A thulium-doped raman hybrid gain fiber laser

Abstract

The application discloses a thulium-doped Raman mixed gain fiber laser, which comprises a pump source, a signal laser module and a gain unit, the pump source outputs laser in an erbium wave band, the radiation wavelength range is 1530-1620 nm, and the signal laser module outputs laser in a cross band 1650-1800 nm of thulium-doped-Raman two kinds of gains, in the embodiment of the application, the thulium-doped Raman mixed gain fiber laser is used, the pump laser wave band output by the pump source is 1530-1620 nm, which is located in the absorption band of the thulium-doped fiber, the signal laser wave band output by the signal laser module is 1650-1800 nm, which is located in the cross band of the thulium-doped-Raman two kinds of gains, through the mixed gain of thulium doping and Raman, the output power of the signal laser and the pump-signal conversion efficiency are improved, under the double gain of thulium doping and Raman, most of the pump laser is converted into signal laser, and the higher power requirement of the 1.7 micron wave band signal laser can be met.

Description

Technical Field

[0001] The present invention relates to the technical field of lasers, and in particular to a thulium-doped Raman hybrid gain fiber laser. Background Art

[0002] Thulium-doped fibers have a very wide gain bandwidth, ranging from 1.7 microns to 2 microns. Fiber lasers in the 2-micron band have already achieved continuous optical output of hundreds of watts. However, in the 1.7-micron band, mature fiber lasers are limited to outputs of tens of watts. Both scientific research applications and industrial needs are increasingly demanding higher powers in this band.

[0003] The difficulty in achieving high power in this band is mainly due to its gain characteristics. Since the gain in this band is too weak, the conversion efficiency of pump laser to signal laser is too low. On the other hand, if the optical fiber is too long to provide sufficient gain, the 1.7-micron band will be reabsorbed by the gain fiber and converted into spontaneous radiation, affecting the output spectrum quality and making it difficult to increase the output power. Summary of the Invention

[0004] The present invention aims to solve one of the technical problems existing in the prior art.

[0005] The present application provides a thulium-doped Raman hybrid gain fiber laser capable of achieving dual gain and improving laser output power, comprising:

[0006] A pump source connected to the gain unit and used to output pump laser;

[0007] The gain unit is configured to receive the pump laser and trigger a gain mechanism through the pump laser;

[0008] a signal laser module, connected to the gain unit and coupled to the pump source, for inputting signal laser into the gain unit;

[0009] The pump laser has a wavelength of 1530-1620 nm, and the signal laser has a wavelength of 1650-1800 nm.

[0010] It is further defined that in the above-mentioned thulium-doped Raman hybrid gain fiber laser, the gain unit comprises a first gain fiber and a second gain fiber connected to the first gain fiber;

[0011] The first gain fiber is a thulium-doped fiber, and the second gain fiber is a Raman fiber with a length of ≥0 m.

[0012] It is further defined that the above-mentioned thulium-doped Raman hybrid gain fiber laser further includes:

[0013] A pump-signal optical combiner, used for coupling the pump laser and the signal laser together;

[0014] A pump light filter is used to separate the pump laser and the signal laser.

[0015] It is further defined that the above-mentioned thulium-doped Raman hybrid gain fiber laser, wherein the signal laser module includes:

[0016] A signal light source, configured to output the signal laser in the wavelength range of 1650-1800 nm;

[0017] The optical fiber isolator is used to receive the signal laser and output the signal laser to the gain unit, and prevent the signal light source from being affected by the reverse light from the reflection.

[0018] It is further defined that the above-mentioned thulium-doped Raman hybrid gain fiber laser, wherein the pump source and the output end of the optical fiber isolator are respectively connected to the input end of the pump-signal optical combiner, the output end of the pump-signal optical combiner is connected to the first gain fiber and the second gain fiber in sequence, and the output end of the second gain fiber is connected to the pump light filter.

[0019] It is further defined that the above-mentioned thulium-doped Raman hybrid gain fiber laser, wherein the output end of the optical fiber isolator is connected to the pump light filter, the pump light filter is connected to the first gain fiber and the second gain fiber in sequence, the second gain fiber is connected to the pump-signal combiner, and the pump-signal combiner is connected to the pump source.

[0020] Further defined, the above-mentioned thulium-doped Raman hybrid gain fiber laser, wherein the signal laser module includes a high-reflection grating and a low-reflection grating, wherein the high-reflection grating and the low-reflection grating are respectively connected to two ends of the gain unit and are used to provide feedback of the signal laser;

[0021] The central wavelength of the reflection of the high-reflection grating and the low-reflection grating is 1650-1800 nm.

[0022] It is further defined that the above-mentioned thulium-doped Raman hybrid gain fiber laser, wherein the pump source and the high-reflection grating are respectively connected to the input end of the pump-signal optical combiner, the output end of the pump-signal optical combiner is connected to the first gain fiber and the second gain fiber in sequence, the second gain fiber is connected to the low-reflection grating, and the low-reflection grating is connected to the pump light filter.

[0023] It is further defined that the above-mentioned thulium-doped Raman hybrid gain fiber laser, wherein the high-reflection grating is connected to the pump light filter, the pump light filter is connected to the first gain fiber and the second gain fiber in sequence, the second gain fiber is connected to the low-reflection grating, the low-reflection grating is connected to the pump-signal light combiner, and the pump-signal combiner is connected to the pump source.

[0024] The present invention has the following beneficial effects:

[0025] The pump laser output by the pump source has a wavelength band of 1530-1620nm, which is within the absorption band of thulium-doped fiber. The signal laser output by the signal laser module has a wavelength band of 1650-1800nm, which is within the cross-band of thulium-doped and Raman gains. Through the mixed gain of thulium and Raman, the output power of the signal laser and the pump-signal conversion efficiency are improved. Under the dual gain of thulium and Raman, most of the pump laser is converted into signal laser, which can meet the higher power requirements of the 1.7-micron band signal laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the structure of the thulium-doped Raman hybrid gain fiber laser in Example 2 of the present application;

[0027] Figure 2 Schematic diagram of the structure of the thulium-doped Raman hybrid gain fiber laser in Example 3 of the present application;

[0028] Figure 3 Schematic diagram of the structure of the thulium-doped Raman hybrid gain fiber laser in Example 4 of the present application;

[0029] Figure 4 Schematic diagram of the structure of the thulium-doped Raman hybrid gain fiber laser in Example 5 of the present application;

[0030] Figure 5 is a typical Raman gain spectrum.

[0031] Reference numerals

[0032] Signal light source 110, fiber isolator 120, high-reflection grating 130, low-reflection grating 140, pump source 200, pump-signal light combiner 300, first gain fiber 410, second gain fiber 420, pump light filter 500. DETAILED DESCRIPTION

[0033] The following will be combined with the accompanying drawings in the embodiments of the present application to clearly describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of this application.

[0034] The terms "first," "second," and the like in the specification and claims of this application are used to distinguish similar objects, and are not used to describe a specific order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of this application can be implemented in an order other than that illustrated or described herein, and that the objects distinguished by "first," "second," and the like are generally of the same type, and do not limit the number of objects; for example, the first object can be one or more. In addition, the term "and / or" in the specification and claims refers to at least one of the connected objects, and the character " / " generally indicates that the objects connected are in an "or" relationship.

[0035] The thulium-doped Raman hybrid gain fiber laser provided in the embodiments of the present application is described in detail below through specific embodiments and application scenarios in conjunction with the accompanying drawings.

[0036] Example 1:

[0037] like Figures 1 to 4 As shown, an embodiment of the present application provides a thulium-doped Raman hybrid gain fiber laser, including a pump source 200, a signal laser module, and a gain unit. The pump source 200 is connected to the gain unit to trigger the gain mechanism of the gain unit. The signal laser module is connected to the gain unit and coupled to the pump source 200 to input a signal laser of a fixed band into the gain unit. The gain unit includes a first gain fiber 410 and a second gain fiber 420 connected in sequence. The first gain fiber 410 is a thulium-doped fiber, preferably a thulium-doped fiber with a high Raman gain coefficient. The second gain fiber 420 is a Raman fiber. Since any optical fiber can provide Raman gain, when the Raman gain of the first gain fiber 410 is sufficient, the second gain fiber 420 may not be required. Therefore, the length of the second gain fiber 420 is specified to be ≥0m.

[0038] The pump source 200 is an erbium-band laser with a radiation wavelength generally between 1530 and 1620 nm. This wavelength is within the absorption band of thulium-doped fiber, and gain can be provided by thulium-doped fiber. This wavelength is used as a pump laser, and the Stokes laser wavelength generated by Raman gain is calculated as follows:

[0039]

[0040] Where Δυ is the wave number corresponding to the Raman peak gain, λ p is the pump light wavelength, λs is the Stokes wavelength. In conventional Raman optical fibers, the wave number Δυ corresponding to the Raman peak gain is usually 400 cm -1 In fact, the entire Raman gain is very wide, Figure 5 It can be estimated that the gain range can reach 167-667cm -1 According to the above formula, the Stokes wavelength can cover around 1640-1800nm, the Raman gain band covers 1640-1800nm, and the gain range of thulium-doped fiber can cover around 1650-2000nm. The overlapping gain part of the two is the operating wavelength designed for our laser.

[0041] That is, the wavelength band of the pump source 200 is 1530-1620 nm, and the wavelength band of the laser output by the signal laser module is the cross band of 1650-1800 nm of the two gains of thulium-doped and Raman.

[0042] It also includes a pump-signal optical combiner 300 and a pump light filter 500 connected to the pump source 200, the signal laser module, and the gain unit. The pump-signal optical combiner 300 is used to couple the pump laser and the signal laser together. It can be a conventional signal light-cladding optical combiner or a wavelength division multiplexer, etc. The pump light filter 500 is used to separate the pump laser and the signal laser. When the system selects cladding pumping, it can be a cladding light filter. When the system selects core pumping, it can be a wavelength division multiplexer.

[0043] In an embodiment of the present application, the above-mentioned thulium-doped Raman hybrid gain fiber laser is used, and the pump laser band output by the pump source 200 is 1530-1620nm, which is located in the absorption band of the thulium-doped fiber. The signal laser band output by the signal laser module is 1650-1800nm, which is located in the cross-band of the thulium-doped and Raman gains. Through the hybrid gain of thulium doping and Raman, the output power of the signal laser and the pump-signal conversion efficiency are improved. Under the dual gain of thulium doping and Raman, most of the pump laser is converted into signal laser, which can meet the higher power requirements of the 1.7-micron band signal laser.

[0044] Example 2:

[0045] like Figure 1As shown, in this embodiment, the structure of the present invention is a fiber amplifier, including the structural features of the aforementioned embodiment 1, wherein the signal laser module includes a signal light source 110 and a fiber isolator 120. The signal light source 110 is used to output a signal laser with a wavelength band of 1650-1800nm. The fiber isolator 120 is connected to the signal laser output end of the signal light source 110 to protect the signal light source 110, prevent the signal light source 110 from being affected by the reverse light from the reflection and causing its spectral purity to decrease, and improve the working stability of the signal light source 110.

[0046] The output ends of the pump source 200 and the optical fiber isolator 120 are respectively connected to the input end of the pump-signal optical combiner 300. The output end of the pump-signal optical combiner 300 is connected to the first gain fiber 410 and the second gain fiber 420 in sequence. The output end of the second gain fiber 420 is connected to the pump light filter 500.

[0047] At this time, the laser is in the forward pumping state. The signal laser output by the signal light source 110 passes through the optical fiber isolator 120 and is combined with the pump laser output by the pump source 200 through the pump-signal combiner. The combined laser is injected into the first gain fiber 410. Under the pumping of the pump laser, the first optical fiber provides gain to amplify the signal laser. When passing through the second gain fiber 420, the remaining pump laser amplifies the signal laser through Raman gain. Finally, the amplified signal laser and the remaining pump laser are separated by the pump light filter 500, and the high-power signal laser is output optically.

[0048] In an embodiment of the present application, in a high-power, high-efficiency 1710nm laser system pumped by a 1590nm laser using the above-mentioned solution, the signal laser output by the laser light source is a single-frequency signal of 1710nm, the pump laser output by the pump source 200 is 1590nm, the pump-signal combiner is specifically a first 1710 / 1590 polarization-maintaining WDM, the pump light filter 500 is specifically a second 1710 / 1590 polarization-maintaining WDM, and the 1710nm signal laser passes through the optical fiber isolator 120 and is coupled into the first gain fiber 410 through the first 1710 / 1590 polarization-maintaining WDM and the 1590nm pump laser. Here, the first gain fiber 410 is specifically a Raman A TDF-4 / 125 optical fiber with a large gain coefficient is used. A second gain fiber 420 is fused behind the first gain fiber 410. The second gain fiber 420 is specifically a highly nonlinear optical fiber. Under the pumping of a 1590nm pump laser, the first gain fiber 410 provides rare earth ion gain and Raman gain, and the second gain fiber 420 provides higher Raman gain. In order to suppress possible stimulated Brillouin scattering, a certain gradient of stress is applied to the second gain fiber 420. Ultimately, under dual gain, most of the pump laser is converted into signal laser, and a small part of the pump laser is separated from the system through the second 1710 / 1590 polarization-maintaining WDM, and a high-power 1710nm signal laser is output.

[0049] Example 3:

[0050] like Figure 2 As shown, in this embodiment, the structure of the present invention is a fiber amplifier, including the structural features of the aforementioned embodiment 1, wherein the signal laser module includes a signal light source 110 and a fiber isolator 120. The signal light source 110 is used to output a signal laser with a wavelength band of 1650-1800nm. The fiber isolator 120 is connected to the signal laser output end of the signal light source 110 to protect the signal light source 110, prevent the signal light source 110 from being affected by the reverse light from the reflection and causing its spectral purity to decrease, and improve the working stability of the signal light source 110.

[0051] The output end of the optical fiber isolator 120 is connected to the pump light filter 500 , which is sequentially connected to the first gain fiber 410 and the second gain fiber 420 . The second gain fiber 420 is connected to the pump-signal combiner, which is connected to the pump source 200 .

[0052] At this time, the laser is in a backward pumping state. The signal laser output by the signal light source 110 is injected into the first gain fiber 410 and the second gain fiber 420 through the fiber isolator 120 and the pump light filter 500 for forward transmission. The pump laser output by the pump source 200 is coupled into the system through the pump-signal combiner. The pump laser and the signal laser meet in the gain unit. The signal laser is amplified and output through the pump-signal combiner. The remaining pump laser is completely absorbed or output from the system through the pump light filter 500.

[0053] Example 4:

[0054] like Figure 3 As shown, in this embodiment, the structure of the present invention is a fiber oscillator, including the structural features of the aforementioned embodiment 1, wherein the signal laser module includes a high-reflection grating 130 and a low-reflection grating 140, and the high-reflection grating 130 and the low-reflection grating 140 are respectively connected to the two ends of the gain unit. The high-reflection grating 130 and the low-reflection grating 140 are fiber Bragg gratings, and the central wavelength of the reflection is about 1650-1800nm, which are used to provide feedback of the signal laser and select the longitudinal mode, that is, the oscillation mode. The reflectivity of the low-reflection grating 140 is lower than that of the high-reflection grating 130.

[0055] The pump source 200 and the high-reflection grating 130 are respectively connected to the input end of the pump-signal optical combiner 300. The output end of the pump-signal optical combiner 300 is connected to the first gain fiber 410 and the second gain fiber 420 in sequence. The second gain fiber 420 is connected to the low-reflection grating 140, and the low-reflection grating 140 is connected to the pump light filter 500.

[0056] At this time, the laser is in a forward pumping state. The pump laser output by the pump source 200 is coupled into the system through the pump-signal combiner. Under the action of the pump laser, the gain unit triggers a gain mechanism. The low-reflection grating 140 receives the pump laser and reflects and outputs a signal laser with a central wavelength of 1650-1800nm. The signal laser is amplified by the gain unit, and the signal laser is fed back and forth between the low-reflection grating 140 and the high-reflection grating 130. This reciprocating feedback amplification of the signal laser is achieved. The power-amplified signal laser is output by the low-reflection grating 140 through the pump light filter 500. At the same time, the pump light filter 500 separates the signal laser from the residual pump laser.

[0057] Example 5:

[0058] like Figure 4As shown, in this embodiment, the structure of the present invention is a fiber oscillator, including the structural features of the aforementioned embodiment 1. The signal laser module includes a high-reflection grating 130 and a low-reflection grating 140, respectively connected to the two ends of the gain unit. High-reflection grating 130 and low-reflection grating 140 are fiber Bragg gratings (FBGs) with a central reflection wavelength of approximately 1650-1800 nm. They provide feedback for the signal laser and select the longitudinal mode, i.e., the oscillation mode. The low-reflection grating 140 has a lower reflectivity than the high-reflection grating 130.

[0059] The high-reflection grating 130 is connected to the pump light filter 500, the pump light filter 500 is connected to the first gain fiber 410 and the second gain fiber 420 in sequence, the second gain fiber 420 is connected to the low-reflection grating 140, the low-reflection grating 140 is connected to the pump-signal light combiner 300, and the pump-signal light combiner is connected to the pump source 200.

[0060] At this time, the laser is in a backward pumping state. The pump laser output by the pump source 200 is coupled into the system through the pump-signal combiner. Under the action of the pump laser, the gain unit triggers a gain mechanism. The low-reflection grating 140 receives the pump laser and reflects and outputs a signal laser with a central wavelength of 1650-1800nm. The signal laser is amplified by the gain unit, and the signal laser is fed back and forth between the low-reflection grating 140 and the high-reflection grating 130. This reciprocating feedback amplification of the signal laser is achieved. The power-amplified signal laser is output by the low-reflection grating 140 through the pump-signal combiner. At the same time, the remaining pump laser is completely absorbed or guided out of the system through the pump light filter 500.

[0061] It should be noted that, in this article, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element. In addition, it should be noted that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in the opposite order according to the functions involved. For example, the described method may be performed in an order different from that described, and various steps may also be added, omitted, or combined. In addition, the features described with reference to certain examples may be combined in other examples.

[0062] The embodiments of the present application are described above with reference to the accompanying drawings, but the present application is not limited to the specific embodiments described above, and the specific embodiments described above are merely illustrative, but not restrictive, and a person of ordinary skill in the art can make many forms under the inspiration of the present application without departing from the purpose of the present application and the scope protected by the claims.

Claims

1. A thulium-doped Raman hybrid gain fiber laser, characterized in that: include: A pump source connected to the gain unit and used to output pump laser; The gain unit is configured to receive the pump laser and trigger a gain mechanism through the pump laser; the gain unit comprises a first gain fiber and a second gain fiber connected to the first gain fiber; Wherein, the first gain fiber is a thulium-doped fiber, and the second gain fiber is a Raman fiber with a length ≥ 0m; a signal laser module, connected to the gain unit and coupled to the pump source, for inputting signal laser into the gain unit; The pump laser has a wavelength of 1530-1620 nm, and the signal laser has a wavelength of 1650-1800 nm.

2. The thulium-doped Raman hybrid gain fiber laser according to claim 1, characterized in that: Also includes: A pump-signal optical combiner, used for coupling the pump laser and the signal laser together; A pump light filter is used to separate the pump laser and the signal laser.

3. The thulium-doped Raman hybrid gain fiber laser according to claim 2, characterized in that: The signal laser module includes: A signal light source, configured to output the signal laser in the wavelength range of 1650-1800 nm; The optical fiber isolator is used to receive the signal laser and output the signal laser to the gain unit, and prevent the signal light source from being affected by the reverse light from the reflection.

4. The thulium-doped Raman hybrid gain fiber laser according to claim 3, characterized in that: The pump source and the output end of the optical fiber isolator are respectively connected to the input end of the pump-signal optical combiner. The output end of the pump-signal optical combiner is sequentially connected to the first gain optical fiber and the second gain optical fiber. The output end of the second gain optical fiber is connected to the pump light filter.

5. The thulium-doped Raman hybrid gain fiber laser according to claim 3, characterized in that: The output end of the optical fiber isolator is connected to the pump light filter, the pump light filter is connected to the first gain fiber and the second gain fiber in sequence, the second gain fiber is connected to the pump-signal combiner, and the pump-signal combiner is connected to the pump source.

6. The thulium-doped Raman hybrid gain fiber laser according to claim 2, characterized in that: The signal laser module includes a high-reflection grating and a low-reflection grating, which are respectively connected to the two ends of the gain unit and are used to provide feedback of the signal laser; wherein the central wavelength of the reflection of the high-reflection grating and the low-reflection grating is 1650-1800nm.

7. The thulium-doped Raman hybrid gain fiber laser according to claim 6, characterized in that: The pump source and the high-reflection grating are respectively connected to the input end of the pump-signal optical combiner, and the output end of the pump-signal optical combiner is connected to the first gain fiber and the second gain fiber in sequence. The second gain fiber is connected to the low-reflection grating, and the low-reflection grating is connected to the pump light filter.

8. The thulium-doped Raman hybrid gain fiber laser according to claim 6, characterized in that: The high-reflection grating is connected to the pump light filter, the pump light filter is connected to the first gain fiber and the second gain fiber in sequence, the second gain fiber is connected to the low-reflection grating, the low-reflection grating is connected to the pump-signal light combiner, and the pump-signal light combiner is connected to the pump source.

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