Raman fiber laser and optical amplifier

Abstract

The invention provides a Raman fiber laser and an optical amplifier, and belongs to the technical field of optical communication. The Raman fiber laser comprises a plurality of pump light assemblies, a combiner, a multi-wavelength reflector, a Raman gain fiber and a multi-wavelength output device, each pump light assembly is connected with the combiner, the combiner is connected with the multi-wavelength reflector, and the Raman gain optical fiber is located between the multi-wavelength reflector and the multi-wavelength output device; the plurality of pump light assemblies are used for outputting optical signals with multiple wavelengths to the combiner; the combiner is used for combining the optical signals with multiple wavelengths into a combined signal and outputting the combined signal; the multi-wavelength reflector is used for inputting the combined wave signal to the Raman gain optical fiber and reflecting the middle Raman laser and the target Raman laser corresponding to each wavelength in multiple wavelengths; and the multi-wavelength output device is used for reflecting the middle Raman laser corresponding to each wavelength and outputting the target Raman laser corresponding to each wavelength. By adopting the Raman fiber laser, Raman laser with various wavelengths can be output.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical communication technology, in particular to a Raman fiber laser and an optical amplifier. BACKGROUND

[0002] In optical communication networks, optical signals will attenuate during transmission, and various fiber amplifiers are needed to amplify the signal light. At present, in fiber amplifiers, the pump light source is mainly a 980nm and 1480nm semiconductor laser, and the ridge width of the single-mode pump chip physically limits the power evolution, which may be difficult to produce high-power pump light. However, as the number of signal light wavelengths in the optical communication network increases, the demand for pump light power also increases. Moreover, as the number of signal light wavelengths in the optical communication network increases, the wavelength band will cover the conventional (C) + long (L) band, or even wider, and single-wavelength pump light sources may not be able to meet the performance requirements of optical amplifiers. SUMMARY

[0003] The present application provides a Raman fiber laser and an optical amplifier, which can provide a Raman fiber laser that outputs multiple pump lights. The technical solutions adopted are as follows:

[0004] In a first aspect, the present application provides a Raman fiber laser, which includes a plurality of pump light assemblies, a combiner, a multi-wavelength reflector, a Raman gain fiber, and a multi-wavelength output device; each pump light assembly in the plurality of pump light assemblies is connected to the combiner, the combiner is connected to the multi-wavelength reflector, and the Raman gain fiber is located between the multi-wavelength reflector and the multi-wavelength output device; the plurality of pump light assemblies are configured to output optical signals of multiple wavelengths to the combiner; the combiner is configured to combine the optical signals of the multiple wavelengths into a combined signal and output the combined signal; the multi-wavelength reflector is configured to input the combined signal to the Raman gain fiber, reflect an intermediate Raman laser corresponding to each wavelength of the multiple wavelengths to perform Raman energy transfer, and reflect a target Raman laser corresponding to each wavelength; and the multi-wavelength output device is configured to reflect the intermediate Raman laser corresponding to each wavelength to perform Raman energy transfer and output the target Raman laser corresponding to each wavelength.

[0005] In the scheme shown in the present application, in the Raman fiber laser, there are multiple pump light assemblies, the multiple pump light assemblies provide pump light of different wavelengths, the pump light of multiple wavelengths undergoes multi-stage Raman energy transfer through the same section of Raman gain fiber, and Raman laser corresponding to each wavelength of pump light is obtained. In this way, not only multiple wavelengths of Raman laser can be output, but also each wavelength of target Raman laser corresponds to independent pump light, so that the power of Raman laser corresponding to multiple wavelengths can be independently adjusted, and in addition, since the pump light of multiple wavelengths shares one section of Raman gain fiber, the integration degree of the Raman fiber laser is relatively high.

[0006] In an optional manner, the multi-wavelength reflector includes multiple first reflection surfaces corresponding to each wavelength, the multi-wavelength outputter includes second reflection surfaces and output couplers corresponding to each wavelength, for a target wavelength in the multiple wavelengths, the number of the first reflection surfaces corresponding to the target wavelength is equal to the sum of the number of the second reflection surfaces and the number of the output couplers; the multiple first reflection surfaces corresponding to the target wavelength are used to reflect the intermediate Raman laser and the target Raman laser corresponding to the target wavelength output by the Raman gain fiber; the second reflection surfaces corresponding to the target wavelength are used to reflect the intermediate Raman laser corresponding to the target wavelength output by the Raman gain fiber; and the output couplers corresponding to the target wavelength are used to output the target Raman laser corresponding to the target wavelength.

[0007] In the scheme shown in the present application, the multi-wavelength reflector and the multi-wavelength outputter both have multiple reflection surfaces, the multiple reflection surfaces of the multi-wavelength reflector, the multiple reflection surfaces of the multi-wavelength outputter and the Raman gain fiber constitute multiple oscillation cavities to realize multi-stage Raman energy transfer.

[0008] In an optional manner, the multiple first reflection surfaces corresponding to each wavelength are realized by Raman fiber gratings, and the second reflection surfaces and the output couplers corresponding to each wavelength are realized by Raman fiber gratings; or the multiple first reflection surfaces corresponding to each wavelength are realized by film layers of fiber end faces, and the second reflection surfaces and the output couplers corresponding to each wavelength are realized by film layers of fiber end faces.

[0009] In the scheme shown in the present application, the first reflection surface, the second reflection surface and the output coupler can be realized by using Raman fiber gratings or by using film coating of fiber end faces.

[0010] In an optional manner, the wavelength of the target Raman laser corresponding to each wavelength belongs to 1.4 μm to 1.5 μm; the Raman gain fiber is a phosphorus-doped fiber; and the Raman energy transfer in the Raman fiber laser depends on the gain peak at 1330 cm -1 of the phosphorus-doped fiber.

[0011] In an optional mode, the multiple wavelengths include a first wavelength and a second wavelength; the first wavelength and the second wavelength belong to 1-1.1 μm, the first wavelength corresponds to intermediate Raman laser and the second wavelength corresponds to intermediate Raman laser belonging to 1.2-1.3 μm.

[0012] In the scheme shown in the application, the wavelength selection is near the highest Raman gain position, the frequency shift amount of the energy cross transfer can be far away from the gain peak position of the phosphorus-doped fiber, the wavelength will only transfer to the long wave along the designed wavelength path, and the probability of cross transfer is very low.

[0013] In an optional mode, the light signal of each wavelength corresponds to target Raman laser with a wavelength belonging to 1.4-1.5 μm; the Raman gain fiber is a phosphorus-doped fiber; the Raman energy transfer in the Raman fiber laser depends on the gain peaks at 495 cm -1 and 1330 cm -1 positions in the phosphorus-doped fiber.

[0014] In an optional mode, the multiple wavelengths include a first wavelength and a second wavelength; the first wavelength and the second wavelength belong to 1-1.1 μm, the first wavelength corresponds to two-stage intermediate Raman laser belonging to 1.2-1.3 μm and 1.3-14 μm respectively, and the second wavelength corresponds to two-stage intermediate Raman laser belonging to 1.2-1.3 μm and 1.3-14 μm respectively.

[0015] In the scheme shown in the application, the wavelength selection is near the highest Raman gain position, the frequency shift amount of the energy cross transfer can be far away from the gain peak position of the phosphorus-doped fiber, the wavelength will only transfer to the long wave along the designed wavelength path, and the probability of cross transfer is very low.

[0016] In an optional mode, the Raman fiber laser further includes a controller; the controller is connected with each pump light assembly; the controller is used to control the power of the light signal output by each pump light assembly, so as to control the power of the target Raman laser corresponding to each wavelength.

[0017] In the scheme shown in the application, the Raman fiber laser further includes a controller, and the controller can control the pump light power output by each pump light assembly, so as to control the power of the corresponding target Raman laser.

[0018] In an optional mode, each pump light assembly includes a multimode pump light module and an oscillation cavity; the multimode pump light module is used to input multimode pump light to the oscillation cavity; the oscillation cavity is used to output light signals with corresponding wavelengths based on the multimode pump light.

[0019] In the scheme shown in the present application, the pump light assembly adopts a multimode pump light module, which can reduce the cost of the pump light assembly.

[0020] In an alternative, the Raman fiber laser further comprises an isolator and / or a mode field adapter; the isolator and / or the mode field adapter are located on the optical path between the combiner and the multi-wavelength reflector.

[0021] In the scheme shown in the present application, when the isolator exists, it can prevent the optical signal from returning to the pump light assembly, and when the mode field adapter exists, it can reduce the splicing loss between different mode field fibers.

[0022] In a second aspect, the present application provides an optical amplifier, comprising a gain fiber and the Raman fiber laser as described in the first aspect or any of the alternative ways of the first aspect. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a structural schematic diagram of a Raman fiber laser provided by a conventional scheme;

[0024] Figure 2 is a general structural schematic diagram of a doped fiber amplifier provided by an example embodiment of the present application;

[0025] Figure 3 is a structural schematic diagram of an erbium-bismuth co-doped fiber amplifier provided by an example embodiment of the present application;

[0026] Figure 4 is a structural schematic diagram of a Raman fiber amplifier provided by an example embodiment of the present application;

[0027] Figure 5 is a Raman gain spectrum schematic diagram of a phosphorus-doped fiber provided by an example embodiment of the present application;

[0028] Figure 6 is a structural schematic diagram of a Raman fiber laser provided by an example embodiment of the present application;

[0029] Figure 7 is a structural schematic diagram of a Raman fiber laser with two-stage Raman energy transfer provided by an example embodiment of the present application;

[0030] Figure 8 is a schematic diagram of two-stage Raman energy transfer provided by an example embodiment of the present application;

[0031] Figure 9 is a structural schematic diagram of a Raman fiber laser with two-stage Raman energy transfer provided by another example embodiment of the present application;

[0032] Figure 10is a schematic diagram of a Raman fiber laser with three-stage Raman energy transfer provided by an example embodiment of the present application.

[0033] Figure 11 is a schematic diagram of three-stage Raman energy transfer provided by an example embodiment of the present application.

[0034] Figure 12 is a schematic diagram of a Raman fiber laser with three-stage Raman energy transfer provided by another example embodiment of the present application.

[0035] Figure 13 is a schematic diagram of an oscillation cavity implemented by fiber end face coating provided by an example embodiment of the present application.

[0036] Figure 14 is a schematic diagram of output spectrum of a multi-wavelength Raman fiber laser provided by an example embodiment of the present application.

[0037] FIG. Illustration

[0038] 1, pump light assembly; 2, combiner; 3, multi-wavelength reflector; 4, Raman gain fiber; 5, multi-wavelength output device; 6, controller; 7, isolator; 8, mode field adapter; 9, reflector;

[0039] 11, multi-mode pump light module; 12, oscillation cavity; 31, first reflecting surface; 51, second reflecting surface; 52, output coupler. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the present application clearer, the embodiments of the present application will be described in further detail below with reference to the drawings.

[0041] In recent years, with the rapid increase of network traffic, the basic network of operators is also expanding and evolving, such as from 100G to 400G, and then to 800G and 1.6T. In the field of optical communication, with the proposal and rapid development of wide-spectrum optical amplification technology, the development of optical amplification technology has shown a trend of integration of 6THz in the C band to 6THz in the L band, and then to 12THz in the C+L band. However, for optical amplifiers, whether erbium-doped fiber amplifiers (EDFA) and bismuth-doped fiber amplifiers (BDFA), or Raman fiber amplifiers (RFA), the pumping efficiency of wide-spectrum is obviously lower than that of narrow-band amplification system. The requirement for pump power of the wide-spectrum optical amplifier in the C+L band is getting higher and higher, and reducing the cost of pump lasers in optical amplifiers is the key to realizing the continuous evolution of optical amplification.

[0042] At present, 1480nm laser is often used as pump light, and 1480nm laser is generated by a Raman fiber laser. The Stokes shift of the Raman fiber laser is independent of the wavelength of the pump light, and the Raman gain spectrum is wide, so that the output of optical signals of various wavelengths from 1.1μm to 1.6μm can be easily realized. For example, by using the large frequency shift of a phosphorus-doped fiber, 1480nm laser can be obtained by only two cascades, as shown in Figure 1 The 1061nm laser is generated by using a low-cost semiconductor multimode pump to pump a double-clad ytterbium (Yb)-doped fiber, and then the 1061nm laser is used to pump a Raman fiber laser to form a laser cavity by cascading to oscillate and output 1480nm laser. The energy level transfer process is: 1061nm→1236nm→1480nm. In this way, 1480nm laser is generated by cascading a Raman fiber laser, and when it is applied to an optical amplifier in the field of optical communication, the following disadvantages exist:

[0043] 1. The power of 1.4μm laser wavelength is only adjusted by adjusting the power of the multimode pump, but the optical amplifier in the field of optical communication usually has a multi-stage structure, and the pump power between the stages needs to be adjusted independently, otherwise the problems of hole burning suppression and stimulated Raman scattering (SRS) transfer in optical amplification will be affected, resulting in the performance of the optical amplifier being degraded. The concept of hole burning effect is that, in an erbium-doped fiber amplifier, due to the effect of inhomogeneous broadening, the saturated signal light eliminates the common upper level particles (belonging to the homogeneous broadening part) to make the gain of all wavelengths decrease, and also consumes the particles belonging only to the wavelength itself, thereby causing the gain of the wavelength to decrease slightly. This phenomenon is called hole burning effect, which will make the gain of the optical amplifier uneven, thereby leading to performance degradation.

[0044] 2. For an erbium-bismuth co-doped fiber amplifier, the erbium-doped fiber needs to be pumped by 980nm laser to maintain the performance such as noise figure (NF), but for the bismuth-doped fiber, pumping by 980nm laser will cause serious bleaching saturation effect, resulting in the fluorescence performance being reduced. Bleaching saturation refers to that the bismuth-doped fiber is bleached after absorbing 980nm laser, and no longer absorbs light. Usually, the pump light source uses 1460nm or 1480nm, therefore, the erbium-bismuth co-doped fiber amplifier needs to be pumped by two wavelengths of 980nm and 1480nm respectively to achieve the optimal performance. However, it is difficult to generate the two wavelengths by using the same Raman fiber laser, and if two lasers are used, the complexity of the system is increased.

[0045] Recently, it is found through experiments that the pumping effect of the erbium-doped fiber pumped by the wavelength near 1445nm is similar to that of the wavelength of 980nm. Therefore, it is important to generate dual-wavelength laser by cascaded Raman fiber laser, which can reduce the complexity of the pumping light source and cost, and can meet the dual-wavelength pumping requirement at the same time.

[0046] It should be noted that the dual-wavelength is in the range of 1.4μm to 1.5μm, and is not strictly limited to the wavelength.

[0047] Based on this, the application provides a Raman fiber laser capable of generating multiple wavelengths, which can generate multiple wavelengths and realize independent control of the output power of different wavelengths, and meets the performance requirements of the fiber amplifier.

[0048] In the application, the Raman fiber laser is used as the pumping light source of the optical amplifier, and the optical amplifier needs multiple wavelengths of pumping light. The optical amplifier is a doped fiber amplifier, which can be an EDFA or a Raman fiber amplifier. Figure 2 A general structure of the doped fiber amplifier is provided. As shown in Figure 2 The doped fiber amplifier includes a Raman fiber laser, a combiner, a gain fiber (also referred to as a doped fiber), and a filter and other passive optical devices. The Raman fiber laser is connected with the combiner, the gain fiber is located between the combiner and the filter and other passive optical devices, the Raman fiber laser outputs multiple wavelengths of pumping light, the pumping light of one wavelength is combined with the signal light in the combiner to form a beam, and then is input into the gain fiber. When the signal light and the pumping light are transmitted in the gain fiber, the signal light is amplified, and the amplified signal light enters the filter and other passive optical devices, so that other optical signals other than the signal light are filtered out. In this way, the optical amplifier realizes amplification of the signal light. In the application, the signal light can also be referred to as service light. Figure 2 The "X" in the figure indicates that the transmission fiber is fused with the doped fiber.

[0049] Figure 3 A structure diagram of an erbium-bismuth co-doped fiber amplifier is provided. As shown in Figure 3As shown, the erbium-bismuth co-doped fiber amplifier comprises a Raman fiber laser, a first combiner, an erbium-doped fiber, a gain flattening filter, an attenuator, a second combiner and a bismuth-doped fiber, the Raman fiber laser is connected with the first combiner, the first combiner, the erbium-doped fiber, the gain flattening filter, the attenuator, the second combiner and the bismuth-doped fiber are connected in sequence. The first wavelength of pump light output by the Raman fiber laser is coupled to the erbium-doped fiber through the first combiner, the signal light is amplified in the erbium-doped fiber, and then output to the flattening filter. The flattened filter performs flattening filtering on the amplified signal light, and then outputs to the attenuator. The attenuator attenuates the flattened light signal, and then outputs to the bismuth-doped fiber. The second wavelength of pump light output by the Raman fiber laser is coupled to the bismuth-doped fiber through the second combiner. The signal light continues to be amplified in the bismuth-doped fiber and then is output.

[0050] Optionally, after the bismuth-doped fiber, a flattening filter, an attenuator, an isolator and the like can also be arranged.

[0051] In Figure 2 and Figure 3 , the transmission directions of the signal light and the pump light are the same, realizing forward pumping. The transmission directions of the signal light and the pump light can also be opposite, realizing reverse pumping.

[0052] Figure 4 A structural schematic diagram of a distributed reverse Raman fiber amplifier is provided. As shown in the figure, Figure 4 The Raman fiber amplifier comprises a Raman fiber laser and a combiner. The combiner is connected with a transmission fiber in the Raman fiber amplifier. The Raman fiber laser is connected with the combiner. The multiple wavelengths of pump light output by the Raman fiber laser are coupled to the transmission fiber through the combiner. The transmission fiber serves as a gain medium. The signal light is also transmitted in the transmission fiber. The transmission direction of the signal light is opposite to that of the pump light.

[0053] Figure 4 In the distributed optical amplifier, the Raman fiber laser can also be applied to a centralized optical amplifier. The difference between the centralized optical amplifier and the distributed optical amplifier lies in that the centralized optical amplifier is installed at a certain position to amplify the signal light in a centralized manner, that is, there is a special gain fiber in the centralized optical amplifier.

[0054] In the present application, before describing the Raman fiber laser, the gain medium of the Raman fiber laser is first described. The gain medium is an optical fiber with a Raman gain coefficient, such as a fiber doped with germanium (Ge) and a fiber doped with phosphorus. The fiber is called a Raman gain fiber. Figure 5 The gain spectrum of the Raman gain fiber is provided. The horizontal axis is the Raman frequency shift amount, which is simply referred to as the frequency shift amount, and the vertical axis is the Raman gain coefficient. In the present application, the frequency shift amount is 440cm -1and 1330cm -1 The Raman gain peaks at the location were provided by germanium and phosphorus, respectively, cm. -1 It is a unit of wave number. Figure 5 Only a rough schematic diagram of the gain spectrum of the Raman gain fiber is provided, without giving the specific values ​​of the Raman gain coefficients corresponding to each Raman frequency shift.

[0055] Figure 6 A schematic diagram of a Raman fiber laser is provided. Figure 6 As shown, the Raman fiber laser includes multiple pump light components 1, a multiplexer 2, a multi-wavelength reflector 3, a Raman gain fiber 4, and a multi-wavelength output device 5. Each of the multiple pump light components 1 is connected to the multiplexer 2, the multiplexer 2 is connected to the multi-wavelength reflector 3, and the Raman gain fiber 4 is located between the multi-wavelength reflector 3 and the multi-wavelength output device 5.

[0056] Each pump light component 1 outputs an optical signal of a specific wavelength to the combiner 2. Different pump light components output optical signals of different wavelengths, each wavelength serving as the pump light. The combiner 2 combines these multiple wavelengths into a single optical signal, called the combined signal. The combiner 2 inputs this combined signal to the multi-wavelength reflector 3. After passing through the multi-wavelength reflector 3, the combined signal enters the Raman gain fiber 4. For each wavelength, the multi-wavelength reflector 3, the Raman gain fiber 4, and the multi-wavelength outputter 5 constitute multiple oscillating cavities corresponding to that wavelength. These oscillating cavities perform multi-stage Raman energy transfer on the optical signal of that wavelength to obtain the target Raman laser corresponding to that wavelength. The target Raman laser is the laser that needs to be output by the Raman fiber laser, and it is output from the multi-wavelength outputter 5. In addition, intermediate Raman lasers are also obtained during the multi-stage Raman energy transfer process. The intermediate Raman laser is the Raman laser obtained before the target Raman laser is obtained. The multi-wavelength output device 5 reflects the intermediate Raman laser back into the Raman gain fiber 4 for the next stage of Raman energy transfer.

[0057] Thus, adopting Figure 6 The Raman fiber laser shown can output Raman lasers of multiple wavelengths, and each wavelength of Raman laser has an independent pump light, so that the power of the multiple wavelengths of Raman laser can be adjusted independently. In addition, the Raman gain fiber 4 is shared by multiple wavelengths of Raman laser, which can improve the system integration and reduce the system cost.

[0058] In an alternative way, the multi-wavelength reflector 3 comprises a plurality of first reflecting surfaces 31 corresponding to each wavelength, the multi-wavelength outputter 5 comprises a plurality of second reflecting surfaces 51 and output couplers 52 corresponding to each wavelength, and for each wavelength, the number of the first reflecting surfaces 31 is equal to the sum of the number of the second reflecting surfaces 51 and the number of the output couplers 52. Taking a target wavelength as an example, the target wavelength is any wavelength in the plurality of wavelengths, the plurality of first reflecting surfaces 31 comprises a first reflecting surface 31 reflecting the intermediate Raman laser and the target Raman laser, the second reflecting surface 51 has a high reflectivity to the intermediate Raman laser output by the Raman gain fiber 4, for example, the reflectivity is greater than 99%, and the output coupler 52 has a low reflectivity to the target Raman laser output by the Raman gain fiber 4, for example, the output coupler has a reflectivity in the range of 10% to 40%, and the specific reflectivity value is determined according to the length of the Raman gain fiber 4 and the loss in the oscillation cavity and the like. One first reflecting surface 31, the Raman gain fiber 4 and one second reflecting surface 51 form an oscillation cavity, and one first reflecting surface 31, the Raman gain fiber 4 and one output coupler 52 form an oscillation cavity, so that the plurality of first reflecting surfaces 31 can form a plurality of oscillation cavities, in the oscillation cavity with the second reflecting surface 51, the first reflecting surface 31 and the second reflecting surface 51 have a high reflectivity to the intermediate Raman laser, in the oscillation cavity with the output coupler 52, the first reflecting surface 31 has a high reflectivity to the target Raman laser, and the output coupler 32 has a low reflectivity to the target Raman laser. The optical signal of the target wavelength is subjected to multi-stage Raman energy transfer in the plurality of oscillation cavities, and the Raman laser corresponding to the target wavelength is obtained.

[0059] In an alternative way, the wavelength of the Raman laser corresponding to the optical signal of each wavelength belongs to 1.4 μm to 1.5 μm. The Raman gain fiber 4 is a phosphorus-doped fiber, and the multi-stage Raman energy transfer depends on the gain peak at 1330 cm -1 of the phosphorus-doped fiber.

[0060] Alternatively, the wavelength of the optical signal output by the plurality of pump light assemblies 1 comprises a first wavelength and a second wavelength. The first wavelength and the second wavelength belong to 1 μm to 1.1 μm, the intermediate Raman laser corresponding to the first wavelength belongs to 1.2 μm to 1.3 μm, and the intermediate Raman laser corresponding to the second wavelength belongs to 1.2 μm to 1.3 μm. For example, the first wavelength is 1043 nm, the intermediate Raman laser corresponding to the first wavelength is 1212 nm, and the target Raman laser corresponding to the first wavelength is 1445 nm. The second wavelength is 1061 nm, the intermediate Raman laser corresponding to the second wavelength is 1236 nm, and the target Raman laser corresponding to the second wavelength is 1480 nm. In this way, both the first wavelength and the second wavelength are subjected to two-stage Raman energy transfer.

[0061] Figure 7 A structural schematic diagram of the Raman fiber laser is provided. As shown inFigure 7 As shown, the plurality of pump light assemblies 1 includes two pump light assemblies 1. Each pump light assembly 1 includes a multimode pump light module 11, an oscillation cavity 12 and a first combiner. The multimode pump light module 11 is a semiconductor multimode pump laser, outputting a center wavelength of 915 nm, 940 nm or 980 nm. The oscillation cavity 12 includes a gain fiber and a fiber grating with required wavelength high reflectivity and low reflectivity matching, such as the gain fiber is a Yb-doped fiber, the high reflectivity is greater than or equal to 99%, and the low reflectivity is close to 10%. The first combiner is located between the high reflectivity and low reflectivity matching fiber gratings, and the first combiner is connected with the multimode pump light module 11. The low reflectivity fiber grating in each oscillation cavity 12 is connected with the combiner 2 through an optical fiber.

[0062] The plurality of first reflection surfaces 31 corresponding to the first wavelength includes two first reflection surfaces 31, and the second reflection surface 51 and the output coupler 52 are each one. Among the two first reflection surfaces 31, one first reflection surface 31 reflects the intermediate Raman laser of 1212 nm, and the other first reflection surface 31 reflects the target Raman laser of 1445 nm. The plurality of first reflection surfaces 31 corresponding to the second wavelength includes two first reflection surfaces 31, and the second reflection surface 51 and the output coupler 52 are each one. The plurality of first reflection surfaces 31 corresponding to the two wavelengths can be arranged arbitrarily, and the arrangement order has little effect on the Raman laser. The second reflection surface 51 and the output coupler 52 corresponding to the two wavelengths can be arranged arbitrarily, and the arrangement order has little effect on the Raman laser. In Figure 7 It is shown in the figure that the first reflection surface 31, the second reflection surface 51 and the output coupler 52 are all realized by fiber gratings.

[0063] The central wavelength of the multimode pump light outputted by the two multimode pump light modules 11 is 915nm, 940nm or 980nm. The multimode pump light outputted by one multimode pump light module 11 is inputted into the first combiner, and the power of the multimode pump light is set according to actual needs. The first combiner inputs the multimode pump light into the oscillation cavity 12. The oscillation cavity 12 outputs 1043nm light signal through the low reflectivity fiber grating. The multimode pump light outputted by another multimode pump light module 11 is inputted into the first combiner, and the power of the multimode pump light is set according to actual needs. The first combiner inputs the multimode pump light into the oscillation cavity 12. The oscillation cavity 12 outputs 1061nm light signal through the low reflectivity fiber grating. Here, the multimode pump light can also be directly inputted from the fiber grating to the oscillation cavity 12 without using the first combiner. The 1043nm light signal and the 1061nm light signal are combined in the combiner 2 to obtain a combined signal. The combined signal enters the Raman gain fiber 4 through all the first reflecting surfaces 31. The Raman gain fiber 4 is used to provide wide Raman frequency shift. The first reflecting surface 31, the second reflecting surface 51 and the Raman gain fiber 4 reflecting 1212nm light signal constitute an oscillation cavity. The first reflecting surface 31 and the second reflecting surface 51 reflecting 1212nm light signal are first-order Raman fiber gratings. The 1043nm light signal is converted to 1212nm through the Raman gain fiber 4, and is incident to the second reflecting surface 51. The second reflecting surface 51 reflects the 1212nm light signal. The 1212nm light signal enters the Raman gain fiber 4. The Raman gain fiber 4 outputs 1445nm light signal. The first reflecting surface reflecting 1445nm light signal reflects the 1445nm light signal to form an oscillation cavity with the output coupler 52. The oscillation cavity is used to select 1445nm light signal. The output coupler 52 outputs 1445nm light signal. The first reflecting surface 31 and the output coupler 52 reflecting 1445nm light signal are second-order Raman fiber gratings.

[0064] The first reflecting surface 31, the second reflecting surface 51 and the Raman gain fiber 4 reflecting the 1236nm light signal constitute an oscillation cavity, the first reflecting surface 31 and the second reflecting surface 51 reflecting the 1236nm light signal are first order Raman fiber gratings, the 1061nm light signal is converted to 1236nm through the Raman gain fiber 4, is incident to the second reflecting surface 51, the second reflecting surface 51 reflects the 1236nm light signal, the 1236nm light signal enters the Raman gain fiber 4, the Raman gain fiber 4 outputs the 1480nm light signal, the 1480nm light signal is incident to the first reflecting surface reflecting the 1480nm light signal, the first reflecting surface reflects the 1480nm light signal to constitute an oscillation cavity with the output coupler 52, the oscillation cavity is used for selecting the 1480nm light signal, the output coupler 52 outputs the 1480nm light signal, and the first reflecting surface 31 reflecting the 1480nm light signal and the output coupler 52 are second order Raman fiber gratings.

[0065] Figure 8 A multi-stage Raman energy transfer schematic diagram is also provided. As shown in Figure 8 , 1043nm is converted to 1212nm, the frequency shift is 1 / 1043nm-1 / 1212nm=1336cm -1 , 1212nm is further converted to 1445nm, the frequency shift is 1 / 1212nm-1 / 1445nm=1330cm -1 , 1061nm is converted to 1236nm, the frequency shift is 1 / 1061nm-1 / 1236nm=1334cm -1 , 1236nm is further converted to 1480nm, the frequency shift is 1 / 1236nm-1 / 1480nm=1333cm -1 . Since the Raman gain fiber 4 is a phosphorus-doped fiber, the phosphorus-doped fiber has a relatively narrow gain peak near 1330cm -1 (see Figure 3 ), and the wavelength selection is at the highest Raman gain position. Moreover, the dashed arrow in Figure 8 indicates energy cross transfer, the frequency shift from 1043nm to 1236nm is 1497cm -1 , the frequency shift from 1236nm to 1445nm is 1170cm -1 , the frequency shift from 1061nm to 1212nm is 1174cm -1 , and the frequency shift from 1212nm to 1480nm is 1494cm -1 . It can be seen that the frequency shift of the energy cross transfer is far away from the gain peak position (1330cm -1 ) of the phosphorus-doped fiber, and therefore, the wavelength will only be transferred along the intended path to the long wave, and it is difficult to occur energy cross transfer.

[0066] Optionally, the Raman fiber laser further comprises one or more of a controller 6, an isolator 7, a mode field adapter 8, or a plurality of reflectors 9, as shown in Figure 9 The controller 6 is connected with each of the pump light assemblies 1, and the controller 6 can control the power of the light signal output by each of the pump light assemblies 1, thereby controlling the power of the target Raman laser corresponding to each of the wavelengths of the light signal. For example, each of the pump light assemblies 1 comprises a multimode pump light module 11 and an oscillation cavity 12, and the controller 6 controls the power of the light signal output by each of the multimode pump light modules 11, thereby controlling the power of the light signal output by each of the pump light assemblies 1, and further controlling the power of the target Raman laser corresponding to each of the wavelengths of the light signal. The isolator 7 and the mode field adapter 8 are located on the light path between the combiner 2 and the multi-wavelength reflector 3. The isolator 7 is used to prevent the light signal from being input from the multi-wavelength reflector 3 to the combiner 2, so that the light signal output by the multi-wavelength reflector 3 does not affect the pump light assemblies 1. The mode field adapter 8 is used to reduce the fusion loss between different mode field fibers. The plurality of reflectors 9 are located on the output light path of the multi-wavelength output device 5, and the plurality of reflectors 9 respectively reflect the pump light to prevent the pump light from being output from the Raman fiber laser.

[0067] In an optional manner, the wavelength of the Raman laser corresponding to each of the wavelengths of the light signal belongs to 1.4 μm to 1.5 μm. The Raman gain fiber 4 is a phosphorus-doped fiber, and the multi-stage Raman energy transfer depends on the gain peaks at 1330 cm -1 and 495 cm -1 in the phosphorus-doped fiber.

[0068] Optionally, the wavelengths of the light signals output by the plurality of pump light assemblies 1 comprise a first wavelength and a second wavelength. The first wavelength and the second wavelength belong to 1 μm to 1.1 μm, the first wavelength corresponds to two intermediate Raman lasers belonging to 1.2 μm to 1.3 μm and 1.3 μm to 1.4 μm, respectively, and the second wavelength corresponds to two intermediate Raman lasers belonging to 1.2 μm to 1.3 μm and 1.3 μm to 1.4 μm, respectively. For example, the first wavelength is 1080 nm, the two intermediate Raman laser wavelengths corresponding to the first wavelength are 1261 nm and 1345 nm, respectively, and the wavelength of the target Raman laser corresponding to the first wavelength is 1445 nm. The second wavelength is 1090 nm, the two intermediate Raman laser wavelengths corresponding to the second wavelength are 1276 nm and 1363 nm, respectively, and the wavelength of the target Raman laser corresponding to the second wavelength is 1470 nm. In this way, both the first wavelength and the second wavelength are subjected to three-stage Raman energy transfer.

[0069] Figure 10 A structural schematic diagram of the Raman fiber laser is provided. As shown in Figure 10As shown, the plurality of pump light assemblies 1 includes two pump light assemblies 1. Each pump light assembly 1 includes a multimode pump light module 11, an oscillation cavity 12 and a first combiner. The multimode pump light module 11 is a semiconductor multimode pump laser, and outputs a center wavelength of 915, 940 or 980 nm. The oscillation cavity 12 includes a gain fiber and a fiber grating with required high reflectivity and low reflectivity matching, for example, the gain fiber is a Yb-doped fiber, the high reflectivity is greater than or equal to 99%, and the low reflectivity is close to 10%. The first combiner is located between the high reflectivity and low reflectivity matching fiber gratings, and the first combiner is connected with the multimode pump light module 11. The low reflectivity fiber grating in each oscillation cavity 12 is connected with the combiner 2 through an optical fiber.

[0070] For the first wavelength, the plurality of first reflecting surfaces 31 includes three first reflecting surfaces 31, the second reflecting surfaces 51 are two, and the output coupler 52 is one. Among the three first reflecting surfaces 31, one first reflecting surface 31 reflects the intermediate Raman laser of 1261 nm, another first reflecting surface 31 reflects the intermediate Raman laser of 1345 nm, and the other first reflecting surface 31 reflects the target Raman laser of 1445 nm. Among the two second reflecting surfaces 51, one second reflecting surface 51 reflects the intermediate Raman laser of 1261 nm, and the other second reflecting surface 51 reflects the intermediate Raman laser of 1345 nm. The output coupler 52 reflects the target Raman laser of 1445 nm, but the reflectivity is relatively low. For the second wavelength, the plurality of first reflecting surfaces 31 includes three first reflecting surfaces 31, the second reflecting surfaces 51 are two, and the output coupler 52 is one. Among the three first reflecting surfaces 31, one first reflecting surface 31 reflects the intermediate Raman laser of 1276 nm, another first reflecting surface 31 reflects the intermediate Raman laser of 1363 nm, and the other first reflecting surface 31 reflects the target Raman laser of 1470 nm. Among the two second reflecting surfaces 51, one second reflecting surface 51 reflects the intermediate Raman laser of 1276 nm, and the other second reflecting surface 51 reflects the target Raman laser of 1363 nm. The output coupler 52 reflects the target Raman laser of 1470 nm, but the reflectivity is relatively low. The plurality of first reflecting surfaces 31 corresponding to the two wavelengths can be arranged in any order, and the arrangement order has little effect on the Raman laser. The second reflecting surfaces 51 and the output coupler 52 corresponding to the two wavelengths can be arranged in any order, and the arrangement order has little effect on the Raman laser. That is, the order of the first reflecting surface 31, the second reflecting surface 51 and the second reflecting surface 51 can be any, and the first reflecting surface 31, the second reflecting surface 51 and the second reflecting surface 51 are all implemented by fiber gratings in the specific embodiment. Figure 10

[0071] ​The central wavelength of the multimode pump light outputted by the two multimode pump light modules 11 is 915nm, 940nm or 980nm. The multimode pump light outputted by one multimode pump light module 11 is inputted into the first combiner, and the power of the multimode pump light is set according to actual needs. The first combiner inputs the multimode pump light into the oscillation cavity 12. The oscillation cavity 12 outputs the light signal of 1080nm through the low reflectivity fiber grating. The multimode pump light outputted by another multimode pump light module 11 is inputted into the first combiner, and the power of the multimode pump light is set according to actual needs. The first combiner inputs the multimode pump light into the oscillation cavity 12. The oscillation cavity 12 outputs the light signal of 1090nm through the low reflectivity fiber grating. Here, the multimode pump light can also not pass through the first combiner and be directly inputted into the oscillation cavity 12 from the fiber grating. After the light signal of 1080nm and the light signal of 1090nm are combined in the combiner 2, a combined signal is obtained. The combined signal enters the Raman gain fiber 4 through the two first reflecting surfaces 31 corresponding to each wavelength. The Raman gain fiber 4 is used to provide Raman frequency shift. The first reflecting surface 31 reflecting the light signal of 1261nm, the second reflecting surface 51 and the Raman gain fiber 4 constitute an oscillation cavity. The first reflecting surface 31 reflecting the light signal of 1261nm and the second reflecting surface 51 reflecting the light signal of 1261nm are a first-order Raman fiber grating. The light signal of 1080nm is shifted to 1261nm through the Raman gain fiber 4, is incident to the second reflecting surface 51 reflecting the light signal of 1261nm, and the second reflecting surface 51 reflecting the light signal of 1261nm reflects the light signal of 1261nm. The light signal of 1261nm enters the Raman gain fiber 4, the Raman gain fiber 4 outputs the light signal of 1345nm, the light signal of 1345nm is incident to the first reflecting surface reflecting the light signal of 1345nm, the first reflecting surface reflecting the light signal of 1345nm reflects the light signal of 1345nm to form an oscillation cavity with the second reflecting surface reflecting the light signal of 1345nm. The first reflecting surface 31 reflecting the light signal of 1345nm and the second reflecting surface 51 are a second-order Raman fiber grating. The Raman gain fiber 4 outputs the light signal of 1445nm to the first reflecting surface 31 reflecting the light signal of 1445nm. The first reflecting surface 31 reflecting the light signal of 1445nm and the output coupler 52 form an oscillation cavity, which is used to select the light signal of 1445nm. The output coupler 52 outputs the light signal of 1445nm. The first reflecting surface 31 reflecting the light signal of 1445nm and the output coupler 52 are a third-order Raman fiber grating.

[0072] The first reflecting surface 31 reflecting 1276nm light signal, the second reflecting surface 51 reflecting 1276nm light signal and the Raman gain fiber 4 constitute an oscillation cavity. The first reflecting surface 31 reflecting 1276nm light signal and the second reflecting surface 51 reflecting 1276nm light signal are first order Raman fiber grating. The 1080nm light signal is converted to 1276nm by the Raman gain fiber 4, and is incident to the second reflecting surface 51 reflecting 1276nm light signal. The second reflecting surface 51 reflecting 1276nm light signal reflects the 1276nm light signal, which enters the Raman gain fiber 4. The Raman gain fiber 4 outputs 1363nm light signal, which is incident to the first reflecting surface reflecting 1363nm light signal. The first reflecting surface reflecting 1363nm light signal reflects the 1363nm light signal, which constitutes an oscillation cavity with the second reflecting surface reflecting 1363nm light signal. The first reflecting surface 31 reflecting 1363nm light signal and the second reflecting surface 51 reflecting 1363nm light signal are second order Raman fiber grating. The Raman gain fiber 4 outputs 1470nm light signal, which is incident to the first reflecting surface reflecting 1470nm light signal. The first reflecting surface reflecting 1470nm light signal constitutes an oscillation cavity with the output coupler 52. The output coupler 52 outputs 1470nm light signal. The first reflecting surface 31 reflecting 1470nm light signal and the output coupler 52 are third order Raman fiber grating.

[0073] Figure 11 A multi-stage Raman energy transfer schematic diagram is also provided. As shown in Figure 11 , 1080nm is converted to 1261nm, 1261nm is converted to 1345nm, 1345nm is converted to 1445nm, 1090nm is converted to 1276nm, 1276nm is converted to 1363nm, and 1363nm is converted to 1470nm. The frequency shift amount in the Raman energy transfer is shown in Figure 11 . Since the Raman gain fiber 4 is a phosphorus-doped fiber, the phosphorus-doped fiber has a relatively narrow gain peak near 1330cm -1 and 495cm -1 (see Figure 3 ). The wavelength selection is at the highest Raman gain position. Figure 11 The dashed arrows in -1 indicate energy cross transfer. The frequency shift amount from 1080nm to 1276nm is 1422cm -1 . The frequency shift amount from 1276nm to 1345nm is 402cm -1 . The frequency shift amount from 1345nm to 1470nm is 632cm -1 . The frequency shift amount from 1090nm to 1261nm is 1244cm -1The frequency shift from 1363 nm to 1445 nm is 416 cm -1 The frequency shift of the energy cross transfer is far away from the gain peak of the phosphorus-doped fiber (1330 cm -1 and 495 cm -1 Therefore, the wavelength will only shift to long wave along the intended path, and it is difficult to occur energy cross transfer.

[0074] Optionally, as shown in Figure 12 , the Raman fiber laser further comprises one or more of a controller 6, an isolator 7, a mode field adapter 8, or a plurality of reflectors 9, the functions of which are described above and will not be repeated here.

[0075] In an optional manner, as shown in Figure 7 and Figure 10 , the plurality of first reflecting surfaces 31 are implemented by Raman fiber gratings, and the second reflecting surface 51 and the output coupler 52 are both implemented by Raman fiber gratings.

[0076] In another optional manner, the plurality of first reflecting surfaces 31 are implemented by a film layer at the end surface of the fiber, and the second reflecting surface 51 and the output coupler 52 are both implemented by a film layer at the end surface of the fiber. For example, as shown in Figure 13 , the Raman gain fiber 4 is connected with a common fiber through a fiber connector, the film layer at the end surface of the fiber connector has high reflectivity for a plurality of specific wavelengths and high transmissivity for other wavelengths, in order to reduce loss, the film layer at the end surface is plated on the side close to the Raman gain fiber 4, without passing through the entire fiber connector. In this way, the film layer is used to implement the oscillation cavity, which can reduce cost and insertion loss.

[0077] Figure 14 The output spectrum of the Raman fiber laser is also provided. As shown in Figure 14 , the center wavelengths of the Raman laser are 1260 nm, 1276 nm, 1340 nm, 1360 nm, 1427 nm and 1445 nm respectively, and the powers of the light signals at the respective wavelengths are 731 mW, 1 W, 260 mW and 253 mW respectively after the respective wavelengths are separated by a wavelength division multiplexer and independently measured, and the overall optical efficiency is 11%.

[0078] The terms "first" and "second", and the like, used in the present application are used to distinguish between similar or identical items having substantially the same function and should be understood as not having a logical or chronological dependency between "first" and "second", nor limiting the number or the order of execution. It should also be understood that, although the following description uses the terms first, second, and the like to describe various elements, these elements should not be limited by the terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of various examples, a first reflecting surface can be referred to as a second reflecting surface, and similarly, a second reflecting surface can be referred to as a first reflecting surface. The first reflecting surface and the second reflecting surface can both be reflecting surfaces, and in some cases, can be separate and distinct reflecting surfaces.

[0079] The term "a plurality" in the present application means two or more.

[0080] The above description is only exemplary embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily think of various equivalent modifications or replacements within the scope of the technology disclosed in the present application, and these modifications or replacements should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A Raman fiber laser, characterized in that, It includes multiple pump optical components (1), a multiplexer (2), a multi-wavelength reflector (3), a Raman gain fiber (4), and a multi-wavelength output device (5); each of the multiple pump optical components (1) is connected to the multiplexer (2), the multiplexer (2) is connected to the multi-wavelength reflector (3), and the Raman gain fiber (4) is located between the multi-wavelength reflector (3) and the multi-wavelength output device (5); The plurality of pump optical components (1) are used to output optical signals of multiple wavelengths to the multiplexer (2); The multiplexer (2) is used to combine the optical signals of multiple wavelengths into a multiplexed signal and output it. The multi-wavelength reflector (3) is used to input the combined signal into the Raman gain fiber (4), reflect the intermediate Raman laser corresponding to each of the multiple wavelengths to perform Raman energy transfer, and reflect the target Raman laser corresponding to each wavelength. The multi-wavelength output device (5) is used to reflect the intermediate Raman laser corresponding to each wavelength for Raman energy transfer, and to output the target Raman laser corresponding to each wavelength.

2. The Raman fiber laser according to claim 1, characterized in that, The multi-wavelength reflector (3) includes multiple first reflective surfaces (31) corresponding to each wavelength, and the multi-wavelength output device (5) includes a second reflective surface (51) and an output coupler (52) corresponding to each wavelength. For the target wavelength among the multiple wavelengths, the number of first reflective surfaces (31) corresponding to the target wavelength is equal to the sum of the number of second reflective surfaces (51) and the number of output couplers (52). The multiple first reflecting surfaces (31) corresponding to the target wavelength are used to reflect the intermediate Raman laser and the target Raman laser output by the Raman gain fiber (4) corresponding to the target wavelength; The second reflecting surface (51) corresponding to the target wavelength is used to reflect the intermediate Raman laser corresponding to the target wavelength output by the Raman gain fiber (4); The output coupler (52) corresponding to the target wavelength is used to output the target Raman laser corresponding to the target wavelength.

3. The Raman fiber laser according to claim 2, characterized in that, The plurality of first reflecting surfaces (31) corresponding to each wavelength are implemented by Raman fiber gratings, and the second reflecting surface (51) and output coupler (52) corresponding to each wavelength are implemented by Raman fiber gratings; or, The plurality of first reflective surfaces (31) corresponding to each wavelength are realized by a film layer on the end face of the optical fiber, and the second reflective surface (51) and output coupler (52) corresponding to each wavelength are realized by a film layer on the end face of the optical fiber.

4. The Raman fiber laser according to any one of claims 1 to 3, characterized in that, The target Raman laser wavelength corresponding to each wavelength is between 1.4 μm and 1.5 μm; The Raman gain fiber (4) is a phosphorus-doped fiber; The Raman energy transfer in the Raman fiber laser depends on the 1330 cm⁻¹ of the phosphorus-doped fiber. -1 Gain peak at location.

5. The Raman fiber laser according to claim 4, characterized in that, The multiple wavelengths include a first wavelength and a second wavelength; The first wavelength and the second wavelength are between 1 μm and 1.1 μm, and the intermediate Raman laser corresponding to the first wavelength and the intermediate Raman laser corresponding to the second wavelength are between 1.2 μm and 1.3 μm.

6. The Raman fiber laser according to any one of claims 1 to 3, characterized in that, The target Raman laser wavelength corresponding to each wavelength of optical signal is between 1.4 μm and 1.5 μm; The Raman gain fiber (4) is a phosphorus-doped fiber; The Raman energy transfer in the Raman fiber laser depends on the 495 cm⁻¹ of the phosphorus-doped fiber. -1 and 1330cm -1 Gain peak at location.

7. The Raman fiber laser according to claim 6, characterized in that, The multiple wavelengths include a first wavelength and a second wavelength; The first wavelength and the second wavelength are between 1 μm and 1.1 μm. The two intermediate Raman lasers corresponding to the first wavelength are between 1.2 μm and 1.3 μm and between 1.3 μm and 14 μm, respectively. The two intermediate Raman lasers corresponding to the second wavelength are between 1.2 μm and 1.3 μm and between 1.3 μm and 14 μm, respectively.

8. The Raman fiber laser according to any one of claims 1 to 7, characterized in that, The Raman fiber laser also includes a controller (6); The controller (6) is connected to each of the pump optical components (1); The controller (6) is used to control the power of the optical signal output by each pump optical component (1) in order to control the power of the target Raman laser corresponding to each wavelength.

9. The Raman fiber laser according to any one of claims 1 to 8, characterized in that, Each pump optical component (1) includes a multimode pump optical module (11) and an oscillating cavity (12); The multimode pump light module (11) is used to input multimode pump light into the oscillation cavity (12); The oscillating cavity (12) is used to output an optical signal of a corresponding wavelength based on the multimode pump light.

10. The Raman fiber laser according to any one of claims 1 to 9, characterized in that, The Raman fiber laser also includes an isolator (7) and / or a mode field adapter (8); The isolator (7) and / or mode field adapter (8) are located in the optical path between the combiner (2) and the multi-wavelength reflector (3).

11. An optical amplifier, characterized in that, It includes gain fiber and Raman fiber laser as described in any one of claims 1 to 10.

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