the third reflection unit 21 outputting the third wavelength light and also outputting it to the output port of the dual-wavelength laser. After receiving the third wavelength light, the third reflection unit 21 reflects it and inputs it back into the second gain medium 22, thus amplifying the third wavelength light again. The output port of the dual-wavelength laser outputs the third wavelength light, which can be used as a pump source for a repeater amplifier. This application embodiment does not limit the use of the third wavelength light.

[0100] In another example, it is also possible to directly provide pump light to the four-level laser module 2. See also Figure 9 The dual-wavelength laser shown also includes a second pump source 4. The four-level laser module 2 includes a third reflector unit 21, a second gain medium 22, and a second WDM 23. The second gain medium 22 is located between the third reflector unit 21 and the second WDM 23. The second WDM 23 is located between the second gain medium 22 and the second pump source 4.

[0101] The second pump source 4 can output pump light of a fourth wavelength, which may be the same as or different from the first wavelength. The second pump source 4 outputs the fourth wavelength pump light to the second WDM 23. The second gain medium 22 absorbs the first and fourth wavelength pump light and radiates a third wavelength light. This third wavelength light is bidirectionally output; "bidirectionally output" here refers to the third reflection unit 21 outputting the third wavelength light and also outputting it to the second WDM 23. The third wavelength light is incident on the third reflection unit 21 and the second WDM 23. After receiving the third wavelength light, the third reflection unit 21 reflects it and inputs it back into the second gain medium 22, achieving further amplification of the third wavelength light. The second WDM 23 also outputs the third wavelength light as the third wavelength light output by the dual-wavelength laser.

[0102] exist Figure 9 In the dual-wavelength laser shown, a second pump source 4 is present, which enables the pump light used by the four-level laser module 2 to have a relatively high power, thereby resulting in a relatively high power for the third wavelength light. Moreover, by employing a bidirectional pumping mode, the output power of the second and third wavelength light can be flexibly adjusted by regulating the power of the first pump source 3 and the second pump source 4.

[0103] In another example, in a dual-wavelength laser, the third wavelength of light is filtered by forming a resonant cavity using high-reflectivity and low-reflectivity devices in the four-level laser module 2. Figure 10 An exemplary schematic diagram of a dual-wavelength laser is provided. See also... Figure 10 The four-level laser module 2 includes a third reflecting unit 21, a second gain medium 22, and a fourth reflecting unit 24. The third reflecting unit 21 has a higher reflectivity for light of the third wavelength than the fourth reflecting unit 24, while the fourth reflecting unit 24 has a higher transmittance for light of the third wavelength than its reflectivity. The third reflecting unit 21 is a high-reflectivity device, and the fourth reflecting unit 24 is a low-reflectivity device. The second gain medium 22 is located between the third reflecting unit 21 and the fourth reflecting unit 24. The third reflecting unit 21 is connected to the three-level laser module 1, and the fourth reflecting unit 24 is connected to the output port of the dual-wavelength laser.

[0104] The three-level laser module 1 outputs unused first pump light. This first pump light is incident on the third reflecting unit 21, which transmits it and inputs it into the second gain medium 22. The second gain medium 22 absorbs the first pump light and radiates light of a third wavelength. This third wavelength light is bidirectional, meaning it is output from both the third reflecting unit 21 and the fourth reflecting unit 24. Upon receiving the third wavelength light, the third reflecting unit 21 reflects it and inputs it back into the second gain medium 22, further amplifying the third wavelength light. The third wavelength light is then incident on the fourth reflecting unit 24, which transmits most of it, allowing the third wavelength light to be output from the output port of the dual-wavelength laser. The fourth reflecting unit 24 reflects a small portion of the third wavelength light to the second gain medium 22. The fourth reflecting unit 24, the second gain medium 22, and the third reflecting unit 21 form a resonant cavity. This resonant cavity allows the third wavelength light to travel back and forth multiple times, which not only makes the power of the third wavelength light output by the dual-wavelength laser relatively high, but also selects the accurate third wavelength light.

[0105] In another example, in a dual-wavelength laser, the four-level laser module 2 forms a resonant cavity through high-reflectivity and low-reflectivity devices to filter the light of the third wavelength, and the four-level laser module 2 corresponds to a direct pump light. Figure 11 An exemplary schematic diagram of this dual-wavelength laser is provided. See also... Figure 11 The dual-wavelength laser also includes a second pump source 4, and the four-level laser module 2 includes a third reflection unit 21, a second gain medium 22, a second WDM 23, and a fourth reflection unit 24.

[0106] Corresponding to the third wavelength of light, the third reflecting unit 21 is a high-reflection device, and the fourth reflecting unit 24 is a low-reflection device. The second gain medium 22 is located between the third reflecting unit 21 and the second WDM 23, and the second WDM 23 is located between the second gain medium 22 and the fourth reflecting unit 24, and also between the second gain medium 22 and the second pump source 4. The third reflecting unit 21 is connected to the three-level laser module 1, and the fourth reflecting unit 24 is connected to the output port of the dual-wavelength laser.

[0107] The three-level laser module 1 outputs unused first pump light. This first pump light is incident on the third reflecting unit 21, which transmits it and inputs it into the second gain medium 22. The second gain medium 22 absorbs the first pump light and radiates a third wavelength of light. This third wavelength light is bidirectional, meaning it is output by both the third reflecting unit 21 and the second WDM 23. After receiving the third wavelength light, the third reflecting unit 21 reflects it and inputs it back into the second gain medium 22, amplifying the third wavelength light again. The third wavelength light is then incident on the second WDM 23, which outputs it to the fourth reflecting unit 24. The fourth reflecting unit 24 transmits most of the third wavelength light, allowing it to be output from the output port of the dual-wavelength laser. The fourth reflection unit 24 reflects a small portion of the third wavelength light, which is then input to the second gain medium 22 through the second WDM 23. The fourth reflection unit 24, the third reflection unit 21, and the second gain medium 22 form a resonant cavity. This resonant cavity allows the third wavelength light to travel back and forth multiple times, which not only makes the power of the third wavelength light output by the dual-wavelength laser relatively high, but also selects the accurate third wavelength light.

[0108] In another example, in a dual-wavelength laser, the third reflection unit 21 in the four-level laser module 2 is located at the end furthest from the three-level laser module 1. Figure 12 An exemplary schematic diagram of this dual-wavelength laser is provided. See also... Figure 12 The four-level laser module 2 includes a third reflective unit 21, a second gain medium 22, and a second WDM 23. The second WDM 23 is a three-port device, as described below. The second gain medium 22 is located between the third reflective unit 21 and the second WDM 23. The second WDM 23 is connected to the three-level laser module 1, specifically, the second WDM 23 is connected to the first reflective unit 13.

[0109] The three-level laser module 1 outputs a first pump light to the second WDM 23, which in turn outputs the first pump light to the second gain medium 22. The second gain medium 22 absorbs the first pump light and radiates light of a third wavelength. This third wavelength light is bidirectional; "bidirectional output" here refers to the third reflection unit 21 outputting the third wavelength light and also outputting it to the second WDM 23. After receiving the third wavelength light, the third reflection unit 21 reflects it and inputs it back into the second gain medium 22, thus amplifying the third wavelength light again. The second WDM 23 outputs the third wavelength light to the output port of the dual-wavelength laser, which can serve as the pump source for a repeater amplifier.

[0110] In another example, in a dual-wavelength laser, the third reflection unit 21 in the four-level laser module 2 is located at the end away from the three-level laser module 1, and the four-level laser module 2 uses a resonant cavity formed by high-reflection and low-reflection devices to filter the light of the third wavelength. Figure 13 An exemplary schematic diagram of this dual-wavelength laser is provided. See also... Figure 13 The four-level laser module 2 includes a third reflecting unit 21, a second gain medium 22, a second WDM 23, and a fourth reflecting unit 24. The second WDM 23 is a three-port device, as described below. The second gain medium 22 is located between the third reflecting unit 21 and the second WDM 23. The second WDM 23 is connected to the three-level laser module 1, specifically, the second WDM 23 is connected to the first reflecting unit 13, and the second WDM 23 is located between the second gain medium 22 and the fourth reflecting unit 24.

[0111] Corresponding to the third wavelength of light, the third reflecting unit 21 is a high-reflection device, and the fourth reflecting unit 24 is a low-reflection device. The three-level laser module 1 outputs a first pump light to the second WDM 23, and the second WDM 23 outputs the first pump light to the second gain medium 22. The second gain medium 22 absorbs the first pump light and radiates light of the third wavelength. This third wavelength light is bidirectionally output; here, "bidirectionally output" refers to the third reflecting unit 21 outputting the third wavelength light and also outputting the third wavelength light to the second WDM 23. After receiving the third wavelength light, the third reflecting unit 21 reflects the third wavelength light and inputs it back into the second gain medium 22, thereby amplifying the third wavelength light again. The second WDM 23 outputs light of the third wavelength to the fourth reflecting unit 24. The fourth reflecting unit 24 reflects a small portion of the third wavelength light, which is then input to the second gain medium 22 via the second WDM 23. The fourth reflecting unit 24, the second gain medium 22, and the third reflecting unit 21 form a resonant cavity. This resonant cavity allows the third wavelength light to travel back and forth multiple times, resulting in higher power output of the third wavelength light from the dual-wavelength laser and precise selection of the third wavelength. This third wavelength light can be used as the pump source for a repeater amplifier.

[0112] In another example, Figure 12 The dual-wavelength laser shown can also directly provide a fourth wavelength pump light to the four-level laser module 2, and send the unused second pump light from this pump light to the three-level laser module 1 for use. See [link to documentation]. Figure 14 .

[0113] For details, see Figure 15The dual-wavelength laser shown also includes a second pump source 4. The four-level laser module 2 includes a third reflecting unit 21, a second gain medium 22, and a second WDM 23. The second gain medium 22 is located between the third reflecting unit 21 and the second WDM 23. The second WDM 23 is connected to the three-level laser module 1, specifically, it is connected to the first reflecting unit 13. The second WDM 23 is also connected to the second pump source 4. The third reflecting unit 21 is also connected to the three-level laser module 1, specifically, it is connected to the first WDM 12.

[0114] In the three-level laser module 1, the first reflection unit 13 outputs a first pump light to the second WDM 23. The second pump source 4 can output a fourth wavelength pump light, which can be the same as or different from the first wavelength. The second pump source 4 outputs the fourth wavelength pump light to the second WDM 23. The second gain medium 22 absorbs the first and fourth wavelength pump light and radiates a third wavelength light, which is bidirectionally output. The third wavelength light is incident on the third reflection unit 21 and the second WDM 23. After receiving the third wavelength light, the third reflection unit 21 reflects the third wavelength light and inputs it back into the second gain medium 22, thus amplifying the third wavelength light again. The second WDM 23 also outputs the third wavelength light as the third wavelength light output by the dual-wavelength laser.

[0115] Because pump light has pump conversion efficiency, it is impossible to convert 100% of it into the required laser light. Therefore, the second gain medium 22 can transmit the unused second pump light from the fourth wavelength pump light to the third reflection unit 21. The third reflection unit 21 transmits the second pump light to the first WDM 12, and the first WDM 12 inputs the second pump light to the first gain medium 11. The first gain medium 11 can also absorb the second pump light and radiate light of the second wavelength.

[0116] exist Figure 15 In the dual-wavelength laser shown, since there is also a second pump source 4, the power limitation on the pump light can be relaxed, the power of the pump light can be increased as much as possible, a higher power laser output can be obtained, and the high power pump light can be avoided from being difficult to be completely absorbed in a short distance, thus improving the utilization rate of the pump light.

[0117] Moreover, by adjusting the power of the first pump source 3 and the second pump source 4, the two wavelengths of light output by the dual-wavelength laser can be freely adjusted within a certain range.

[0118] In another example, in a dual-wavelength laser, wavelength selection is achieved in the four-level laser module 2 by forming a resonant cavity using high-reflectivity and low-reflectivity devices. Figure 15In the dual-wavelength laser shown, the four-level laser module 2 also includes a fourth reflection unit 24, see [link / reference]. Figure 16 The dual-wavelength laser shown, the four-level laser module 2, includes a third reflecting unit 21, a second gain medium 22, and a fourth reflecting unit 24. Corresponding to the third wavelength of light, the third reflecting unit 21 is a high-reflectivity device, and the fourth reflecting unit 24 is a low-reflectivity device. The second gain medium 22 is located between the third reflecting unit 21 and the second WDM 23. The third reflecting unit 21 is connected to the first WDM 12, the first reflecting unit 13 is connected to the second WDM 23, the second WDM 23 is connected to the fourth reflecting unit 24, and the second gain medium 22 is located between the second WDM 23 and the third reflecting unit 21.

[0119] The fourth reflection unit 24, the third reflection unit 21, and the second gain medium 22 form a resonant cavity. This resonant cavity allows the third wavelength light to travel back and forth multiple times, which not only makes the power of the third wavelength light output by the dual-wavelength laser relatively high, but also selects the accurate third wavelength light.

[0120] exist Figure 15 and Figure 16 In the dual-wavelength laser shown, there is a second pump source 4, which enables the pump light used by the four-level laser module 2 to have a relatively high power, thereby making the power of the third wavelength light relatively high.

[0121] exist Figure 15 and Figure 16 In the dual-wavelength laser shown, the three-level laser module 1 may or may not include a second reflection unit 14.

[0122] In another example, Figure 15 and Figure 16 To prevent the second and third wavelengths of light from interfering with each other, an isolation module can be placed between the three-level laser module 1 and the four-level laser module 2 in the dual-wavelength laser shown. Specifically, the dual-wavelength laser also includes a second isolation module 6 and a third isolation module 7, see [link to documentation]. Figure 17 The dual-wavelength laser shown.

[0123] The second isolation module 6 is located between the second WDM23 and the three-level laser module 1. The second isolation module 6 allows the first and fourth wavelength pump light to pass through, while blocking the second and third wavelength light from passing through.

[0124] The third isolation module 7 is located between the three-level laser module 1 and the third reflection unit 21. The third isolation module 7 allows the first and fourth wavelength pump light to pass through, while blocking the second and third wavelength light from passing through.

[0125] exist Figure 17 In the dual-wavelength laser shown, the second wavelength of light will not be input into the four-level laser module 2, and the third wavelength of light will not be input into the three-level laser module 1. Therefore, the three-level laser module 1 and the four-level laser module 2 will not interfere with each other.

[0126] In one example, the second isolation module 6 and the third isolation module 7 can be filters, etc., mentioned above.

[0127] In another example, the second isolation module 6 and the third isolation module 7 can be the isolators mentioned above. The second isolation module 6 cannot prevent the second wavelength of light from entering the four-level laser module 2, and the third isolation module 7 cannot prevent the third wavelength of light from entering the three-level laser module 1.

[0128] In one example, in Figure 15 In the dual-wavelength laser shown, the third reflection unit 21 can also output unused pump light from the first pump light to the three-level laser module 1. Specifically, the third reflection unit 21 outputs the unused pump light to the first WDM 12. The first WDM 12 outputs the unused pump light to the first gain medium 11, which can also absorb the unused pump light and radiate light of the second wavelength. In this way, the first wavelength pump light can be recycled, improving the conversion efficiency of the pump light.

[0129] In one example, the fourth wavelength of the pump light is a multimode pump light.

[0130] In one example, the second gain medium 22 can be a ytterbium-doped optical fiber and can be connected to a 6 / 125DCF low-loss connection to achieve a low-loss connection between the single-mode signal in the fiber core and the multimode signal in the inner cladding, where the multimode signal refers to the pump light signal.

[0131] In one example, the third WDM23 can be a three-port device, specifically a three-port fiber combiner for pump and signal light, including a pump light input port, a signal light transmission port, and a common transmission port for both the signal and pump light. When the third WDM23 is a three-port device, it indicates the presence of a single pump source; that is, the second pump source 4 outputs a single pump light to the four-level laser module 2. For example, the second pump source 4 could be a 915nm multimode pump laser or a 975nm multimode pump laser.

[0132] In another example, the third WDM23 can also be a four-port device, specifically a (2+1)x1 pump / signal fiber combiner, which includes two pump input ports, one signal transmission port, and one common transmission port for both the signal and pump lights. When the third WDM23 is a four-port device, it indicates the existence of two pump sources. That is, the second pump source 4 outputs two pump lights to the four-level laser module 2. These two pump lights form the fourth wavelength pump light described earlier. Both pump lights have the fourth wavelength, and their powers can be equal or unequal. For example, the second pump source 4 includes a third pump unit 41 and a fourth pump unit 42, both of which are 915nm multimode pumped lasers. Both the third pump unit 41 and the fourth pump unit 42 are connected to the second WDM 23. Alternatively, the second pump source 4 includes a third pump unit 41 and a fourth pump unit 42, both of which are 975nm multimode pumped lasers. Both the third pump unit 41 and the fourth pump unit 42 are connected to the second WDM 23. See [link to relevant documentation]. Figure 18 The dual-wavelength laser shown.

[0133] In the third WDM23 port, the pump light input port can be a 105 / 125μm multimode fiber with NA=0.22, where "105" indicates a core diameter of 105μm and "125" indicates a cladding diameter of 125μm. The signal light transmission port can be a 6 / 125μm DCF, and the common transmission port for both signal and pump light can be a 20 / 125 DCF. "6" indicates a core diameter of 6μm, "125" indicates an outer cladding diameter of 125μm, and a typical inner cladding diameter of 105μm. "20" indicates a core diameter of 20μm.

[0134] It should be noted that, in Figures 15 to 17 In the dual-wavelength laser shown, the first WDM12 is a four-port device, and the first pump source 3 provides only one pump beam of the first wavelength. The second WDM23 is a four-port device, and the second pump source 4 provides only one pump beam of the fourth wavelength. When the first pump source 3 provides two pump beams of the first wavelength, the first WDM12 is a five-port device. When the second pump source 4 provides two pump beams of the fourth wavelength, the second WDM23 is a five-port device.

[0135] In one example, the third reflective element 21 is a reflective FBG, and specifically a high-reflectivity FBG. The third reflective element 21 can be obtained by etching in a single-mode fiber; however, this application embodiment does not limit the type of single-mode fiber.

[0136] The fourth reflective element 24 is also a reflective FBG, and a low-reflectivity FBG. The fourth reflective element 24 can be obtained by writing in a DCF.

[0137] exist Figures 7 to 17 In the dual-wavelength laser shown, the specific structure of the three-level laser module 1 can be adopted as follows: Figure 5 or Figure 6 The structure of the three-level laser module 1 shown is illustrated.

[0138] In this embodiment, compared to the 915nm pump light, the theoretical quantum efficiency of the three-level laser module 1 is higher (99%), and the theoretical quantum efficiency of the four-level laser module 2 is higher (92%), effectively improving the utilization rate of the pump light. Therefore, the lengths of the first gain medium 11 and the second gain medium 22 can be further reduced. Furthermore, the pump light output from the first pump source 3 and the second pump source 4 also contains pump light that is not used by the dual-wavelength laser. This portion of pump light can be directly used for post-amplification in the L-band, further maximizing the utilization of the pump light and improving its efficiency.

[0139] In this embodiment, by cascading a three-level laser module 1 and a four-level laser module 2, the pump light of the first wavelength is converted into light of the second and third wavelengths, which can make full use of the pump light of the first wavelength and improve the utilization rate of the pump light.

[0140] In this embodiment of the application, a relay amplifier is also provided, see [link to relevant documentation]. Figure 19 The relay amplifier shown includes a third WDM01, a third gain medium 02, a fourth WDM03, a fourth gain medium 04, and the dual-wavelength laser described above.

[0141] The third WDM01 couples the second wavelength light to the third gain medium 02, which absorbs the second wavelength light and amplifies the signal light in the first band after passing through the repeater amplifier. The fourth WDM03 couples the third wavelength light to the fourth gain medium 04, which absorbs the third wavelength light and amplifies the signal light in the second band after passing through the repeater amplifier.

[0142] For example, the second wavelength is 980nm, the first band is the C band, the third wavelength is 1050nm, and the second band is the S band.

[0143] In this embodiment of the application, another relay amplifier is also provided, see [link to relevant documentation]. Figure 20The relay amplifier shown includes a third WDM01, a third gain medium 02, a fourth WDM03, a fourth gain medium 04, a power splitter 05, a fifth WDM06 and a fifth gain medium 07, and the dual-wavelength laser described above.

[0144] The second wavelength of light is input to the power beam splitter 05 and split into two beams. The third WDM 01 couples one beam of the second wavelength light to the third gain medium 02, which absorbs the second wavelength light and amplifies the signal light in the first band after passing through the repeater amplifier. The fifth WDM 06 couples one beam of the second wavelength light to the fifth gain medium 07, which absorbs the second wavelength light and amplifies the signal light in the third band after passing through the repeater amplifier.

[0145] The fourth WDM03 couples the third wavelength light to the fourth gain medium 04, which absorbs the third wavelength light and amplifies the second band signal light after passing through the repeater amplifier.

[0146] For example, the second wavelength is 980nm, the first band is the C band, the third band is the L band, the third wavelength is 1050nm, and the second band is the S band.

[0147] In this application embodiment, another type of repeater amplifier is also provided, see [link to relevant documentation]. Figure 21 The relay amplifier shown includes a third WDM01, a third gain medium 02, a fourth WDM03, a fourth gain medium 04, a power splitter 05, a fifth WDM06, a fifth gain medium 07, a sixth WDM08, a seventh WDM09, and the dual-wavelength laser described above.

[0148] The signal light includes signal light in the first band, the second band, and the third band. The signal light is input to the sixth WDM08 of the repeater amplifier. The sixth WDM08 separates the signal light in the first band, the second band, and the third band and inputs them to the third WDM01, the fifth WDM06, and the fourth WDM03, respectively.

[0149] The second wavelength of light is input to the power beam splitter 05 and split into two beams. The third WDM 01 couples one beam of the second wavelength light to the third gain medium 02, which absorbs the second wavelength light and amplifies the signal light in the first band after passing through it. The fifth WDM 06 couples the second wavelength light to the fifth gain medium 07, which absorbs the second wavelength light and amplifies the signal light in the third band after passing through it. The power of the two beams split by the power beam splitter 05 are the first power and the second power, respectively. The magnitudes of the first power and the second power can be set according to actual needs.

[0150] The fourth WDM03 couples the third wavelength light to the fourth gain medium 04. The fourth gain medium 04 absorbs the third wavelength light and amplifies the second band signal light that has passed through the fourth gain medium 04.

[0151] The seventh WDM09 combines the amplified signal light from the first band, the second band, and the third band into a single signal light, which is then output from the repeater amplifier.

[0152] For example, the second wavelength is 974nm, the first band is the C band, the third band is the L band, the third wavelength is 1050nm, and the second band is the S band.

[0153] In this embodiment of the application, another relay amplifier is also provided, see [link to relevant documentation]. Figure 22 The relay amplifier shown, Figure 22 The relay amplifier shown is Figure 21 The repeater amplifier shown is similar, but the difference lies in that the power splitter 05 splits the second wavelength light into three beams, with the powers of the three beams being the third, fourth, and fifth powers, respectively. The magnitudes of the third, fourth, and fifth powers can be set according to actual needs. Two of the three beams are... Figure 21 The repeater amplifier has the same function. Another beam is input to the fourth WDM03 and coupled to the fourth gain medium 04 through the fourth WDM03. The fourth gain medium 04 absorbs the third wavelength light and the second wavelength light, and amplifies the signal light of the second band that has passed through the fourth gain medium 04.

[0154] In this application, the terms "first" and "second," etc., are used to distinguish identical or similar items that have substantially the same function and purpose. It should be understood that there is no logical or temporal dependency between "first" and "second," nor does it limit the quantity or order of execution. It should also be understood that although the following description uses the terms "first" and "second," etc., to describe various elements, these elements should not be limited by the terms. These terms are merely used to distinguish one element from another. For example, without departing from the scope of various examples, a first pump source can be referred to as a second pump source, and similarly, a second pump source can be referred to as a first pump source. Both a first pump source and a second pump source can be pump sources, and in some cases, they can be separate and distinct pump sources.

[0155] In this application, the term "at least one" means one or more, and the term "multiple" means two or more.

[0156] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A dual-wavelength laser, characterized by, It includes a three-level laser module (1), a four-level laser module (2), and a first pump source (3); The gain medium of the three-level laser module (1) is an optical fiber doped with at least ytterbium ions, and the three-level laser module (1) is implemented through a three-level system. The gain medium of the four-level laser module (2) is an optical fiber doped with at least ytterbium ions, and the four-level laser module (2) is implemented through a four-level system. The first pump source (3) is used to output pump light of the first wavelength to the three-level laser module (1); The three-level laser module (1) is used to absorb the pump light of the first wavelength through the gain medium, radiate the light of the second wavelength, and output the first pump light that is not used in the pump light of the first wavelength to the four-level laser module (2). The four-level laser module (2) is used to absorb the first pump light through the gain medium and radiate light of a third wavelength, wherein the second wavelength is different from the third wavelength.

2. The dual-wavelength laser of claim 1, wherein, The three-level laser module (1) includes a first gain medium (11), a first wavelength division multiplexer (12) and a first reflection unit (13), wherein the first gain medium (11) is located between the first wavelength division multiplexer (12) and the first reflection unit (13); The first wavelength division multiplexer (12) is used to output pump light of the first wavelength to the first gain medium (11); The first gain medium (11) is used to absorb the pump light of the first wavelength, output the light of the second wavelength in both directions, and output the first pump light that is not used in the pump light of the first wavelength to the first reflection unit (13); The first reflection unit (13) is used to reflect and output the second wavelength of light to the first gain medium (11) and transmit the first pump light to the four-level laser module (2). The first wavelength division multiplexer (12) is also used to output the second wavelength of light output by the first gain medium (11).

3. The dual-wavelength laser of claim 2, wherein, The three-level laser module (1) further includes a second reflection unit (14), the second reflection unit (14) having a lower reflectivity for light of the second wavelength than the first reflection unit (13) for light of the second wavelength, and the second reflection unit (14) having a higher transmittance for light of the second wavelength than the reflectivity for light of the second wavelength. The first wavelength division multiplexer (12) is located between the first gain medium (11) and the second reflection unit (14); The first wavelength division multiplexer (12) is also used to output light of the second wavelength to the second reflection unit (14); The second reflective unit (14) is used to form a resonant cavity for selecting light of the second wavelength together with the first gain medium (11) and the first reflective unit (13).

4. The dual-wavelength laser of claim 1, wherein, The four-level laser module (2) includes a third reflection unit (21) and a second gain medium (22); The third reflection unit (21) is used to transmit and output the first pump light output by the three-level laser module (1) to the second gain medium (22); The second gain medium (22) is used to absorb the first pump light and output the third wavelength light bidirectionally; The third reflective unit (21) is also used to reflect light of the third wavelength.

5. The dual-wavelength laser of claim 4, wherein, The dual-wavelength laser also includes a second pump source (4), and the four-level laser module (2) also includes a second wavelength division multiplexer (23). The second gain medium (22) is located between the third reflection unit (21) and the second wavelength division multiplexer (23); The second pump source (4) is used to output a fourth wavelength pump light to the second wavelength division multiplexer (23); The second wavelength division multiplexer (23) is used to output the fourth wavelength pump light to the second gain medium (22); The second gain medium (22) is used to absorb the first pump light and the fourth wavelength pump light, and output the third wavelength light bidirectionally; The second wavelength division multiplexer (23) is also used to output the third wavelength of light output by the second gain medium (22).

6. The dual-wavelength laser of claim 1, wherein, The four-level laser module (2) includes a third reflection unit (21), a second gain medium (22), and a second wavelength division multiplexer (23). The second gain medium (22) is located between the third reflection unit (21) and the second wavelength division multiplexer (23); The second wavelength division multiplexer (23) is used to output the first pump light output by the three-level laser module (1) to the second gain medium (22); The second gain medium (22) is used to absorb the first pump light and output light of the third wavelength in both directions; The third reflective unit (21) is used to reflect light of the third wavelength; The second wavelength division multiplexer (23) is also used to output the third wavelength of light output by the second gain medium (22).

7. The dual-wavelength laser of any of claims 1 to 6, wherein, The dual-wavelength laser also includes a first isolation module (5); The first isolation module (5) is located between the three-level laser module (1) and the four-level laser module (2); The first isolation module (5) is used to allow the pump light of the first wavelength to pass through and to prevent the light generated by the four-level laser module (2) from passing through.

8. The dual-wavelength laser of claim 6, wherein, The dual-wavelength laser includes a second pump source (4). The second pump source (4) is used to output a fourth wavelength pump light to the second wavelength division multiplexer (23); The second gain medium (22) is used to absorb the first pump light and the fourth wavelength pump light, output the third wavelength light bidirectionally, and output the second pump light that is not used in the fourth wavelength pump light to the third reflection unit (21); The third reflection unit (21) is also used to output the second pump light to the three-level laser module (1).

9. The dual-wavelength laser of claim 8, wherein, The dual-wavelength laser also includes a second isolation module (6) and a third isolation module (7). The second isolation module (6) is located between the second wavelength division multiplexer (23) and the three-level laser module (1). The second isolation module (6) is used to allow the pump light of the first wavelength and the pump light of the fourth wavelength to pass through, and to prevent the light generated by the three-level laser module (1) and the light generated by the four-level laser module (2) from passing through. The third isolation module (7) is located between the three-level laser module (1) and the third reflection unit (21). The third isolation module (7) is used to allow the pump light of the first wavelength and the pump light of the fourth wavelength to pass through, and to prevent the light generated by the three-level laser module (1) and the light generated by the four-level laser module (2) from passing through.

10. The dual-wavelength laser of any of claims 4-6 and 8-9, wherein, The four-level laser module (2) further includes a fourth reflection unit (24), the fourth reflection unit (24) having a lower reflectivity for the third wavelength light than the third reflection unit (21) for the third wavelength light, and the fourth reflection unit (24) having a higher transmittance for the third wavelength light than the reflectivity for the third wavelength light. The second wavelength division multiplexer (23) is located between the second gain medium (22) and the fourth reflection unit (24); The fourth reflective unit (24) is used to form a resonant cavity for selecting light of the third wavelength together with the third reflective unit (21) and the second gain medium (22).

11. The dual-wavelength laser of any one of claims 1 to 6, wherein, The pump light of the first wavelength is a multimode pump light.

12. The dual-wavelength laser of claim 5 or 8, wherein, The fourth wavelength of pump light is multimode pump light.

13. The dual-wavelength laser of any of claims 1-6, wherein, The first wavelength is 915nm or 975nm, the second wavelength ranges from 970nm to 980nm, and the third wavelength ranges from 1030nm to 1100nm.

14. The dual-wavelength laser according to claim 3, characterized in that, Both the first reflective unit (13) and the second reflective unit (14) are reflective fiber Bragg gratings.

15. The dual-wavelength laser of claim 10, wherein, Both the third reflective unit (21) and the fourth reflective unit (24) are reflective fiber Bragg gratings.

16. A repeater amplifier characterized by, It includes a third wavelength division multiplexer, a third gain medium, a fourth wavelength division multiplexer, a fourth gain medium, and a dual-wavelength laser as described in any one of claims 1 to 15; The third wavelength division multiplexer is used to couple the second wavelength of light to the third gain medium; The third gain medium is used to absorb the light of the second wavelength and amplify the signal light of the first band after passing through the repeater amplifier; The fourth wavelength division multiplexer is used to couple the third wavelength of light to the fourth gain medium; The fourth gain medium is used to absorb the light of the third wavelength and amplify the signal light of the second band after passing through the relay amplifier.

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