Continuous fiber laser

Abstract

The invention discloses a continuous optical fiber laser, and relates to the technical field of lasers, the continuous optical fiber laser comprises an output device, a first stripper, a first beam combiner, a composite resonant cavity, a second beam combiner and a second stripper which are sequentially connected through a central fiber, the composite resonant cavity is internally provided with a plurality of sub-cavities, and the sub-cavities are used for filtering and enhancing laser beams; the continuous fiber laser further comprises a plurality of first pumping sources and a plurality of second pumping sources, wherein the plurality of first pumping sources are respectively connected with the first beam combiner; and the plurality of second pumping sources are respectively connected with the second beam combiner. According to the technical scheme, the overall structure is simple, and low-cost and high-efficiency suppression of the nonlinear effect is achieved only through cooperation of the output device, the stripper and the beam combiner.

Description

Technical Field

[0001] The invention relates to the technical field of lasers, and in particular to a continuous fiber laser. Background Art

[0002] Continuous fiber lasers are widely used in industry and scientific research due to their high power, high stability and compactness. They have significant advantages in practical engineering applications and on space-constrained payload platforms, and are ideal sub-beam modules for high-power spectrum synthesis.

[0003] The central wavelength and spectral line width of high-power narrow-linewidth fiber lasers are mainly determined by the characteristics of the seed source. Affected by the self-pulsation effect, when the power of the multi-longitudinal mode oscillation seed source laser is amplified to several kilowatts, it manifests itself in the spectrum as the broadening of the laser peak and the enhancement of the Raman peak. The problem of laser spectral purity degradation has brought about adverse effects such as reduced efficiency, increased stray light, and deteriorated beam quality in subsequent spectral beam combining applications.

[0004] The optical power density in the optical fiber is high, and various nonlinear effects such as stimulated Brillouin scattering (SBS), self-phase modulation (SPM), four-wave mixing (FWM), and stimulated Raman scattering (SRS) are very likely to occur during the laser amplification process. In the prior art, the methods for suppressing these nonlinear effects are inefficient or too costly. Summary of the invention

[0005] The main purpose of the present invention is to provide a continuous fiber laser, aiming to solve the technical problem that the method of suppressing nonlinear effects in the prior art is inefficient or too costly.

[0006] To achieve the above object, the present invention provides a continuous fiber laser, which includes an output device, a first stripper, a first beam combiner, a composite resonant cavity, a second beam combiner, and a second stripper connected in sequence through a central fiber, wherein the composite resonant cavity has a plurality of sub-cavities, and the sub-cavities are used to filter and enhance the laser beam;

[0007] The continuous fiber laser also includes:

[0008] A plurality of first pump sources, wherein the plurality of first pump sources are respectively connected to the first beam combiner;

[0009] A plurality of second pump sources are respectively connected to the second beam combiner.

[0010] In one embodiment, the composite resonant cavity comprises:

[0011] A plurality of fiber gratings, wherein the plurality of fiber gratings are connected in sequence;

[0012] An active optical fiber is arranged between any two adjacent fiber gratings, wherein all the fiber gratings on one side of the active optical fiber and any one of the fiber gratings on the other side of the active optical fiber form a sub-cavity.

[0013] In one embodiment, there are multiple active optical fibers, and the multiple active optical fibers and the multiple fiber gratings are arranged in sequence and spaced apart, wherein any two of the fiber gratings form one sub-cavity.

[0014] In one embodiment, the active optical fiber comprises Yb 3+ , Er 3+ 、Tm 3+ 、Ho 3+ 、Dy 3+ One or more doping compositions.

[0015] In one embodiment, the fiber Bragg grating is manufactured by a hydrogen-loaded mask lithography process, and the reflectivity of the fiber Bragg grating is 10% to 99.5%.

[0016] In one embodiment, the wavelength filtering range of the composite resonant cavity is 1030 nm to 2020 nm.

[0017] In one embodiment, an end cap is provided on the output end of the output device, an anti-reflection film is provided on the end cap, and a roughened area is provided inside the output device.

[0018] In one embodiment, an end of the second stripper facing away from the second combiner has a bevel angle, and the angle of the bevel angle is 6° to 10°.

[0019] In one embodiment, the first beam combiner is a forward beam combiner, and the plurality of first pump sources are respectively connected to one end of the first beam combiner toward the first stripper through pump fibers;

[0020] The second beam combiner is a reverse beam combiner, and a plurality of the second pump sources are respectively connected to one end of the second beam combiner facing the second stripper through pump fibers.

[0021] In one embodiment, the signal-to-noise ratio of the composite resonant cavity is 0.06-0.1.

[0022] The technical solution of the present invention adds the composite resonant cavity to the optical path structure, and the nonlinear suppression technology of the continuous fiber laser. The composite resonant cavity includes a plurality of sub-cavities. The oscillation longitudinal mode of a single sub-cavity is greatly affected by the thermal effect, which will induce continuous parasitic oscillation and aggravate the self-pulsation of the pump source. After the composite resonant cavity is formed, the oscillation longitudinal mode needs to simultaneously satisfy the resonant structure of a plurality of sub-cavities, which is conducive to stabilizing the oscillation frequency and filtering out unnecessary nonlinear spectral components. The overall structure is simple, and only by coordinating the output device, the stripper, and the combiner, the nonlinear effect can be suppressed at low cost and high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0024] Figure 1 A schematic diagram of the structure of a continuous fiber laser provided by the present invention;

[0025] Figure 2 A schematic structural diagram of a first embodiment of a composite resonant cavity in a continuous fiber laser provided by the present invention;

[0026] Figure 3 A schematic structural diagram of a second embodiment of a composite resonant cavity in a continuous fiber laser provided by the present invention;

[0027] Figure 4 A schematic structural diagram of a third embodiment of a composite resonant cavity in a continuous fiber laser provided by the present invention;

[0028] Figure 5 a in the figure is a self-pulsation spectrum test result diagram of the continuous fiber laser of the present invention without using a composite resonant cavity mode;

[0029] Figure 5 b is a graph showing the self-pulsation spectrum test result of the continuous fiber laser of the present invention using a composite resonant cavity;

[0030] Figure 6 This is a characteristic spectrum test diagram of the nonlinear effect of the continuous fiber laser of the present invention.

[0031] Description of Figure Numbers:

[0032] 10. Output device; 11. End cap; 20. First stripper; 30. First beam combiner; 40. Second beam combiner; 50. Second stripper; 61. First pump source; 62. Second pump source; 70. Composite resonant cavity; 71. Fiber Bragg grating; 72. Active optical fiber.

[0033] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components in a certain specific posture. If the specific posture changes, the directional indication will also change accordingly.

[0036] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features limited to "first" and "second" may explicitly or implicitly include at least one of the features. In addition, if "and / or" or "and / or" appears in the full text, its meaning includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, solution B, or solutions that satisfy both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0037] The present invention provides a continuous fiber laser.

[0038] See also Figure 1In one embodiment of the present invention, the continuous fiber laser includes an output device 10, a first stripper 20, a first beam combiner 30, a composite resonant cavity 70, a second beam combiner 40, and a second stripper 50 connected in sequence through a central fiber, wherein the composite resonant cavity 70 has a plurality of sub-cavities, and the sub-cavities are used to filter and enhance the laser beam; the continuous fiber laser also includes: a plurality of first pump sources 61 and a plurality of second pump sources 62, wherein the plurality of first pump sources 61 are respectively connected to the first beam combiner 30; and the plurality of second pump sources 62 are respectively connected to the second beam combiner 40.

[0039] In the optical path, the light beam is emitted from the laser after passing through each optical element. The direction in which the laser is emitted from the laser in the optical path is generally defined as the forward direction of the optical path. In the optical path of the same optical structure, along the forward direction of each optical element, the side where the light beam is emitted is the first end, and the side where the light beam enters is the second end.

[0040] See also Figure 1 , from right to left are the output device 10, the first stripper 20, the first combiner 30, the composite resonant cavity 70, the second combiner 40, and the second stripper 50.

[0041] A central fiber runs through the output device 10, the first stripper 20, the first combiner 30, the composite resonant cavity 70, the second combiner 40, and the second stripper 50, and the direction of the optical path from left to right is the positive direction.

[0042] The right side of the output device 10, the first stripper 20, the first combiner 30, the composite resonant cavity 70, the second combiner 40, and the second stripper 50 is the first end, and the left side of the output device 10, the first stripper 20, the first combiner 30, the composite resonant cavity 70, the second combiner 40, and the second stripper 50 is the second end.

[0043] The plurality of first pump sources 61 are connected to the first end of the first beam combiner 30 through an independent pump fiber, respectively. The plurality of second pump sources 62 are connected to the second end of the second beam combiner 40 through an independent pump fiber, respectively.

[0044] The pump source provides a light beam, which is injected into the composite resonant cavity 70 through the pump fiber. The light beam continuously passes through the sub-cavities in the composite resonant cavity 70, and is filtered and enhanced by the sub-cavities, and finally forms a laser beam and is emitted from the output device 10.

[0045] Among them, see Figure 1The first combiner 30 is a forward combiner, and multiple first pump sources 61 are respectively connected to one end of the first combiner 30 toward the first stripper 20 through pump fibers; the second combiner 40 is a reverse combiner, and multiple second pump sources 62 are respectively connected to one end of the second combiner 40 toward the second stripper 50 through pump fibers.

[0046] The first pump source 61 is a forward pump source, and the second pump source 62 is a reverse pump source. The two pumping modes can be used alone or in combination.

[0047] Correspondingly, the first combiner 30 is a forward combiner, and multiple first pump sources 61 are respectively connected to one end of the first combiner 30 toward the first stripper 20 through pump fibers; the second combiner 40 is a reverse combiner, and multiple second pump sources 62 are respectively connected to one end of the second combiner 40 toward the second stripper 50 through pump fibers.

[0048] The beam combiners can all be (N+1)*1 type beam combiners, such as (6+1)*1 beam combiners, and the number of first pump sources 61 is 6. Figure 1 The left side of the first combiner 30 is a combining end, which is connected to the composite resonant cavity 70 , and the right side is a branching end, one of which is connected to the first stripper 20 through the central fiber, and the other branches are connected to a first pump source 61 .

[0049] Similarly, the second beam combiner 40 has a similar structure to the first beam combiner 30 but in the opposite direction, using a (6+1)*1 beam combiner, and the number of the second pump sources 62 is also 6. Figure 1 That is, the left side of the second combiner 40 is a branching end, and the right side is a combining end.

[0050] Furthermore, in this embodiment, a second stripper 50 is provided on the leftmost side of the pipeline, and a first stripper 20 is provided between the output device 10 and the first combiner 30 .

[0051] The stripper can adopt a passive optical fiber of 50 / 400 / 0.12 (core diameter / cladding diameter / numerical aperture), obtained by CO2 laser etching, and is used to efficiently strip the cladding light from forward transmission or reverse transmission, with a cladding light stripping rate of about 20dB.

[0052] The technical solution of the present invention adds the composite resonant cavity 70 to the optical path structure, and the nonlinear suppression technology of the continuous fiber laser. The composite resonant cavity 70 includes a plurality of sub-cavities. The oscillation longitudinal mode of a single sub-cavity is greatly affected by the thermal effect, which will induce continuous parasitic oscillation and aggravate the self-pulsation of the pump source. After the composite resonant cavity 70 is formed, the oscillation longitudinal mode needs to simultaneously meet the resonant structure of a plurality of sub-cavities, which is conducive to stabilizing the oscillation frequency and filtering out unnecessary nonlinear spectral components. The overall structure is simple, and only by cooperating with the output device 10, the stripper, and the combiner, the nonlinear effect can be suppressed at low cost and high efficiency.

[0053] In one embodiment, the composite resonant cavity 70 includes a plurality of sub-cavities. The oscillation longitudinal mode of a single sub-cavity is greatly affected by the thermal effect, which will induce continuous parasitic oscillation and aggravate the self-pulsation of the pump source. After the composite resonant cavity 70 is formed, the oscillation longitudinal mode needs to simultaneously meet the resonant structure of the plurality of sub-cavities, which is conducive to stabilizing the oscillation frequency and filtering out the redundant nonlinear spectral components. The overall structure is simple, and only by coordinating the output device 10, the stripper, and the beam combiner, the nonlinear effect can be suppressed at low cost and high efficiency.

[0054] In this embodiment, the active optical fiber 72 can be a high-gain doped active optical fiber 72. It is a high-gain rare-earth doped optical fiber, the composition of which includes Yb 3+ , Er 3+ 、Tm 3+ 、Ho 3+ or Dy 3+ The composition can be single-doped with at least one component, double-doped with two components, or multi-doped with more than two components.

[0055] For example, the structural parameters of the active optical fiber 72 may be 20 / 400 / 0.065, the absorption coefficient may be about 0.38 dB / m, and the length may be greater than or equal to 40 m.

[0056] In this embodiment, the fiber Bragg grating 71 can be obtained by using a hydrogen-carrying mask lithography process. In this embodiment, the central wavelength of the fiber Bragg grating 71 can be set within the range of 1030nm to 2020nm, so that the wavelength filtering range of the composite resonant cavity 70 is 1030nm to 2020nm. The reflectivity of the fiber Bragg grating 71 is in the range of 10% to 99.5%.

[0057] A plurality of fiber gratings 71 are arranged at intervals, and the position of the active optical fiber 72 is adjusted, so that a plurality of fiber gratings 71 and the active optical fiber 72 are combined to form different sub-cavities.

[0058] See also Figure 2In this embodiment, multiple fiber gratings 71 are arranged from left to right, namely a1, a2, a3, a4, a5, a6..., and the active optical fiber 72 is arranged on the left optical path of the a6th fiber grating 71 and connected to the a6th fiber grating 71.

[0059] Among them, a1 and a6 form the first sub-cavity, a1 and a6 are used to reflect the light beam emitted from the pump source, and the light beam frequently passes through the active optical fiber 72 between a1 and a6, thereby achieving laser enhancement. Finally, the central wavelength of the fiber grating 71 is met and output to the output device 10 by the central fiber.

[0060] Similarly, a2 and a6 form the second sub-cavity, a3 and a6 form the third sub-cavity, and so on. When the number of fiber gratings 71 is greater, the number of sub-cavities formed is greater. The greater the number of fiber gratings 71, the greater the screening accuracy of the laser can be improved, so that only the laser with a wavelength within the set value range can be emitted. In this embodiment, the wavelength range is 1030nm to 2020nm as an example.

[0061] As another embodiment, the position of the active optical fiber 72 can be adjusted. Figure 3 , the active optical fiber 72 can be arranged between a1 and a2, then a first sub-cavity is formed between a1 and a2, a second sub-cavity is formed between a1 and a3, a third sub-cavity is formed between a1 and a4, and so on.

[0062] As another embodiment, there are multiple active optical fibers 72 , and the multiple active optical fibers 72 and the multiple fiber gratings 71 are arranged in sequence and spaced apart from each other, wherein any two of the fiber gratings 71 form one sub-cavity.

[0063] See also Figure 4 By increasing the number of active optical fibers 72, an active optical fiber 72 is arranged between every two adjacent fiber gratings 71, and in this embodiment, a sub-cavity can be formed between any two fiber gratings 71. Then, the number of sub-cavities formed is further increased, and the efficiency is improved.

[0064] In addition, in this embodiment, the intensity of the laser light can be increased by increasing the length of the active optical fiber 72 .

[0065] In one embodiment, an end cap 11 is provided on the output end of the output device 10 , an anti-reflection film is provided on the end cap 11 , and a roughened area is provided inside the output device 10 .

[0066] In this embodiment, the optical fiber type of the output device 10 is 50 / 400 / 0.12 passive optical fiber, see Figure 1The output end of the output device 10 is the right end, and the output end is welded to the quartz end cap 11 coated with an anti-reflection film. There is a roughened area inside the output device 10 obtained by corrosive abrasive corrosion or CO2 laser etching process to achieve forward cladding light stripping and reverse return cladding light stripping.

[0067] The light of the first pump source 61 and / or the second pump source 62 is generated by a semiconductor and output through optical fiber coupling. In this embodiment, the light output wavelength of the pump source is 915 nm, the output power of the pump source is ≥ 650 W, and the output pigtail is 200 / 220 / 0.22.

[0068] By modulating the injection current of the pump source, pump light with different powers can be injected into the composite resonant cavity 70, and finally the composite resonant cavity 70 is used to output a continuous 1080nm laser.

[0069] The central wavelength of the fiber grating 71 is in the range of 1030-2020nm, and its spectral bandwidth is in the range of 1nm-4nm. In this embodiment, the central wavelength of 1080nm and the spectral bandwidth of 3nm are taken as an example for explanation, and the reflectivity of the fiber grating 71 is 10%-99.5%.

[0070] By modulating the light injected into the pump source, the laser can achieve a 1080nm fiber laser output with a high peak power of more than 2500W.

[0071] Furthermore, as an embodiment, the above parameters are used for actual demonstration. Figure 5 a in the figure is a self-pulsation spectrum test result diagram of the continuous fiber laser of the present invention without using the composite resonant cavity 70. Figure 5 FIG. b is a graph showing the self-pulsation spectrum test result of the continuous fiber laser of the present invention using the composite resonant cavity 70. FIG.

[0072] At 10A current, Figure 5 When the composite resonant cavity 70 is not used but the common cavity structure is used, the signal-to-noise ratio is 0.18; Figure 5 When the composite resonant cavity 70 is used, the signal-to-noise ratio is 0.06. This proves that in the composite resonant cavity 70 structure, the self-pulsation effect of the seed source is suppressed, thereby achieving the purpose of improving the nonlinear threshold.

[0073] For further information, see Figure 6 , Figure 6This is a characteristic spectrum test diagram of the nonlinear effect of the continuous fiber laser of the present invention. It can be seen from the figure that when the composite resonant cavity 70 is not used and the ordinary cavity structure is used, when the pump source power is 2636W, the Raman peak and the laser main peak intensity differ by only 10dB; when the composite resonant cavity 70 is used and the pump source power is 3180W, no Raman peak spectrum is observed, thereby achieving the suppression of nonlinear effects.

[0074] In one embodiment, the end of the second stripper 50 away from the second beam combiner 40 has a bevel angle, and the angle of the bevel angle is 6° to 10°. The left end of the second stripper 50 is the output end, and a bevel angle is used on the left side of its end face to prevent the light beam reflected by the end face from affecting the internal optical path and reducing the laser quality. The angle of the bevel angle can be 8°.

[0075] The above description is only an exemplary embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A continuous fiber laser, characterized in that: The continuous fiber laser comprises an output device, a first stripper, a first beam combiner, a composite resonant cavity, a second beam combiner, and a second stripper which are sequentially connected through a central fiber. The composite resonant cavity has a plurality of sub-cavities, and the sub-cavities are used to filter and enhance the laser beam. The continuous fiber laser also includes: A plurality of first pump sources, wherein the plurality of first pump sources are respectively connected to the first beam combiner; A plurality of second pump sources are respectively connected to the second beam combiner.

2. The continuous fiber laser according to claim 1, characterized in that The composite resonant cavity comprises: A plurality of fiber gratings, wherein the plurality of fiber gratings are connected in sequence; An active optical fiber is arranged between any two adjacent fiber gratings, wherein all the fiber gratings on one side of the active optical fiber and any one of the fiber gratings on the other side of the active optical fiber form a sub-cavity.

3. The continuous fiber laser according to claim 2, characterized in that: There are multiple active optical fibers, and the multiple active optical fibers and the multiple fiber gratings are arranged in sequence and spaced apart, wherein any two of the fiber gratings form one sub-cavity.

4. The continuous fiber laser according to claim 2, characterized in that: The active optical fiber includes Yb 3+ , Er 3+ 、Tm 3 + 、Ho 3+ 、Dy 3+ One or more doping compositions.

5. The continuous fiber laser according to claim 2, characterized in that: The optical fiber grating is manufactured by a hydrogen-carrying mask plate photolithography process, and the reflectivity of the optical fiber grating is 10% to 99.5%.

6. The continuous fiber laser according to any one of claims 1 to 5, characterized in that: The wavelength filtering range of the composite resonant cavity is 1030nm to 2020nm.

7. The continuous fiber laser according to claim 1, characterized in that An end cap is arranged on the output end of the output device, an anti-reflection film is arranged on the end cap, and a roughened area is arranged inside the output device.

8. The continuous fiber laser according to claim 1, characterized in that: An end of the second stripper facing away from the second combiner has a bevel angle, and the angle of the bevel angle is 6° to 10°.

9. The continuous fiber laser according to claim 1, characterized in that: The first beam combiner is a forward beam combiner, and the plurality of first pump sources are respectively connected to one end of the first beam combiner facing the first stripper through pump fibers; The second beam combiner is a reverse beam combiner, and a plurality of the second pump sources are respectively connected to one end of the second beam combiner facing the second stripper through pump fibers.

10. The continuous fiber laser according to claim 1, characterized in that: The signal-to-noise ratio of the composite resonant cavity is 0.06-0.1.

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