Continuous-wave fiber laser

Abstract

A continuous-wave fiber laser, relating to the technical field of lasers. The continuous-wave fiber laser comprises: an output device (10), a first stripper (20), a first beam combiner (30), a compound resonant cavity (70), a second beam combiner (40), and a second stripper (50) which are sequentially connected by means of a central fiber, wherein the compound resonant cavity (70) is internally provided with a plurality of sub-cavities, and the sub-cavities are used for filtering and enhancing a laser beam. The continuous-wave fiber laser further comprises: a plurality of first pumping sources (61) and a plurality of second pumping sources (62), wherein the plurality of first pumping sources (61) are separately connected to the first beam combiner (30), and the plurality of second pumping sources (62) are separately connected to the second beam combiner (40).

Description

Continuous fiber laser Technical Field

[0001] This invention relates to the field of laser technology, and in particular to a continuous fiber laser. Background Technology

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

[0003] The center wavelength and spectral linewidth of high-power, narrow-linewidth fiber lasers are primarily determined by the characteristics of the seed source. Due to the self-pulsation effect, when the power of a multi-mode oscillating seed source laser is amplified to several kilowatts, it manifests as broadening of the laser peak and enhancement of the Raman peak in the spectrum. The degradation of laser spectral purity leads to adverse effects on subsequent spectral beam combining applications, such as reduced efficiency, increased stray light, and deteriorated beam quality.

[0004] Optical fibers have high power density, making them highly susceptible to various nonlinear effects during laser amplification, such as stimulated Brillouin scattering (SBS), self-phase modulation (SPM), four-wave mixing (FWM), and stimulated Raman scattering (SRS). Current methods for suppressing these nonlinear effects suffer from either low efficiency or excessive cost. Summary of the Invention

[0005] The main objective of this invention is to propose a continuous fiber laser, which aims to solve the technical problems of low efficiency or high cost in existing methods for suppressing nonlinear effects.

[0006] To achieve the above objectives, the present invention proposes a continuous fiber laser, which includes an output device, a first stripper, a first combiner, a composite resonant cavity, a second combiner, and a second stripper connected sequentially via a central fiber. The composite resonant cavity has multiple sub-cavities, which are used to filter and enhance the laser beam.

[0007] The continuous fiber laser also includes:

[0008] Multiple first pump sources are connected to the first combiner, respectively.

[0009] Multiple second pump sources are connected to the second combiner.

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

[0011] Multiple fiber Bragg gratings are connected in sequence;

[0012] An active optical fiber is disposed between any two adjacent fiber gratings, wherein all the fiber gratings located on one side of the active optical fiber and any one fiber grating 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 multiple fiber Bragg gratings are arranged sequentially at intervals, wherein any two fiber Bragg gratings form a sub-cavity.

[0014] In one embodiment, the active optical fiber includes Yb 3+ Er 3+ Tm 3+ Ho 3+ Dy 3+ It consists of one or more dopants.

[0015] In one embodiment, the fiber grating is fabricated using a hydrogen-loaded mask photolithography process, and the reflectivity of the fiber 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, the output terminal of the output device is provided with an end cap, the end cap is provided with an anti-reflection membrane, and the interior of the output device has a texturing region.

[0018] In one embodiment, the end of the second stripper facing away from the second bundler has a chamfer angle, the chamfer angle being 6° to 10°.

[0019] In one embodiment, the first bundler is a forward bundler, and a plurality of the first pump sources are respectively connected to one end of the first bundler facing the first stripper via pump fibers;

[0020] The second bundler is a reverse bundler, and multiple second pump sources are respectively connected to one end of the second bundler facing the second stripper via pump fibers.

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

[0022] The technical solution of this invention incorporates the aforementioned composite resonant cavity into the optical path structure, employing a nonlinear suppression technique for continuous fiber lasers. The composite resonant cavity includes multiple sub-cavities. The oscillation longitudinal mode of a single sub-cavity is significantly affected by thermal effects, inducing continuous parasitic oscillations that exacerbate the self-pulse of the pump source. After forming the composite resonant cavity, the oscillation longitudinal mode must simultaneously satisfy the resonant structure of multiple sub-cavities, which is beneficial for stabilizing the oscillation frequency and filtering out unnecessary nonlinear spectral components. The overall structure is simple, consisting only of an output unit, a stripper, and a beam combiner, achieving low-cost and high-efficiency suppression of nonlinear effects. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

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

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

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

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

[0028] Figure 5a shows the self-pulse spectrum test results of the continuous fiber laser of the present invention without the use of a composite resonant cavity.

[0029] Figure 5b shows the self-pulse spectrum test results of the continuous fiber laser of the present invention using the composite resonant cavity method.

[0030] Figure 6 shows the characteristic spectral test diagram of the nonlinear effect of the continuous fiber laser of the present invention.

[0031] Explanation of icon numbers:

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

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

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort 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 positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indications will also change accordingly.

[0036] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0037] This invention proposes a continuous fiber laser.

[0038] Referring to Figure 1, in one embodiment of the present invention, the continuous fiber laser includes an output device 10, a first stripper 20, a first combiner 30, a composite resonant cavity 70, a second combiner 40, and a second stripper 50 connected sequentially via a central fiber. The composite resonant cavity 70 has multiple sub-cavities, which are used to filter and enhance the laser beam. The continuous fiber laser also includes multiple first pump sources 61 and multiple second pump sources 62. The multiple first pump sources 61 are respectively connected to the first combiner 30, and the multiple second pump sources 62 are respectively connected to the second combiner 40.

[0039] In an optical path, the light beam passes through various optical elements and exits from the laser. The direction in which the laser beam exits from the laser is generally defined as the positive direction of the optical path. In an optical path with the same optical structure, along the positive direction of each optical element, the side from which the beam exits is called the first end, and the side from which the beam enters is called the second end.

[0040] Please refer to Figure 1. From right to left, the components are: output device 10, first stripper 20, first bundler 30, composite resonant cavity 70, second bundler 40, and second stripper 50.

[0041] 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 are connected by a central fiber, and the optical path is positive from left to right.

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

[0043] Multiple first pump sources 61 are each connected to the first end of the first combiner 30 via an independent pump fiber. Multiple second pump sources 62 are each connected to the second end of the second combiner 40 via an independent pump fiber.

[0044] A pump source provides a laser beam, which is injected into the composite resonant cavity 70 through a pump fiber. The laser beam then continuously passes through the sub-cavities within the composite resonant cavity 70, where it is filtered and enhanced by the sub-cavities, ultimately forming a laser beam that is emitted from the output device 10.

[0045] Referring to Figure 1, the first bundler 30 is a forward bundler, and multiple first pump sources 61 are respectively connected to the end of the first bundler 30 facing the first stripper 20 via pump fibers; the second bundler 40 is a reverse bundler, and multiple second pump sources 62 are respectively connected to the end of the second bundler 40 facing the second stripper 50 via 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 methods can be used individually or in combination.

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

[0048] All bundlers can be of type (N+1)*1, such as (6+1)*1 bundlers, with 6 first pump sources 61. According to Figure 1, the left side of the first bundler 30 is the bundle-gathering end, which is connected to the composite resonant cavity 70, and the right side is the branch end, one of which is connected to the first stripper 20 through the central fiber, while the other branches are connected to one of the first pump sources 61.

[0049] Similarly, the second combiner 40 has a similar structure to the first combiner 30 but is oriented in the opposite direction. It uses a (6+1)*1 combiner, and the number of second pump sources 62 is also 6. Please refer to Figure 1, that is, the left side of the second combiner 40 is the branch end, and the right side is the combiner end.

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

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

[0052] The technical solution of this invention incorporates the composite resonant cavity 70 into the optical path structure, providing a nonlinear suppression technique for continuous fiber lasers. The composite resonant cavity 70 includes multiple sub-cavities. The oscillation longitudinal mode of a single sub-cavity is significantly affected by thermal effects, which can induce continuous parasitic oscillations and exacerbate the self-pulse of the pump source. After forming the composite resonant cavity 70, the oscillation longitudinal mode needs to simultaneously satisfy the resonance structure of multiple sub-cavities, which is beneficial for stabilizing the oscillation frequency and filtering out unnecessary nonlinear spectral components. The overall structure is simple, consisting only of an output unit 10, a stripper, and a combiner, achieving low-cost and high-efficiency suppression of nonlinear effects.

[0053] In one embodiment, the composite resonant cavity 70 includes multiple sub-cavities. The oscillation longitudinal mode of a single sub-cavity is significantly affected by thermal effects, which can induce continuous parasitic oscillations and exacerbate the self-pulse of the pump source. After forming the composite resonant cavity 70, the oscillation longitudinal mode needs to simultaneously satisfy the resonant structure of multiple sub-cavities, which is beneficial for stabilizing the oscillation frequency and filtering out unnecessary nonlinear spectral components. The overall structure is simple, consisting only of an output device 10, a stripper, and a beam combiner, achieving low-cost and high-efficiency suppression of nonlinear effects.

[0054] In this embodiment, the active optical fiber 72 can be a high-gain doped active optical fiber 72. It can be any type of high-gain rare-earth doped optical fiber, with components including Yb. 3+ Er 3+ Tm 3+ Ho 3+ or Dy 3+ Its composition can be achieved by using at least one component as a single doping agent, using two components as a double doping agent, or using a combination of more than two components.

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

[0056] In this embodiment, the fiber optic grating 71 can be obtained using a hydrogen-loaded mask photolithography process. The center wavelength of the fiber optic grating 71 in this embodiment can be set in the range of 1030nm to 2020nm, thereby enabling the composite resonant cavity 70 to have a wavelength filtering range of 1030nm to 2020nm. The reflectivity of the fiber optic grating 71 is in the range of 10% to 99.5%.

[0057] Multiple fiber Bragg gratings 71 are spaced apart, and the position of the active fiber 72 is adjusted to combine the multiple fiber Bragg gratings 71 and the active fiber 72 to form different subcavities.

[0058] Please refer to Figure 2. In this embodiment, multiple fiber Bragg gratings 71 are arranged from left to right as a1, a2, a3, a4, a5, a6, etc. The active fiber 72 is disposed on the left optical path of the a6th fiber Bragg grating 71 and connected to the a6th fiber Bragg grating 71.

[0059] In this structure, a1 and a6 form the first sub-cavity, which reflects the light beam emitted from the pump source. The light beam frequently passes through the active fiber 72 between a1 and a6, thereby enhancing the laser beam. Finally, the laser beam satisfies the center wavelength of the fiber grating 71 and is output to the output device 10 via the central fiber.

[0060] Similarly, a2 and a6 form the second sub-cavity, a3 and a6 form the third sub-cavity, and so on. The more fiber gratings 71 there are, the more sub-cavities are formed. A greater number of fiber gratings 71 improves the laser filtering accuracy, ensuring that only lasers with wavelengths within a set range are emitted. In this embodiment, the wavelength range is taken as 1030nm to 2020nm.

[0061] As another implementation, the position of the active optical fiber 72 can be adjusted. Referring to Figure 3, the active optical fiber 72 can be positioned between a1 and a2, forming a first sub-cavity between a1 and a2, a second sub-cavity between a1 and a3, a third sub-cavity between a1 and a4, and so on.

[0062] In another embodiment, there are multiple active optical fibers 72, and multiple active optical fibers 72 and multiple fiber gratings 71 are arranged sequentially at intervals, wherein any two fiber gratings 71 form a sub-cavity.

[0063] Referring to Figure 4, by increasing the number of active optical fibers 72, with one active optical fiber 72 placed between every two adjacent fiber Bragg gratings 71, a sub-cavity can be formed between any two fiber Bragg gratings 71 in this embodiment. This further increases the number of sub-cavities formed, improving efficiency.

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

[0065] In one embodiment, the output terminal of the output device 10 is provided with an end cap 11, the end cap 11 is provided with an anti-reflection film, and the interior of the output device 10 has a texturized region.

[0066] In this embodiment, the output device 10 uses 50 / 400 / 0.12 passive optical fiber. Referring to Figure 1, the output end of the output device 10 is on the right side, and is fused to a quartz end cap 11 coated with an antireflection film. The output device 10 contains texturing regions created by etching with abrasive paste or CO2 laser etching, which are used to achieve forward cladding stripping and reverse cladding stripping.

[0067] The light from 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 output wavelength of the pump source is 915nm, the output power of the pump source is ≥650W, 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 achieve the output of continuous 1080nm laser.

[0069] The center wavelength range of the fiber optic grating 71 is 1030–2020 nm, and its spectral bandwidth ranges from 1 nm to 4 nm. In this embodiment, a center wavelength of 1080 nm and a spectral bandwidth of 3 nm are selected as examples for illustration. The reflectivity of the fiber optic grating 71 is 10%–99.5%.

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

[0071] Furthermore, as an embodiment, a practical demonstration is performed using the above parameters. Figure 5a shows the self-pulse spectrum test results of the continuous fiber laser of the present invention without the composite resonant cavity 70, and Figure 5b shows the self-pulse spectrum test results of the continuous fiber laser of the present invention with the composite resonant cavity 70.

[0072] At a current of 10A, the signal-to-noise ratio (SNR) in Figure 5a is 0.18 when a conventional cavity structure is used instead of the composite resonant cavity 70; the SNR in Figure 5b is 0.06 when the composite resonant cavity 70 is used. This proves that the self-pulse effect of the seed source is suppressed in the composite resonant cavity 70 structure, thereby improving the nonlinear threshold.

[0073] Further, please refer to Figure 6, which shows the characteristic spectral test results of the nonlinear effect of the continuous fiber laser of the present invention. As can be seen from the figure, when a conventional cavity structure is used instead of the composite resonant cavity 70, the Raman peak and the main laser peak intensity differ by only 10 dB when the pump source power is 2636 W; while when the composite resonant cavity 70 is used and the pump source power is 3180 W, no Raman peak spectrum is observed, thus achieving the suppression of nonlinear effects.

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

[0075] The above description is merely an exemplary embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A continuous fiber laser, characterized in that, The continuous fiber laser includes an output device, a first stripper, a first combiner, a composite resonant cavity, a second combiner, and a second stripper connected in sequence via a central fiber. The composite resonant cavity has multiple sub-cavities, which are used to filter and enhance the laser beam. The continuous fiber laser also includes: Multiple first pump sources are connected to the first combiner, respectively. Multiple second pump sources are connected to the second combiner.

2. The continuous fiber laser as described in claim 1, characterized in that, The composite resonant cavity includes: Multiple fiber Bragg gratings are connected in sequence; An active optical fiber is disposed between any two adjacent fiber gratings, wherein all the fiber gratings located on one side of the active optical fiber and any one fiber grating on the other side of the active optical fiber form a sub-cavity.

3. The continuous fiber laser as described in claim 2, characterized in that, The number of active optical fibers is multiple, and the multiple active optical fibers and multiple fiber Bragg gratings are arranged sequentially at intervals, wherein any two fiber Bragg gratings form a sub-cavity.

4. The continuous fiber laser as described in claim 2, characterized in that, The active optical fiber includes Yb 3+ Er 3+ Tm 3 + Ho 3+ Dy 3+ It consists of one or more dopants.

5. The continuous fiber laser as described in claim 2, characterized in that, The fiber grating is fabricated using a hydrogen-loaded mask photolithography process, and its reflectivity ranges from 10% to 99.5%.

6. The continuous fiber laser as described in 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 as described in claim 1, characterized in that, The output terminal of the output device is provided with an end cap, the end cap is provided with an anti-reflection membrane, and the interior of the output device has a texturing region.

8. The continuous fiber laser as described in claim 1, characterized in that, The second stripper has a chamfered angle at the end opposite to the second bundler, the chamfered angle being 6° to 10°.

9. The continuous fiber laser as described in claim 1, characterized in that, The first bundler is a forward bundler, and multiple first pump sources are respectively connected to one end of the first bundler facing the first stripper via pump fibers; The second bundler is a reverse bundler, and multiple second pump sources are respectively connected to one end of the second bundler facing the second stripper via pump fibers.

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

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