CN215497520U

CN215497520U - Optical fiber laser

Info

Publication number: CN215497520U
Application number: CN202121262389.9U
Authority: CN
Inventors: 胡浩伟; 张思; 施建宏
Original assignee: Wuhan Raycus Fiber Laser Technologies Co Ltd
Current assignee: Wuhan Raycus Fiber Laser Technologies Co Ltd
Priority date: 2021-06-07
Filing date: 2021-06-07
Publication date: 2022-01-11
Anticipated expiration: 2031-06-07

Abstract

The present application relates to a fiber laser comprising: the pump light generating device comprises a pump light coupler and at least one pump source connected with the pump light coupler; the resonator comprises a resonant cavity structure welded with the pump optical coupler, and a gain optical fiber and a mode field adapter welded with the resonant cavity structure, wherein the gain optical fiber and the mode field adapter are welded; and an output optical cable fused with the resonator. Set up the mode field adapter in the syntonizer in this application, can be effectual with the high order mode at the stage filtering of just starting to vibrate, only guarantee that the basic mode can obtain effectual enlargeing, the energy of pump light only is used for the enlargeing to basic mode laser, can only obtain under the circumstances of basic mode laser like this, the effectual utilization ratio that improves the pump energy, the laser of being convenient for obtain the high power simultaneously.

Description

Optical fiber laser

Technical Field

The application relates to the technical field of lasers, in particular to a fiber laser.

Background

The fiber laser has the advantages of small volume, compact structure, simple heat management, maintenance-free full-fiber structure, good output beam quality, high power and the like, so that the fiber laser is widely applied to the fields of industrial processing, national defense, scientific research and the like. As a processing tool, in the field of industrial processing, a fiber laser is gradually replacing the market share of the conventional laser such as carbon dioxide laser, solid state laser, etc. by virtue of the above advantages.

In the industrial processing field, different laser energy distributions are applied differently, and single-mode laser energy distribution is Gaussian, has high energy density, and is mainly used in the fields of rapid cutting, precision machining, high-reflectivity material welding, 3D printing and the like of thin plates.

At present, a conventional single-mode continuous fiber laser adopts a single-cavity or MOPA (Master Oscillator Power-Amplifier) structure, and the used fiber is a single-mode double-clad fiber, so that the nonlinear effect Stimulated Raman (SRS) threshold is low due to the small fiber core diameter and the small cladding diameter of the single-mode double-clad fiber, and the improvement of output Power is limited. Therefore, how to obtain a high-power single-mode continuous fiber laser is an urgent problem to be solved at present.

Disclosure of Invention

The embodiment of the application provides a fiber laser, which aims to solve the problems that in the related art, due to the fact that the diameter of a fiber core of a single-mode double-clad fiber is small and the diameter of a cladding is small, the threshold value of a non-linear effect Stimulated Raman (SRS) is low, and the improvement of output power is limited.

In a first aspect, there is provided a fibre laser comprising:

the pump light generating device comprises a pump light coupler and at least one pump source connected with the pump light coupler;

the resonator comprises a resonant cavity structure welded with the pump optical coupler, and a gain optical fiber and a mode field adapter welded with the resonant cavity structure, wherein the gain optical fiber and the mode field adapter are welded; and the number of the first and second groups,

and the output optical cable is welded with the resonator.

In some embodiments, the resonant cavity structure includes a low-reflectivity grating and a high-reflectivity grating fused to the pump optical coupler, the high-reflectivity grating fused to the gain fiber, and the low-reflectivity grating fused between the mode field adapter and the output cable.

In some embodiments, the high-reflectivity grating and the low-reflectivity grating form a resonant cavity, and the gain fiber and the mode field adapter are disposed in the resonant cavity.

In some embodiments, the high reflective grating is configured as a few-mode fiber optic fiber and the low reflective grating is configured as a single-mode fiber.

In some embodiments, the high-reflectivity grating has a reflectivity of 99% or greater, and the low-reflectivity grating has a reflectivity of 10% ± 5%.

In some embodiments, the mode field adapter is integrally formed with the gain fiber.

In some embodiments, the first side of the pump optical coupler comprises 1 fiber and the second side of the pump optical coupler comprises N fibers;

the 1 path of optical fiber on the first side of the pump optical coupler is welded with the high-reflectivity grating;

m paths of optical fibers in the N paths of optical fibers on the second side of the pump optical coupler are respectively in one-to-one correspondence fusion with the output ends of the M pump sources;

wherein N is M +1, and M is a positive integer.

In some embodiments, the pump source is provided as a semiconductor fiber output laser.

In some embodiments, the optical fiber of the cladding light stripper is a single-mode optical fiber.

In some embodiments, the output fiber optic cable includes an output single mode fiber fused to the cladding light stripper, and an end cap fused to the output single mode fiber.

The beneficial effect that technical scheme that this application provided brought includes: set up the mode field adapter in the syntonizer in this application, can be effectual with the high order mode at the stage filtering of just starting to vibrate, only guarantee that the basic mode can obtain effectual enlargeing, the energy of pump light only is used for the enlargeing to basic mode laser, can only obtain under the circumstances of basic mode laser like this, the effectual utilization ratio that improves the pump energy, the laser of being convenient for obtain the high power simultaneously.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

Fig. 1 is a schematic structural diagram of a fiber laser provided in an embodiment of the present application;

fig. 2 is a schematic structural diagram of a mode field adapter according to an embodiment of the present application;

FIG. 3 is a schematic diagram of cladding shapes for three optical fibers provided in accordance with an embodiment of the present application;

FIG. 4 is a schematic diagram of a fundamental mode pattern in a mode field adapter provided in an embodiment of the present application;

fig. 5 is a schematic structural diagram of a fiber laser according to another embodiment of the present application.

In the figure: 1. a pump light generating device; 101. a pump source; 102. a pump optical coupler; 2. a resonator; 21. a resonant cavity structure; 103. high-reflection grating; 104. a gain fiber; 105. a mode field adapter; 106. a low-reflection grating; 107. an output optical cable; 108. a cladding light stripper.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

The embodiment of the application provides a fiber laser, which can solve the problems that the core diameter of a single-mode double-clad fiber is small, the cladding diameter is small, the threshold value of a nonlinear effect Stimulated Raman (SRS) is low, and the improvement of output power is limited.

As shown in fig. 1, a fiber laser includes: the optical fiber pump comprises a pump light generating device 1, a resonator 2 and an output optical cable 107, wherein the resonator 2 is arranged between the pump light generating device 1 and the output optical cable 107. The pump light generation device 1 comprises a pump light coupler 102 and at least one pump source 101 connected with the pump light coupler 102, wherein the pump source 101 is used for generating pump light, the pump light coupler 102 is connected with the resonator 2, the pump light coupler 102 couples the pump light into the resonator 2, and the pump light pumps lower-level particles in a gain medium of the resonator 2 to an upper level to form population inversion, so that laser light is obtained. The output optical cable 107 is fusion-spliced to the resonator 2 for outputting laser light.

The resonator 2 comprises a resonant cavity structure 21, a gain fiber 104 and a mode field adapter 105, wherein the resonant cavity structure 21 is welded with the pump optical coupler 102, the gain fiber 104 and the mode field adapter 105 are arranged in the resonant cavity structure 21, the gain fiber 104 and the mode field adapter 105 are both welded with the resonant cavity structure 21, and meanwhile the gain fiber 104 and the mode field adapter 105 are welded with each other. The gain fiber 104 is mainly a glass-doped rare-earth ytterbium fiber for radiating near-infrared laser light of a band near 1 um.

The laser oscillates and amplifies between the resonator structures 21 and filters out the resonator structures 21 when a predetermined power is reached. The gain fiber 104 serves as a gain medium, and the particles at the lower energy level in the gain medium are pumped to the upper energy level by the pump light to form the population inversion.

The mode field adapter 105 mainly functions to make the diameter of the fundamental mode field of the few-mode fiber consistent with that of the single-mode fiber in a fused tapering manner, so that the fundamental mode is smoothly transited from the few-mode fiber to the single-mode fiber, and a high-order mode is lost into a cladding.

Wherein the number of modes that the fiber can accommodate can be characterized by a normalized frequency V,

d is the diameter of the fiber core, NA is the numerical aperture of the fiber core, and lambda is the laser wavelength, so that the number of modes which can be contained in the fiber core is represented, when V is less than 2.405, the fiber is a single-mode fiber and can only transmit one mode, and the laser energy output by the fiber is in Gaussian distribution and is single-mode laser. When V > 2.405, the fiber is a multimode fiber, and is a few-mode or multimode fiber according to the mode number N.

Set up mode field adapter 105 in syntonizer 2 in this application, can be effectual with the high order mode at the stage filtering of just starting to vibrate, only guarantee that the fundamental mode can obtain effectual enlargeing, the energy of pump light is only used for the enlargeing to fundamental mode laser, can only obtain under the circumstances of fundamental mode laser guaranteeing like this, the effectual utilization ratio that improves the pumping energy has the laser of being convenient for to obtain the high power simultaneously.

Optionally, in another embodiment of the present application, the resonant cavity structure 21 includes a high-reflectivity grating 103 and a low-reflectivity grating 106, the high-reflectivity grating 103 is fused between the gain fiber 104 and the pump optical coupler 102, and the low-reflectivity grating 106 is fused between the mode field adapter 105 and the output cable 107, that is, the pump optical coupler 102, the high-reflectivity grating 103, the gain fiber 104, the mode field adapter 105, and the low-reflectivity grating 106 are sequentially fused.

Wherein, the high-reflection grating 103 is a high-reflection Bragg chirped fiber grating, the reflectivity is more than or equal to 99%, the central wavelength of the grating is 1060-1090nm, the reflection 3dB bandwidth is 2-3nm, the fiber is a large-mode-area double-cladding few-mode or multi-mode fiber, the diameter of a fiber core is 20-25um, the numerical aperture of the fiber core is 0.04-0.07, the diameter of a cladding is 350-450um, and the numerical aperture of the cladding is 0.4-0.5. The large mode field area of the fiber core can effectively improve the SRS threshold value, and the large cladding diameter and the numerical aperture can effectively improve the pumping power injected into the inner cladding of the double-cladding fiber, wherein the double-cladding fiber can pump in the cladding so as to improve the output power.

The low reflective grating 106 is a low reflective Bragg chirped fiber grating with reflectivity of 10% +/-5%, grating center wavelength of 1060-1090nm, reflective 3dB bandwidth of 1-1.5nm, the fiber is a large mode field area double-cladding single-mode fiber, the diameter of a fiber core is 10-14um, the numerical aperture of the fiber core is 0.06-0.07, the diameter of a cladding is 200-300um, and the numerical aperture of the cladding is 0.4-0.5.

As shown in fig. 2, the mode field adapter 105 reduces the core diameter of the few-mode fiber 201 (high reflective grating 103) by fusion tapering, so that the mode field diameter of the tapered fiber fundamental mode matches the mode field diameter of the single-mode fiber 203 (low reflective grating 106), and the fundamental mode loss is minimized. To simplify the process, mode field adapter 105 may be integrally formed with gain fiber 104. Higher order modes are lost to the cladding through the tapered region 202 because they cannot propagate in a single mode fiber.

As shown in fig. 3, among the few-mode fibers 201 (refer to fig. 2) there are various types, which may be a gain fiber 301 whose cladding shape is octagonal; the passive few-mode fiber 302 may also be a round cladding, the gain fiber 301 and the passive few-mode fiber 302 may also be fused with the single-mode fiber 303 in a low-loss manner by fusion tapering, and the cladding of the single-mode fiber 303 may be a round cladding.

As shown in fig. 4, several different modes may exist in the few-mode fiber, such as a fundamental mode LP01 mode 401, a high-order mode LP11 mode 402, a fundamental mode LP02 mode 403, etc., the high-order mode LP11 mode 402, the fundamental mode LP02 mode 403, etc. cannot pass through the taper without loss because the mode field diameter is larger than the fundamental mode field diameter, and thus leaks into the cladding from the taper, in the figure, the high-order mode 405 is the high-order mode leaking into the cladding from the taper, and the fundamental mode 403 is the fundamental mode in the thin fiber after being transmitted through the mode field adapter 105, and finally only the fundamental mode 403 adapted to the mode field can be transmitted in the fundamental mode fiber.

Wherein, the fundamental mode field diameter MFD in the optical fiber can be approximated by a formula,

wherein V is the normalized frequency of the optical fiber, and r is the radius of the fiber core of the optical fiber. Due to the difference of the optical fiber parameters, the corresponding difference of the fundamental mode field diameter can be generated, thereby generating the mode field mismatch loss. The mode field mismatch loss can be represented by the following equation:

it is shown where MFD1 is the fundamental mode field diameter of the first fiber and MFD2 is the fundamental mode field diameter of the second fiber.

In the resonator 2, both few-mode fibers and single-mode fibers exist, a high-order mode other than the fundamental mode also exists in the resonant cavity structure 21 during laser oscillation starting, the high-order mode can be effectively filtered out at the stage of the initial oscillation through the mode field adapter 105, only the fundamental mode can be effectively amplified, and pumping energy is only used for amplifying the fundamental mode laser, so that only the fundamental mode laser can be obtained, and meanwhile, the utilization rate of the pumping energy is effectively improved. In addition, the mode field area of the small-mode optical fiber with the large mode field area is larger than that of the single-mode optical fiber, and the SRS nonlinear effect can be inhibited under the condition of obtaining higher laser power.

Alternatively, in another embodiment of the present application, the high reflective grating 103 and the low reflective grating 106 provide two mirrors of the resonator structure 21, and the gain fiber 104 and the mode field adapter 105 are disposed in the resonator structure 21.

Optionally, in another embodiment of the present application, the first side of the pump optical coupler 102 includes 1 optical fiber, the second side of the pump optical coupler 102 includes N optical fibers, the 1 optical fiber of the first side of the pump optical coupler 102 is welded to the high reflective grating 103, and M optical fibers of the N optical fibers of the second side of the pump optical coupler 102 are welded to output ends of M pump sources 101 in a one-to-one correspondence manner, where N is M +1, and M is a positive integer. The pump optical coupler 102 is used to couple pump light generated by the plurality of pump sources 101 into the inner cladding of the double-clad fiber (gain fiber 104), and may be (6+1) × 1 or (18+1) × 1, or the like.

Optionally, in another embodiment of the present application, the pump source 101 is a semiconductor fiber output laser with a wavelength range of 900-.

Optionally, as shown in fig. 5, in another embodiment of the present application, the fiber laser further includes a cladding light stripper 108 disposed between the low reflective grating 106 and the output optical cable 107, and the optical fibers used for the output grating (low reflective grating 106), the cladding light stripper 108, and the output optical cable 107 are all single-mode optical fibers, and are used for maintaining the core laser as pure single-mode laser. The cladding light stripper 108 is used for stripping the high-order mode laser lost to the cladding in the resonant cavity structure 21 and the residual pump light in the cladding so as to avoid influencing the quality of the output laser beam, the optical fiber of the cladding light stripper 108 is a large mode field area double-cladding single-mode optical fiber, the diameter of the fiber core is 10-14um, the numerical aperture of the fiber core is 0.06-0.07, the diameter of the cladding is 200-300um, and the numerical aperture of the cladding is 0.4-0.5.

Optionally, in further embodiments of the present application, the output optical cable 107 comprises an output single mode fiber fused to the cladding light stripper 108, and an end cap fused to the output single mode fiber. The output single-mode fiber and the end cap are packaged into a laser output head for reducing the energy density of the end face of the output fiber, the output optical cable 107 adopts a large-mode-field-area double-cladding single-mode fiber, the diameter of a fiber core is 10-14 mu m, the numerical aperture of the fiber core is 0.06-0.07, the diameter of a cladding is 200-300 mu m, and the numerical aperture of the cladding is 0.4-0.5.

In the description of the present application, it should be noted that the terms "upper", "lower", and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, which are only for convenience in describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and operate, and thus, should not be construed as limiting the present application. Unless expressly stated or limited otherwise, the terms "mounted," "connected," and "connected" are intended to be inclusive and mean, for example, that they may be fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art as appropriate.

It is noted that, in the present application, relational terms such as "first" and "second", and the like, are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

The above description is merely exemplary of the present application and is presented to enable those skilled in the art to understand and practice the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A fiber laser, characterized in that it comprises:

and the output optical cable is welded with the resonator.

2. The fiber laser of claim 1, wherein the resonant cavity structure includes a low-reflection grating and a high-reflection grating fused to the pump optical coupler, the high-reflection grating being fused to the gain fiber, the low-reflection grating being fused between the mode field adapter and the output cable.

3. The fiber laser of claim 2, wherein the high-reflectivity grating and the low-reflectivity grating form a resonant cavity, the gain fiber and the mode field adapter being disposed within the resonant cavity.

4. The fiber laser of claim 2, wherein the high reflectivity grating is configured as a few-mode fiber and the low reflectivity grating is configured as a single-mode fiber.

5. The fiber laser of claim 2, wherein the high-reflectivity grating has a reflectivity of 99% or greater and the low-reflectivity grating has a reflectivity of 10% ± 5%.

6. The fiber laser of claim 2, wherein the mode field adapter is integrally formed with the gain fiber.

7. The fiber laser of claim 2, wherein the first side of the pump optical coupler comprises 1 fiber and the second side of the pump optical coupler comprises N fibers;

wherein N is M +1, and M is a positive integer.

8. The fiber laser of claim 1, wherein the pump source is provided as a semiconductor fiber output laser.

9. The fiber laser of claim 2, further comprising a cladding stripper disposed between the low-reflection grating and the output cable, the fiber of the cladding stripper being a single mode fiber.

10. The fiber laser of claim 9, wherein the output cable includes an output single mode fiber fused to the cladding stripper, and an end cap fused to the output single mode fiber.