2 [mu] m short-wavelength kilowatt-level fiber laser for suppressing parasitic oscillation

Abstract

The 2mum short-wavelength kilowatt-level fiber laser capable of suppressing parasitic oscillation can realize high-power laser output, reduce return light reflection of the end face of a fiber fusion point, and effectively suppress parasitic oscillation. The first pumping source enables the wavelength to be stably output for a long time at the strongest absorption peak of the gain medium by controlling the temperature, the optical fiber beam combiner couples the pumping light into the high-reflectivity optical fiber grating, the output is firstly welded with the single-mode doped gain optical fiber and then welded with the low-reflectivity optical fiber grating, and the residual pumping light is stripped through the cladding pumping light stripper; high-quality seed light is output; the optical fiber isolator prevents the amplifier from returning light to damage the pre-stage main oscillator, and the mode field adapter matches the mode fields of the oscillator and the amplifier; an optical fiber beam combiner couples a second pumping source and a preceding-stage signal into an optical fiber isolator doped gain optical fiber, a high-power cladding pumping light stripper is welded to strip residual pumping light, and 2-micron short-wave kilowatt-level laser is output; and the optical fiber welding positions behind the optical fiber isolator are all in oblique angle welding.

Description

Technical Field

[0001] The present invention relates to the technical field of lasers, and particularly to a 2-μm short-wavelength kilowatt-level fiber laser for suppressing parasitic oscillation. Background Art

[0002] The 2-μm high-power fiber laser has important applications in many fields such as laser medicine, lidar, and material processing. Especially in the field of biomedical treatment, since the output wavelength of the 2-μm fiber laser is located at the water molecule absorption peak, it causes little damage to soft tissues during the operation, has a good hemostatic effect, does not cause serious tissue necrosis and postoperative complications, and can effectively protect soft tissues while precisely excising diseased tissues. Compared with traditional 2-μm solid lasers and other light sources, the 2-μm fiber laser has the advantages of precise control, smooth wound surface, and thin coagulation layer, so it has broad application prospects and good clinical treatment effects in non-invasive surgeries (such as bladder urothelial carcinoma, kidney stones, and benign prostatic hyperplasia). In addition, the 2-μm fiber laser has the advantages of flexible transmission, small volume, good stability, and high conversion efficiency, which greatly improves the operation efficiency and convenience of laser surgery.

[0003] However, the reabsorption of the 2-μm laser with a short wavelength in the thulium-doped fiber is relatively strong. At high power operation, the reflection at the fiber end face or the fiber fusion joint position will form an unexpected resonance path, resulting in the phenomenon of parasitic oscillation, which severely limits the output power of the 2-μm laser with a short wavelength. The local energy accumulation generated by the parasitic laser transmitted in the reverse direction may trigger the fiber fuse phenomenon, thus causing permanent damage to the fiber and fiber devices. Summary of the Invention

[0004] To overcome the defects of the prior art, the technical problem to be solved by the present invention is to provide a 2-μm short-wavelength kilowatt-level fiber laser for suppressing parasitic oscillation, which can achieve high-power laser output, reduce the back reflection of light at the fiber fusion joint end face, and effectively suppress parasitic oscillation.

[0005] The technical solution of the present invention is: This 2-μm short-wavelength kilowatt-level fiber laser for suppressing parasitic oscillation includes: a single-mode fiber master oscillator, a fiber isolator (7), a mode field adapter (8), and a large mode field fiber amplifier;

[0006] The single-mode fiber master oscillator includes: a first pump source (1), an optical fiber coupler (2), a high-reflectivity fiber grating (3), a single-mode doped gain fiber (4), a low-reflectivity fiber grating (5), and a cladding pump light stripper (6); the internal laser diode of the first pump source is placed on a temperature controller, and the wavelength is stably output for a long time at the strongest absorption peak of the gain medium by controlling the temperature. The first pump source couples the pump light into the high-reflectivity fiber grating through the optical fiber coupler. The output of the high-reflectivity fiber grating is first fused to the single-mode doped gain fiber and then to the low-reflectivity fiber grating. The residual pump light is stripped by the cladding pump light stripper to output high-quality seed light;

[0007] The pigtail of the cladding pump light stripper is first fused to an optical fiber isolator to block the return light from the amplifier and damage the pre-stage master oscillator, and then fused to a mode field adapter to match the mode fields of the oscillator and the amplifier;

[0008] The large-mode-field fiber amplifier includes: a second pump source (9), an optical fiber coupler (10), an amplifier large-mode-field doped gain fiber (11), and a high-power cladding pump light stripper (12); the second pump source and the pre-stage signal are first coupled into the doped gain fiber of the optical fiber isolator through the optical fiber coupler, and the high-power cladding pump light stripper is fused to strip the residual pump light to output a 2-μm short-wavelength kilowatt-level laser; the fiber fusion positions after the optical fiber isolator are all angled fusions.

[0009] The beneficial technical effects of the present invention are as follows:

[0010] 1. By regulating the output end of the fiber amplifier and the fiber fusion angle, the present invention reduces the return light from the fiber end face, increases the threshold of the parasitic oscillation phenomenon, effectively suppresses the parasitic oscillation, and greatly improves the output power of the 2-μm short-wavelength laser.

[0011] 2. In the fiber amplifier of the present invention, the appropriate fiber length is calculated according to the absorption coefficient of the gain fiber, and the length of the gain fiber is precisely reduced by a large-mode-field fiber precision cutter. While suppressing the parasitic oscillation, the amplified spontaneous emission light (ASE) is reduced, and the output power and signal-to-noise ratio of the 2-μm short-wavelength laser are improved. In addition, in the present invention, all the optical fibers and optical fiber devices adopt the fiberized fusion method, making the laser structure compact and the performance stable. Description of the Drawings

[0012] Figure 1 It is a schematic structural diagram of a 2-μm short-wavelength kilowatt-level fiber laser for suppressing parasitic oscillation of the present invention.

[0013] Figure 2 It is a schematic diagram of the angled fusion method for suppressing parasitic oscillation of the present invention. Detailed Embodiment

[0014] To enable those skilled in the art to better understand the solution of the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0015] It should be noted that the term "including" in the specification and claims of the present invention and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, device, product or equipment that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or equipment.

[0016] As Figure 1 shown, this 2μm short-wavelength kilowatt-level fiber laser for suppressing parasitic oscillation includes: a single-mode fiber master oscillator, an optical fiber isolator 7, a mode field adapter 8, and a large mode field fiber amplifier;

[0017] The single-mode fiber master oscillator includes: a first pump source 1, an optical fiber combiner 2, a high-reflectivity fiber grating 3, a single-mode doped gain fiber 4, a low-reflectivity fiber grating 5, and a cladding pump light stripper 6; the internal laser diode of the first pump source is placed on a temperature controller, and the wavelength is stably output for a long time at the strongest absorption peak of the gain medium by controlling the temperature. The first pump source couples the pump light into the high-reflectivity fiber grating through the optical fiber combiner. The output of the high-reflectivity fiber grating is first fused to the single-mode doped gain fiber and then to the low-reflectivity fiber grating. The residual pump light is stripped by the cladding pump light stripper to output high-quality seed light; the pigtail of the cladding pump light stripper is first fused to the optical fiber isolator to block the return light from the amplifier and damage the pre-stage master oscillator, and then fused to the mode field adapter to match the mode fields of the oscillator and the amplifier;

[0018] The large mode field fiber amplifier includes: a second pump source 9, an optical fiber combiner 10, an amplifier large mode field doped gain fiber 11, and a high-power cladding pump light stripper 12; the second pump source and the pre-stage signal are first coupled into the doped gain fiber of the optical fiber isolator through the optical fiber combiner, and the residual pump light is stripped by fusing the high-power cladding pump light stripper to output a 2μm short-wave kilowatt-level laser; the fiber fusion positions after the optical fiber isolator are all angled fusions.

[0019] The beneficial technical effects of the present invention are as follows:

[0020] 1. The present invention reduces the backward light at the fiber end face by adjusting the output end of the fiber amplifier and the fiber splicing angle, raises the threshold of the parasitic oscillation phenomenon, effectively suppresses the parasitic oscillation, and greatly improves the output power of the short-wavelength 2-μm laser.

[0021] 2. In the fiber amplifier of the present invention, the appropriate fiber length is calculated according to the absorption coefficient of the gain fiber, and the gain fiber length is precisely reduced by a large-mode-field fiber precision cutter. While suppressing the parasitic oscillation, the amplified spontaneous emission light (ASE) is reduced, and the output power and signal-to-noise ratio of the short-wavelength 2-μm laser are improved. In addition, in the present invention, all the fibers and fiber devices adopt the fiberized splicing method, making the laser structure compact and the performance stable.

[0022] Preferably, the laser resonator of the single-mode fiber master oscillator is a linear resonator or a ring resonator. Narrow-bandwidth single-mode laser can be output through the linear resonator or the ring resonator to ensure the beam quality of the seed light source for subsequent laser amplification.

[0023] Preferably, the output wavelength of the first pump source and the second pump source is adjusted by controlling the temperature through the control panel or the computer terminal, so that the wavelength is stably output for a long time at the strongest absorption peak of the gain medium.

[0024] Preferably, the single-mode fiber master oscillator and the first pump source couple the pump light into the high-reflectivity fiber grating through a fiber coupler. The output of the high-reflectivity fiber grating is first spliced with the doped gain fiber and then spliced with the low-reflectivity fiber grating, and high-quality seed light is output through the cladding pump light stripper.

[0025] Preferably, the large-mode-field fiber amplifier is a single-stage amplifier or a multi-stage amplifier. The length of the doped gain fiber includes all lengths that can effectively generate gain. The hierarchical amplification of the amplifier is beneficial to reducing the thermal accumulation of the gain fiber of the amplifier. Adjusting the gain fiber length according to the amplification stage of the amplifier can avoid the generation of strong ASE due to too long fiber.

[0026] Preferably, the single-mode doped gain fiber is one of the single-mode gain fibers doped with thulium, holmium, or co-doped with thulium and holmium. The 2-μm laser is at the peak of the emission spectrum of the thulium-doped and holmium-doped gain fiber, which can improve the gain efficiency.

[0027] Preferably, the large-mode-field doped gain fiber of the amplifier is one of the large-mode-field gain fibers doped with thulium, holmium, or co-doped with thulium and holmium. The 2-μm laser is at the peak of the emission spectrum of the thulium-doped and holmium-doped gain fiber, which can improve the gain efficiency.

[0028] Preferably, the bevel splicing for suppressing parasitic oscillation is the splicing of the passive fiber and the doped gain fiber at the amplification stage position or other positions, or the splicing of the passive fiber and the passive fiber.

[0029] Preferably, for the bevel fusion splicing that suppresses parasitic oscillation, the end face tilt angle θ is between 2 and 15 degrees. The bevel fusion splicing can introduce the return light from the original flat-angle fusion splicing end face into the fiber cladding, effectively reducing the parasitic oscillation in the cavity.

[0030] The embodiments of the present invention will be described in more detail below.

[0031] The present invention is the first to create a 2μm short-wavelength kilowatt-level high-power fiber laser based on the effective suppression of parasitic oscillation, which can achieve a kilowatt-level high-power 2μm fiber laser output. See Figure 1 , which is a schematic structural diagram of an embodiment of the present invention, including a first pump source 1 with a built-in temperature controller, an optical fiber combiner 2, a high-reflectivity fiber grating 3, a single-mode doped gain fiber 4, a low-reflectivity fiber grating 5, a cladding pump light stripper 6, an optical fiber isolator 7, a mode field adapter 8, a second pump source 9 with a built-in temperature controller, an optical fiber combiner 10, a large mode field doped gain fiber 11, and a cladding pump light stripper 12. The first pump source 1 with a built-in temperature controller couples the pump light into the resonant cavity through the optical fiber combiner 2. The output of the optical fiber combiner 2 is first fused with the high-reflectivity fiber grating 3, and then the single-mode doped gain fiber 4, the low-reflectivity fiber grating 5, the cladding pump light stripper 6, the optical fiber isolator 7, and the mode field adapter 8 are fused in sequence along the head and tail of the laser. The second pump source 9 with a built-in temperature controller is coupled into the large mode field doped gain fiber 11 through the optical fiber combiner 10, followed by the cladding pump light stripper 12, and the other end is used as the output end to output the laser. The fusion splicing method of all optical fiber devices after the optical fiber isolator 7 adopts bevel fusion splicing.

[0032] Specifically, for the first and second pump sources with built-in temperature controllers, the pump wavelength can be controlled by adjusting the temperature through the control panel, so that the wavelength stably outputs for a long time at the strongest absorption peak of the gain medium, ensuring the pump efficiency.

[0033] The single-mode master oscillator resonant cavity couples the pump light into the resonant cavity and generates the required seed light through the oscillation of the high- and low-reflectivity fiber gratings.

[0034] The optical fiber isolator and the mode field adapter can isolate the resonant cavity from the optical fiber amplifier and perform mode field matching, ensuring that the backward light will not damage the previous stage and realizing the connection and matching of optical fibers with different specifications.

[0035] The large mode field optical fiber amplifier couples the pre-stage signal fiber and the pump source with a built-in temperature controller through a combiner, fuses the gain fiber to amplify the signal light, and then fuses the cladding pump light stripper to strip the remaining light in the cladding.

[0036] The method for suppressing parasitic oscillation reduces amplified spontaneous emission light (ASE) by controlling the length of the large-mode field gain fiber of the amplifier, and improves the output power and signal-to-noise ratio of the 2-μm short-wavelength laser. By controlling the fiber splicing angle of all devices after the fiber isolator, the oscillation of the end-face return light in the amplifier is reduced, the generation of parasitic oscillation is effectively suppressed, and the output of kilowatt-level high-power laser is achieved.

[0037] As can be seen from the above embodiments, the present invention innovatively adopts the method of splicing the gain fiber in and out at an oblique angle in the amplifier part of the fiber laser to reduce the backlight reflection of the splicing end face, suppress the oscillation of the return light in the gain fiber, and further suppress the occurrence of parasitic oscillation. It effectively solves the problem that the output power of the current 2-μm fiber laser is low due to the influence of parasitic oscillation, and also provides a simple, low-cost and highly effective way to solve parasitic oscillation at present.

[0038] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A 2-μm short-wavelength kilowatt-level fiber laser for suppressing parasitic oscillation, characterized in that: It includes: A single-mode fiber master oscillator, an optical fiber isolator (7), a mode field adapter (8), and a large mode field fiber amplifier; The single-mode fiber master oscillator includes: a first pump source (1), an optical fiber coupler (2), a high-reflectivity fiber grating (3), a single-mode doped gain fiber (4), a low-reflectivity fiber grating (5), and a cladding pump light stripper (6); The internal laser diode of the first pump source is placed on a temperature controller, and the wavelength is stably output for a long time at the strongest absorption peak of the gain medium by controlling the temperature. The first pump source couples the pump light into the high-reflectivity fiber grating through the optical fiber coupler. The output of the high-reflectivity fiber grating is first fused to the single-mode doped gain fiber and then to the low-reflectivity fiber grating. The residual pump light is stripped by the cladding pump light stripper to output high-quality seed light; The pigtail of the cladding pump light stripper is first fused to the optical fiber isolator to block the light returned from the amplifier from damaging the pre-stage master oscillator, and then fused to the mode field adapter to match the mode fields of the oscillator and the amplifier; The large mode field fiber amplifier includes: a second pump source (9), an optical fiber coupler (10), an amplifier large mode field doped gain fiber (11), and a high-power cladding pump light stripper (12); The second pump source and the pre-stage signal are first coupled into the doped gain fiber of the optical fiber isolator through the optical fiber coupler, and the high-power cladding pump light stripper is fused to strip the residual pump light to output a 2-μm short-wave kilowatt-level laser; The fiber fusion positions after the optical fiber isolator are all angled fusions.

2. The 2-μm short-wavelength kilowatt-level fiber laser for suppressing parasitic oscillation according to claim 1, wherein: The laser resonator of the single-mode fiber master oscillator is a linear resonator or a ring resonator.

3. The 2μm short-wavelength kilowatt-level fiber laser for suppressing parasitic oscillation according to claim 2, wherein: The first pump source and the second pump source adjust the output wavelength by controlling the temperature through the control panel or the computer terminal, so that the wavelength is stably output for a long time at the strongest absorption peak of the gain medium.

4. The 2-μm short-wavelength kilowatt-level fiber laser for suppressing parasitic oscillation according to claim 3, wherein: The single-mode fiber master oscillator and the first pump source couple the pump light into the high-reflectivity fiber grating through the optical fiber coupler. The output of the high-reflectivity fiber grating is first fused to the doped gain fiber and then to the low-reflectivity fiber grating, and high-quality seed light is output through the cladding pump light stripper.

5. The 2-μm short-wavelength kilowatt-level fiber laser for suppressing parasitic oscillation according to claim 4, wherein: The large mode field fiber amplifier is a single-stage amplifier or a multi-stage amplifier, and the length of the doped gain fiber includes all lengths that can effectively generate gain.

6. The 2-μm short-wavelength kilowatt-level fiber laser for suppressing parasitic oscillation according to claim 5, characterized in that: The single-mode doped gain fiber is one of the single-mode gain fibers doped with thulium, holmium, or co-doped with thulium and holmium.

7. The 2-μm short-wavelength kilowatt-level fiber laser for suppressing parasitic oscillation according to claim 6, wherein: The amplifier large mode field doped gain fiber is one of the large mode field gain fibers doped with thulium, holmium, or co-doped with thulium and holmium.

8. The 2μm short-wavelength kilowatt-level fiber laser for suppressing parasitic oscillation according to claim 7, wherein: The angled fusion for suppressing parasitic oscillation is the fusion of a passive optical fiber and a doped gain fiber, or the fusion of a passive optical fiber and a passive optical fiber at the amplification stage position or other positions.

9. The 2-μm short-wavelength kilowatt-level fiber laser for suppressing parasitic oscillation according to claim 8, characterized in that: For the angled fusion for suppressing parasitic oscillation, the end face tilt angle θ is between 2 and 15 degrees.

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