Multiband high power multicore fiber laser

Abstract

The application relates to a multi-band high-power multi-core optical fiber laser, which comprises a pump excitation module, a pump beam combination module, a multi-band laser light source module and a light beam output module connected in sequence, the pump beam combination module is used for combining multiple multimode pump lasers generated by the pump excitation module into a high-power pump laser, the multi-band laser light source module is used for generating multiple target laser beams corresponding to target wave bands, and the light beam output module is used for separating the multiple target laser beams and respectively outputting the target laser beams corresponding to the target wave bands, wherein the multi-band laser light source module comprises a first multi-core fiber grating, a multi-core double-clad active optical fiber and a second multi-core fiber grating connected in sequence, the first multi-core fiber grating is connected with the pump beam combination module, and the second multi-core fiber grating is connected with the light beam output module; the application can solve the problems of a small number of working wave bands, a small wavelength interval and a low output power of the optical fiber laser.

Description

Technical Field

[0001] The present application relates to the field of laser technology, and in particular to a multi-band high-power multi-core fiber laser. Background Art

[0002] At present, fiber lasers capable of multi-band output often use single-core rare earth ion-doped fiber as the laser working medium, and combine multiple frequency-selective devices to construct a laser resonant cavity to achieve simultaneous lasing and output of lasers in different bands or different wavelengths in the same band.

[0003] However, existing multi-band (wavelength) fiber lasers are limited by the single-core working medium material and free-space optical path structure, as well as the mode competition effect between the wavelengths in the laser resonant cavity. They have problems such as a small number of working bands, small wavelength intervals and low output power. Summary of the Invention

[0004] Based on this, it is necessary to provide a multi-band high-power multi-core fiber laser that can increase the number of working bands and increase the wavelength interval to address the above technical problems.

[0005] In a first aspect, the present application provides a multi-band high-power multi-core fiber laser, comprising:

[0006] A pump excitation module for generating multiple multi-mode pump lasers;

[0007] The pump beam combining module is connected to the pump excitation module and is used to combine multiple multi-mode pump light sources into a high-power pump laser beam;

[0008] A multi-band laser light source module is connected to the pump beam combining module. The multi-band laser light source module is used to generate target laser beams corresponding to multiple target bands;

[0009] The beam output module is connected to the multi-band laser light source module. The beam output module is used to split the multiple target laser beams and output the target laser beams corresponding to each target band respectively;

[0010] Among them, the multi-band laser light source module includes a first multi-core fiber Bragg grating, a multi-core double-clad active fiber and a second multi-core fiber Bragg grating connected in sequence, the first multi-core fiber Bragg grating is connected to a pump beam combining module, and the second multi-core fiber Bragg grating is connected to a beam output module. The number of cores of the multi-core double-clad active fiber is equal to the number of target laser beams. The core of the multi-core double-clad active fiber is doped with rare earth ions, and the rare earth ions are a combination of one or more lanthanide ions. The target band is located within the luminescence band of the rare earth ions.

[0011] In one embodiment, a fiber Bragg grating corresponding to a target wavelength band is inscribed on the bare core of the first multi-core fiber Bragg grating;

[0012] The bare core of the second multi-core fiber Bragg grating is inscribed with a fiber Bragg grating corresponding to the target wavelength band.

[0013] In one embodiment, the reflectivity and 3dB bandwidth of the second multi-core fiber Bragg grating for the target laser beam are smaller than those of the first multi-core fiber Bragg grating for the target laser beam.

[0014] In one embodiment, the lanthanide ions include Nd 3+ 、Yb 3+ 、Er 3+ 、Tm 3+ and Ho 3+ ; The doping concentration of rare earth ions is greater than 1wt%.

[0015] In one embodiment, the shape of each core in the multi-core double-clad active optical fiber is a circle with equal or unequal diameters, the circle includes a first circle and a second circle, the distance between the center of the first circle and the center of the second circle is a first value, the sum of the radius of the first circle and the radius of the second circle is a second value, and the first value is greater than or equal to a preset multiple of the second value;

[0016] The inner cladding shapes of multi-core double-clad active optical fibers include rectangle, hexagon, octagon or dodecagon.

[0017] In one embodiment, the pump excitation module includes multiple pump light sources, the output end of each pump light source is connected to the pump beam combining module, and the operating band of the multi-mode pump laser is associated with the type of rare earth ions.

[0018] In one embodiment, the pump combining module includes a pump combiner, the input end of the pump combiner is connected to the output end of the pump excitation module, and the output end of the pump combiner is connected to the first multi-core fiber Bragg grating;

[0019] The input end of the pump combiner is a plurality of multimode optical fibers whose core diameters are within a first numerical range, and the output end of the pump combiner is a multimode optical fiber whose core diameter is within a second numerical range, or a passive double-clad optical fiber whose inner cladding diameter is within the second numerical range, and the second numerical range is greater than or equal to the first numerical range.

[0020] In one embodiment, the light beam output module includes a cladding light filter and a wavelength splitter connected in sequence, and the cladding light filter is further connected to a second multi-core fiber Bragg grating.

[0021] In one embodiment, the cladding light filter is a passive double-clad optical fiber, and a preset area within the cladding light filter is coated with multiple layers of UV glue arranged from low to high refractive index along the direction from the input end to the output end of the cladding light filter, and the refractive index of each UV glue is greater than the refractive index of the inner cladding of the optical fiber of the cladding light filter.

[0022] In one embodiment, the input end of the wavelength splitter is a passive double-clad optical fiber, and the output end of the wavelength splitter is a plurality of passive single-clad optical fibers.

[0023] The multi-band high-power multi-core fiber laser comprises a pump excitation module, a pump beam combining module, a multi-band laser light source module and a beam output module connected in sequence. The pump beam combining module is used to combine multiple multi-mode pump lasers generated by the pump excitation module into a high-power pump laser. The pump excitation module is used to excite the multi-band laser light source module to generate target laser beams corresponding to multiple target bands. The beam output module is used to split the multiple target laser beams and output the target laser beams corresponding to each target band respectively. The multi-band laser light source module comprises a first multi-core fiber Bragg grating, a multi-core double-clad active fiber and a second multi-core double-clad active fiber connected in sequence. The multi-core fiber Bragg grating (FBG) is connected to the pump beam combining module, and the second multi-core fiber Bragg grating is connected to the beam output module. Since the number of cores of the multi-core double-clad active fiber is equal to the number of target laser beams, and the cores of the multi-core double-clad active fiber are doped with rare earth ions as laser working media, different fiber cores can be doped with different rare earth ions to simultaneously achieve efficient lasing and generation of target laser beams corresponding to multiple target bands. Compared with the existing multi-band (wavelength) fiber laser, the mode competition effect is avoided, and the problems of the existing fiber laser with a small number of working bands, small wavelength interval and low output power are solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the conventional technology, the following briefly introduces the drawings required for use in the embodiments or the conventional technology descriptions. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 1 is a structural block diagram of a multi-band high-power multi-core fiber laser in one embodiment;

[0026] Figure 2 Schematic diagram of the shapes of multiple cores of a multi-core double-clad active optical fiber in one embodiment;

[0027] Figure 3 Schematic diagram of the structure of a multi-band high-power multi-core fiber laser in one embodiment;

[0028] Figure 4 1. Output spectrum diagram of a multi-band high-power multi-core fiber laser in one embodiment;

[0029] Figure 5 FIG. 4 is an output spectrum diagram of a multi-band high-power multi-core fiber laser in another embodiment. DETAILED DESCRIPTION

[0030] To facilitate understanding of the present application, the present application will be described more fully below with reference to the accompanying drawings. The accompanying drawings provide embodiments of the present application. However, the present application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to make the disclosure of the present application more thorough and comprehensive.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. It will be understood that the terms "first," "second," etc., used herein may be used herein to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish a first element from another element.

[0032] As used herein, the singular forms "a," "an," and "the" may also include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "include," "comprising," "having," and the like specify the presence of stated features, integers, steps, operations, components, parts, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, components, parts, or combinations thereof. Furthermore, the term "and / or" as used in this specification includes any and all combinations of the relevant listed items.

[0033] Multi-band high-power fiber lasers have the characteristics of simultaneous multi-band operation, high output power, good beam quality, high conversion efficiency, and compact structure. They have broad application prospects in industrial processing, optical communications, multi-wavelength lidar, multi-parameter fiber optic sensing and other fields.

[0034] At present, fiber lasers capable of multi-band (wavelength) output often use single-core rare earth ion-doped fiber as the laser working medium, and combine multiple frequency-selective devices to construct a laser resonant cavity to achieve simultaneous lasing and output of different bands or different wavelengths in the same band (with small wavelength intervals). For example, using a single-core Er 3+Doped ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) double-clad fiber and two sets of front and back cavity mirrors (dichroic mirrors) to construct a composite FP resonant cavity, achieving dual-band laser output at wavelengths of 2.79μm and 1.59μm, with powers of 8.19W and 2.8W respectively, and a conversion efficiency of about 10%. However, due to the limitations of single-core working medium materials and free-space optical path structures, the fiber laser has a small number of working bands (typical value: dual bands), low conversion efficiency, and poor reliability. For another example, using a single-core Er 3+ and Yb 3+ A short linear resonant cavity was constructed using co-doped single-clad optical fiber and dual-channel narrowband polarization-maintaining fiber Bragg gratings, achieving simultaneous laser output at four wavelengths: 1548.91nm, 1549.31nm, 1549.73nm, and 1550.13nm, with a power of approximately 4.5mW. However, due to direct lasing using the same or similar gain range (within the same wavelength band) of the laser working medium, mode competition exists between the various wavelengths in the cavity, resulting in a small wavelength spacing, low output power, and poor reliability of the fiber laser.

[0035] In addition, multiple independently operating single-wavelength (for example, 1.0μm, 1.5μm, and 2.0μm) fiber lasers can be used to flexibly obtain multi-band laser output through wavelength division multiplexing or coherent beam combining. However, there are problems with the fiber laser's complex structure, high cost, and large size.

[0036] The multi-band high-power multi-core fiber laser provided in the embodiment of the present application is achieved by setting the number of cores of the multi-core double-clad active fiber to be equal to the number of the target laser beam, and doping different rare earth ions in each core of the multi-core double-clad active fiber as a laser working medium; the multi-core double-clad active fiber, the first multi-core fiber Bragg grating (rear cavity mirror) and the second multi-core fiber Bragg grating (front cavity mirror) together form a multi-band laser resonant cavity, and after the high-power multi-mode pump laser enters the multi-band laser resonant cavity, the different rare earth luminescent ions doped in the multiple cores in the multi-core double-clad active fiber generate The particle number is inverted, generating stimulated emission signal light of different bands. Under the continuous feedback of the front and rear cavity mirrors in different bands, the signal light in each core of the multi-core double-clad active optical fiber oscillates back and forth many times in its respective waveguide structure and is amplified many times, so that the pump excitation module can simultaneously and efficiently laser and generate multiple-band lasers (target laser beams corresponding to multiple target bands). The beam output module is then used to split the multiple target laser beams, so that the multiple-band lasers of the multi-core fiber laser (target laser beams corresponding to multiple target bands) can be separated and stably output.

[0037] In an exemplary embodiment, Figure 1As shown, a multi-band high-power multi-core fiber laser 100 is provided, comprising:

[0038] A pump excitation module 110 is used to generate multiple multi-mode pump lasers;

[0039] The pump beam combining module 120 is connected to the pump excitation module 110 and is used to combine multiple multi-mode pump light sources into a high-power pump laser beam;

[0040] The multi-band laser light source module 130 is connected to the pump beam combining module 120 and is used to generate target laser beams corresponding to multiple target bands;

[0041] The beam output module 140 is connected to the multi-band laser light source module 130 and is used to split the multiple target laser beams and output the target laser beams corresponding to the target bands respectively;

[0042] Among them, the multi-band laser light source module 130 includes a first multi-core fiber Bragg grating 132, a multi-core double-clad active fiber 134 and a second multi-core fiber Bragg grating 136 connected in sequence. The first multi-core fiber Bragg grating 132 is connected to the pump beam combining module 120, and the second multi-core fiber Bragg grating 136 is connected to the beam output module 140. The number of cores of the multi-core double-clad active fiber 134 is equal to the number of target laser beams. The core of the multi-core double-clad active fiber 134 is doped with rare earth ions, and the rare earth ions are a combination of one or more lanthanide ions. The target band is located within the luminescence band of the rare earth ions.

[0043] Among them, the number of multi-mode pump lasers can be set according to actual conditions and is not limited in the embodiments of the present application; the target band can be set according to actual conditions and is not limited in the embodiments of the present application; the number of target laser beams can be set according to actual conditions and is not limited in the embodiments of the present application. It should be noted that the number of cores of the multi-core double-clad active optical fiber is equal to the number of target laser beams, that is, a single core of the multi-core double-clad active optical fiber corresponds to a target laser beam of a target band.

[0044] Specifically, if Figure 1As shown, the pump excitation module 110 may include multiple light sources for generating multimode pump lasers. The pump excitation module 110 generates multiple multimode pump lasers. The multiple multimode pump lasers are combined into a beam of high-power pump lasers by the pump beam combining module 120. The high-power pump laser enters the multi-band laser light source module 130, wherein the high-power pump laser continuously passes through different cores in the multi-core double-clad active optical fiber 134. Since the cores of the multi-core double-clad active optical fiber 134 are doped with rare earth ions, the rare earth ions doped in each core are different, and the target band is located in the luminous band of the rare earth ions, the high-power pump laser is gradually doped by the different rare earth ions doped in each core. After photoion absorption, a population inversion occurs, and then a stimulated emission process occurs, generating stimulated emission signal light of different bands (target laser beams corresponding to each target band). The stimulated emission signal light of different bands generated is continuously reflected back and forth, oscillated, and amplified in the first multi-core fiber Bragg grating 132 (rear cavity mirror) and the second multi-core fiber Bragg grating 136 (front cavity mirror). Part of the stimulated emission signal light is input to the beam output module 140 through the second multi-core fiber Bragg grating 136 (front cavity mirror). The beam output module 140 has a wavelength demultiplexing function, which enables the stimulated emission signal light of different bands to be port-separated and stably output, that is, the target laser beams corresponding to each target band are output separately.

[0045] It should be noted that the multi-band laser light source module can be a multi-band laser resonant cavity. Under the continuous excitation of high-power pump laser, different rare earth ions (laser working medium) doped in multiple cores in the multi-core double-clad active optical fiber undergo population inversion, generating stimulated radiation signal light of different bands. Under the continuous feedback of the front cavity mirror and the rear cavity mirror in different bands, the signal light in each core oscillates back and forth many times in its respective waveguide structure and is amplified many times, so that the fiber laser can simultaneously and efficiently emit and generate multi-band lasers (target laser beams corresponding to each target band); wherein, the second multi-core fiber Bragg grating (front cavity mirror) is partially reflective, and a portion of the emitted light will be continuously reflected and oscillated back and forth in the multi-band laser resonant cavity, that is, it is amplified, and at the same time a portion of the target laser is used for output.

[0046] The multi-band high-power multi-core fiber laser comprises a pump excitation module, a pump beam combining module, a multi-band laser light source module and a beam output module connected in sequence. The pump beam combining module is used to combine multiple multi-mode pump lasers generated by the pump excitation module into a high-power pump laser. The pump excitation module is used to excite the multi-band laser light source module to generate a plurality of high-power target laser beams corresponding to target bands. The beam output module is used to split the multiple target laser beams and output the target laser beams corresponding to each target band respectively. The multi-band laser light source module comprises a first multi-core fiber Bragg grating, a multi-core double-clad active fiber and a second multi-core fiber Bragg grating connected in sequence. The first multi-core fiber Bragg grating is connected to the pump beam combining module. module, and the second multi-core fiber Bragg grating connected to the beam output module; by utilizing an independent laser waveguide channel structure (multiple cores in a multi-core double-clad active optical fiber) and a rare earth ion-doped core as the laser working medium, the gain competition effect of different bands of lasers in the generation and operation process in the traditional technical solution is avoided; and the compact and integrated multi-band laser resonant cavity (multi-band laser light source module) can avoid interference from the external environment, and can achieve highly reliable multi-band fiber laser lasing and output (outputting the target laser beam corresponding to each target band separately), solving the problems of the conventional single-core multi-band fiber laser, such as complex system structure, small number of working bands, low conversion efficiency, poor reliability and small wavelength interval.

[0047] In one embodiment, a fiber Bragg grating corresponding to a target wavelength band is inscribed on the bare core of the first multi-core fiber Bragg grating;

[0048] The bare core of the second multi-core fiber Bragg grating is inscribed with a fiber Bragg grating corresponding to the target wavelength band.

[0049] Specifically, the first multi-core fiber Bragg grating can be a passive multi-core double-clad optical fiber, after the coating is stripped off at one end, and then a high-reflectivity, broadband grating of different target bands is written point by point at a position close to the same core of the bare fiber through an ultraviolet laser phase mask method or a femtosecond laser direct writing method. It should be noted that the above operation is repeated in sequence on different cores in the first multi-core fiber Bragg grating; the second multi-core fiber Bragg grating can be a passive multi-core double-clad optical fiber, after the coating is stripped off at one end, and then a low-reflectivity, narrow-band grating of different target bands is written point by point at a position close to the same core of the bare fiber through an ultraviolet laser phase mask method or a femtosecond laser direct writing method. The above operation is repeated in sequence on different cores in the second multi-core fiber Bragg grating.

[0050] Exemplarily, the first multi-core fiber Bragg grating can be a cascaded high-reflection multi-core fiber Bragg grating, and the second multi-core fiber Bragg grating can be a cascaded low-reflection multi-core fiber Bragg grating; the cascaded high-reflection multi-core fiber Bragg grating can have a reflectivity greater than 90% for signal light wavelengths of 0.9μm to 1.2μm, 1.5μm to 1.6μm, and 1.7μm to 2.2μm, and its reflection spectrum 3dB bandwidth range is 1nm to 10nm, and the transmittance to the pump light wavelength is greater than 95%; The cascaded low-reflection multi-core fiber Bragg grating can achieve a reflectivity range of 5% to 70% for signal light wavelengths in the 0.9μm to 1.2μm, 1.5μm to 1.6μm, and 1.7μm to 2.2μm bands. The 3dB bandwidth of its reflection spectrum is less than 1nm. That is, the cascaded low-reflection multi-core fiber Bragg grating (front cavity mirror) is partially reflective, and a portion of the emitted light will be continuously reflected and oscillated back and forth in the multi-band laser resonant cavity, that is, it is amplified, while a portion of the light is used for output.

[0051] In an embodiment of the present application, a fiber Bragg grating (FBG) corresponding to a target wavelength band is inscribed on the bare core of a first multi-core fiber Bragg grating, and a fiber Bragg grating (FBG) corresponding to a target wavelength band is inscribed on the bare core of a second multi-core fiber Bragg grating. When and only when the broadband fiber Bragg grating and narrowband fiber Bragg grating pair on a certain fiber core satisfy center wavelength matching (the wavelength of the fiber Bragg grating inscribed on the bare core of the first multi-core fiber Bragg grating is equal to that of the fiber Bragg grating inscribed on the bare core of the second multi-core fiber Bragg grating), and at the same time, the center wavelength corresponding to the fiber Bragg grating is within the luminescence wavelength band of the rare earth ions doped in this fiber core, the multi-band laser light source module can oscillate and emit laser light of the corresponding working band, thereby avoiding the tedious processes of axial positioning and precise distinction of multiple fiber core positions required during the fiber Bragg grating pair inscription and connection of the multi-band laser light source module, thereby reducing the production cost of the fiber laser.

[0052] In one embodiment, the reflectivity and 3dB bandwidth of the second multi-core fiber Bragg grating for the target laser beam are smaller than those of the first multi-core fiber Bragg grating for the target laser beam.

[0053] Specifically, the second multi-core fiber Bragg grating (front cavity mirror) is partially reflective, and a portion of the emitted stimulated radiation signal light of different bands will be continuously reflected and oscillated back and forth in the multi-band laser light source module (multi-band laser resonant cavity), that is, it is amplified, and the target laser beam is obtained. Because the reflectivity and reflection spectrum 3dB bandwidth of the second multi-core fiber Bragg grating for the target laser beam are smaller than the reflectivity and reflection spectrum 3dB bandwidth of the first multi-core fiber Bragg grating for the target laser beam, part of the target laser beam is not reflected by the second multi-core fiber Bragg grating, but is output to the beam output module, and then the target laser beams corresponding to each target band are output respectively.

[0054] In the embodiment of the present application, the reflectivity and 3dB bandwidth of the reflection spectrum of the second multi-core fiber Bragg grating for the target laser beam are smaller than the reflectivity and 3dB bandwidth of the reflection spectrum of the first multi-core fiber Bragg grating for the target laser beam, so that the stimulated radiation signal light of different bands is continuously reflected and oscillated back and forth in the multi-band laser light source module, and the amplified part of the target laser beam is not reflected by the second multi-core fiber Bragg grating, but is output to the beam output module, and then the target laser beams corresponding to each target band are output respectively.

[0055] In one embodiment, the lanthanide ions include Nd 3+ 、Yb 3+ 、Er 3+ 、Tm 3+ and Ho 3+ ; The doping concentration of rare earth ions is greater than 1wt%.

[0056] Specifically, the rare earth ion can be single-doped Yb 3+ , co-doped Er 3+ and Yb 3+ , co-doped Tm 3+ and Yb 3+ , co-doped with Ho 3+ and Yb 3+ Two, three, four or other combinations, or single doping with Nd 3+ , co-doped Er 3+ and Nd 3+ , co-doped Tm 3+ and Nd 3+ , co-doped with Ho 3+ and Nd 3+ When the doping concentration of rare earth ions is greater than 1wt%, a better luminescence effect can be achieved, that is, the generated stimulated radiation signal light is stronger and the conversion efficiency is higher, which is convenient for improving the output power of the fiber laser.

[0057] It is understood that the above-mentioned rare earth ions may also be other ions, and are not limited to the lanthanide ions mentioned in the above embodiments, as long as they can achieve the function of achieving the population inversion of different rare earth ions (laser working medium) doped in multiple fiber cores in a multi-core double-clad active optical fiber under continuous excitation of a high-power pump laser, thereby generating stimulated emission signal light of different bands.

[0058] In the embodiments of the present application, by utilizing rare-earth ion-doped optical fibers as the laser working medium, an independent laser waveguide channel structure is provided, enabling different fiber cores to simultaneously achieve efficient lasing and generation of multiple wavelength lasers (target laser beams corresponding to multiple target wavelengths) through different rare-earth ion-doped regions. Compared to multi-band (wavelength) fiber lasers that directly lased within the same or similar gain intervals of a single-core working medium, this avoids the mode competition effect and addresses the challenges of conventional single-core multi-band (wavelength) fiber lasers, such as small wavelength spacing, low output power, and poor reliability. Furthermore, by setting the rare-earth ion doping concentration to greater than 1wt%, the output power of the fiber laser is increased.

[0059] In one embodiment, Figure 2 As shown, the shape of each core in the multi-core double-clad active optical fiber is a circle with equal or unequal diameters, the circle includes a first circle and a second circle, the distance between the center of the first circle and the center of the second circle is a first value, the sum of the radius of the first circle and the radius of the second circle is a second value, and the first value is greater than or equal to a preset multiple of the second value;

[0060] The inner cladding shapes of multi-core double-clad active optical fibers include rectangle, hexagon, octagon or dodecagon.

[0061] Among them, the diameter range and numerical aperture of the core of the multi-core double-clad active optical fiber can be set according to actual conditions. In the embodiment of the present application, the core diameter range is 4 μm to 40 μm and the numerical aperture range is 0.03 to 0.3 as an example for explanation; the diameter range of the inner cladding of the multi-core double-clad active optical fiber can be set according to actual conditions. In the embodiment of the present application, the diameter range of the inner cladding of the multi-core double-clad active optical fiber is 200 μm to 800 μm as an example for explanation; the preset multiple can be set according to actual conditions. In the embodiment of the present application, the preset multiple is 2 times as an example for explanation.

[0062] Specifically, Figure 2 Schematic diagrams of multi-core double-clad active optical fibers including different numbers of cores when the inner cladding shape of the multi-core double-clad active optical fiber is a dodecagon are shown as examples. (a) represents the multi-core double-clad active optical fiber with 2 cores, (b) represents the multi-core double-clad active optical fiber with 3 cores, (c) represents the multi-core double-clad active optical fiber with 4 cores, (d) represents the multi-core double-clad active optical fiber with 5 cores, (e) represents the multi-core double-clad active optical fiber with 6 cores, and (f) represents the multi-core double-clad active optical fiber with 7 cores, wherein, Figure 251 represents the core of the multi-core double-clad active optical fiber, and 52 represents the inner cladding of the multi-core double-clad active optical fiber. The multiple cores in the multi-core double-clad active optical fiber are in the shape of circles with equal or unequal diameters, and the distance between the centers of the two circles is greater than or equal to twice the sum of the radii of the two circles.

[0063] It is understandable that the inner cladding shape of the multi-core double-clad active optical fiber can also be other shapes, not limited to the shapes mentioned in the above embodiments, as long as it is not a circularly symmetrical structure, because the circular inner cladding has low absorption of high-power pump laser.

[0064] In the embodiment of the present application, multiple cores of a rare earth ion-doped multi-core double-clad optical fiber share an inner cladding to form a compact, integrated multi-band laser resonant cavity, further improving the conversion efficiency and output power level of the fiber laser.

[0065] In one embodiment, Figure 3 As shown, the pump excitation module includes multiple multimode pump light sources 1, the output end of each multimode pump light source 1 is connected to the pump beam combining module, and the working wavelength of the multimode pump light source is associated with the type of rare earth ions.

[0066] The multimode pump light source 1 may be a pigtailed multimode solid-state laser, a semiconductor laser, or a fiber laser, with a power greater than 1W.

[0067] Specifically, if Figure 3 As shown, the operating wavelength range of the single-core beam (pump light) output by the multimode pump light source 1 is 780nm to 820nm or 910nm to 1020nm. The specific operating wavelength of the single-core beam is selected according to the rare earth ion doping type (type of rare earth ions) of the gain fiber.

[0068] It is understandable that the multimode pump light source may also be other devices, not limited to the devices mentioned in the above embodiments, as long as it can achieve the function of outputting a single-core light beam.

[0069] In one embodiment, Figure 3 As shown, the pump combining module includes a pump combiner 2, the input end of the pump combiner 2 is connected to the output end of the pump excitation module, and the output end of the pump combiner 2 is connected to the first multi-core fiber Bragg grating 3;

[0070] The input end of the pump combiner 2 is a plurality of multimode optical fibers whose core diameters are in a first numerical range, and the output end of the pump combiner 2 is a multimode optical fiber whose core diameter is in a second numerical range, or a passive double-clad optical fiber whose inner cladding diameter is in the second numerical range, and the second numerical range is greater than or equal to the first numerical range.

[0071] For example, both the first numerical range and the second numerical range can be set according to actual conditions. In the embodiment of the present application, the first numerical range is 50 μm to 200 μm and the second numerical range is 200 μm to 800 μm as an example for illustration.

[0072] Specifically, if Figure 3 As shown, the pump combiner 2 can be in the form of N×1 ports, where N is the number of pump ports (N is greater than or equal to 2, and N is equal to the number of multimode pump light sources 1). N thin-core multimode optical fibers with core diameters ranging from 50 μm to 200 μm are used as input ends of the pump combiner 2; and one thick-core multimode optical fiber with a core diameter ranging from 200 μm to 800 μm or a passive single-core double-clad optical fiber with an inner cladding diameter ranging from 200 μm to 800 μm is used as the output end of the pump combiner 2.

[0073] In one embodiment, Figure 3 As shown, the light beam output module includes a cladding light filter 6 and a wave splitter 7 connected in sequence, and the cladding light filter 6 is also connected to the second multi-core fiber Bragg grating 4.

[0074] in, Figure 3 The reference numeral 5 indicates a multi-core double-clad active optical fiber.

[0075] Specifically, the cladding light filter 6 can filter out the cladding light in the target laser beam to prevent the waste heat generated from being too concentrated and affecting the reliability of the fiber laser. The wavelength splitter 7 can have a wavelength demultiplexing function to achieve port separation and stable output of stimulated radiation signal light (target laser beam) of different bands, that is, output the target laser beam corresponding to each target band separately.

[0076] In one embodiment, the cladding light filter is a passive double-clad optical fiber, and a preset area within the cladding light filter is coated with multiple layers of UV glue arranged from low to high refractive index along the direction from the input end to the output end of the cladding light filter, and the refractive index of each UV glue is greater than the refractive index of the inner cladding of the optical fiber of the cladding light filter.

[0077] Among them, the range of the preset area can be set according to actual conditions. In the embodiment of the present application, the length of the preset area is 0.5 cm to 10 cm as an example for illustration; the number of layers of UV glue can be set according to actual conditions, generally set to greater than or equal to 2, to enhance the filtering effect of cladding light.

[0078] Specifically, the cladding light filter is a passive double-clad optical fiber. The coating layer of the middle of the passive double-clad optical fiber is stripped with a length of about 0.5 cm to 10 cm. The bare fiber area is directly coated, or after the inner cladding of the optical fiber is etched with hydrofluoric acid to a preset thickness (set according to actual conditions), different UV glues with refractive indices arranged in a gradient from low to high (along the direction from the input end to the output end of the cladding light filter) are coated. It should be noted that the refractive index of the UV glue is greater than the refractive index of the inner cladding of the optical fiber.

[0079] In the embodiment of the present application, a multi-layer UV adhesive with a gradient refractive index is coated on a preset area within the cladding light filter to gradually and evenly filter out the cladding light, thereby preventing the waste heat generated from being too concentrated and affecting the reliability of the fiber laser.

[0080] In one embodiment, the input end of the wavelength splitter is a passive double-clad optical fiber, and the output end of the wavelength splitter is a plurality of passive single-clad optical fibers.

[0081] Specifically, the wavelength splitter is in the form of 1×n ports, where n is the number of output ports (n is greater than or equal to 2, and n is equal to the number of target laser beams). The wavelength splitter is made by drawing n passive single-core single-clad optical fibers into a double-cone shape through a fusion taper process. After the cone area is precisely cut, the cores are precisely aligned and fused with a passive multi-core double-clad optical fiber.

[0082] For example, the wavelength demultiplexing function of the splitter is used to separate and stabilize the laser output of multiple wavelength bands of the fiber laser. The result is a high-power fiber laser that operates simultaneously in the 0.9μm to 1.2μm, 1.5μm to 1.6μm, and 1.7μm to 2.2μm bands, with near-diffraction-limited output.

[0083] To facilitate understanding by those skilled in the art, the fiber laser in the embodiment of the present application is described below with reference to a specific example:

[0084] The multimode pump light source is a pigtailed multimode semiconductor laser with a wavelength of 976nm and a power of 150W. The N×1 pump combiner is a 3×1 port, with three multimode optical fibers with a core diameter of 105μm as the pump input and a passive single-core double-clad optical fiber with an inner cladding diameter of 250μm as the output. The cascaded high-reflection multi-core fiber Bragg grating (first multi-core fiber Bragg grating) and the cascaded low-reflection multi-core fiber Bragg grating (second multi-core fiber Bragg grating) are constructed by stripping the coating of two passive multi-core double-clad optical fibers. Then, using an ultraviolet laser phase mask method, fiber Bragg gratings with signal light wavelengths of 1030nm, 1535nm, and 1850nm (target band) are inscribed point by point at similar locations on the same core of the bare fibers. The cascaded high-reflection multi-core fiber Bragg gratings have a transmittance of 99.9% for 976nm pump light (high-power pump laser) and a reflectivity of 99.9% for signal light wavelengths of 1030nm, 1535nm, and 1850nm (target band), with a 3dB bandwidth of 2nm for both. The cascaded low-reflection multi-core fiber Bragg gratings have a reflectivity of 15% for signal light wavelengths of 1030nm, 1535nm, and 1850nm (target band), with a 3dB bandwidth of 0.3nm for both.

[0085] The number of cores of the rare earth ion doped multi-core double-clad optical fiber is 3, and the three core regions are uniformly doped with Yb 3+ , co-doped Er 3+ and Yb 3+ , co-doped Tm 3+ and Yb 3+ ; The rare earth ion doping concentration of the three cores is: 5wt% Yb 3+ , 2wt% Er 3+ and 4wt% Yb 3+ , 2wt% Tm 3+ and 5wt% Yb 3+ The three cores are circular with varying diameters, with the distances between their centers being 19μm, 19μm, and 18μm, respectively. The core diameters are 10μm, 9μm, and 10μm, respectively, with numerical apertures of 0.09 (both the core diameter and numerical aperture are related to the target wavelength band). The inner cladding of the rare-earth ion-doped multi-core double-clad optical fiber is a dodecagon with a diameter of 250μm. The cladding stripper (cladding filter) removes approximately 2cm of the coating from the middle of a passive multi-core double-clad optical fiber. The bare fiber region is directly coated with two types of UV adhesive with varying refractive indices, from low to high, along the input to output direction. The wavelength splitter is a 1×3 port type, separating and outputting the 1030nm, 1535nm, and 1850nm signal light wavelengths (target wavelength bands), respectively.

[0086] The pump light (single-core beam) emitted by three multimode pump light sources with a wavelength of 976nm and a power of 150W is coupled into the multi-band laser resonant cavity from one end of the cascaded high-reflection multi-core fiber Bragg grating (back cavity mirror) through a 3×1 pump combiner. Under the continuous pumping of the multimode pump light source, the three rare earth ion-doped fiber cores (laser working medium) continuously pass through the three fiber cores and are gradually absorbed by the different rare earth luminescent ions doped in the three fiber cores, forming a particle number inversion, and then the stimulated The radiation process generates stimulated emission signal light of three wavelength bands. Under the multiple feedback effects of the front and rear cavity mirrors of the three wavelength bands, the signal light in the three fiber cores oscillates back and forth many times and is amplified many times, so that the fiber laser simultaneously and efficiently emits and generates three wavelength bands of laser light of 1030nm, 1535nm, and 1850nm (the target laser beam corresponding to the target wavelength band); and then the wavelength demultiplexing function of the 1×3 splitter is used to enable the fiber laser to achieve multi-port separation and stable output of the three wavelength bands. Finally, 1030nm, 1535nm, and 1850nm can be obtained to work simultaneously, with output powers of 200W, 100W, and 180W respectively, and the beam quality factor M 2 The output spectrum of the fiber laser is 1.15. Figure 4 shown.

[0087] To facilitate understanding by those skilled in the art, the fiber laser in the embodiment of the present application is described below with reference to another specific example:

[0088] The multimode pump light source is a pigtailed multimode semiconductor laser with an optical wavelength of 808nm and a power of 60W. The N×1 pump combiner is a 7×1 port configuration, using seven multimode fibers with a core diameter of 105μm as the pump input and a passive single-core double-clad fiber with an inner cladding diameter of 300μm as the output. The cascaded high-reflection multi-core fiber Bragg grating (first multi-core fiber Bragg grating) and the cascaded low-reflection multi-core fiber Bragg grating (second multi-core fiber Bragg grating) are constructed by stripping the coating of two passive multi-core double-clad fibers, and then inscribing fiber Bragg gratings with signal wavelengths of 930nm, 1560nm, and 2100nm (target wavelength bands) point by point on the same core of the bare fiber using femtosecond laser direct writing. The transmittance of the cascaded high-reflection multi-core fiber Bragg grating for 808nm pump light (high-power pump laser) is 99.9%, and the reflectivity for signal light wavelengths of 930nm, 1560nm, and 2100nm (target band) is 99.9%. The 3dB bandwidth of its reflection spectrum is 2nm. The reflectivity of the cascaded low-reflection multi-core fiber Bragg grating for signal light wavelengths of 930nm, 1560nm, and 2100nm (target band) is 20%, and the 3dB bandwidth of its reflection spectrum is 0.4nm.

[0089] The number of cores of the rare earth ion doped multi-core double-clad optical fiber is 3, and the three core regions are uniformly doped with Nd 3+ , co-doped Er 3+ and Nd 3+ , co-doped with Ho 3+ and Nd 3+ ; The rare earth ion doping concentration of the three cores is: 3wt% Nd 3+ 、1wt%Er 3+ and 2.5wt% Nd 3+ 、1.5wt%Ho 3+ and 4wt% Nd 3+ . The three cores are circular with different diameters, and the distances between the centers of the two circles are 22μm, 22μm and 20μm respectively. The core diameters are 12μm, 10μm and 10μm respectively, and the numerical apertures are all 0.08 (the core diameter and numerical aperture are both related to the target band); the inner cladding shape of the rare earth ion doped multi-core double-clad optical fiber is a dodecagon, and the inner cladding diameter is 300μm. Among them, the cladding light stripper (cladding light filter) is a passive multi-core double-clad optical fiber with a coating stripping length of about 3cm in the middle. Along the direction from the input end to the output end, the bare fiber area is directly coated with three kinds of UV glue with low to high refractive index. Among them, the wavelength splitter is a 1×3 port type, which separates and outputs the 930nm, 1560nm and 2100nm signal light wavelengths (target bands) respectively.

[0090] Pump light (single-core beams) from seven multimode pump sources with a wavelength of 808 nm and a power of 60 W is coupled into the multi-band laser resonator through a 7×1 pump combiner and coupled from one end of a cascaded high-reflection multi-core fiber Bragg grating (FBG) (rear cavity mirror). Under continuous pumping from the pump source, the high-power pump laser light continuously travels through the three rare-earth ion-doped fiber cores (the laser working medium). This high-power pump laser light is gradually absorbed by the different rare-earth luminescent ions doped in the three cores, causing population inversion and stimulated emission. This generates stimulated emission signal light in three wavelength bands. Multiple feedback from the front and rear cavity mirrors of the three wavelength bands causes the signal light in the three cores to oscillate back and forth and be amplified multiple times, enabling efficient simultaneous lasing and generation of three wavelength bands (930 nm, 1560 nm, and 2100 nm, corresponding to the target laser beams). The wavelength demultiplexing function of a 1×3 splitter is then used to achieve multi-port separation and stable output of the three wavelength bands. Finally, 930nm, 1560nm, and 2100nm can be operated simultaneously, with output powers of 150W, 80W, and 150W respectively, and beam quality factor M 2 The output spectrum of the fiber laser is 1.15. Figure 5 shown.

[0091] It should be noted that the fiber laser structure provided in the embodiments of the present application is also applicable to different numbers of pump light sources, output powers, pump wavelengths, pumping modes, and other parameters such as the type of gain fiber doping ions, doping concentrations, number of fiber cores, core diameters, and operating lengths. As mentioned above, the above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of its implementation.

[0092] In the description of this specification, reference to the terms "some embodiments" or "other embodiments" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example.

[0093] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0094] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

Claims

1. A multi-band high-power multi-core fiber laser, characterized in that: include: A pump excitation module for generating multiple multi-mode pump lasers; A pump beam combining module, connected to the pump excitation module, for combining multiple multi-mode pump light sources into a high-power pump laser beam; A multi-band laser light source module is connected to the pump beam combining module, and is used to generate target laser beams corresponding to multiple target bands; A beam output module, connected to the multi-band laser light source module, for splitting the multiple target laser beams and outputting the target laser beams corresponding to the target bands respectively; The multi-band laser light source module comprises a first multi-core fiber Bragg grating, a multi-core double-clad active fiber, and a second multi-core fiber Bragg grating connected in sequence, the first multi-core fiber Bragg grating is connected to the pump beam combining module, the second multi-core fiber Bragg grating is connected to the beam output module, the number of cores of the multi-core double-clad active fiber is equal to the number of the target laser beam, the core of the multi-core double-clad active fiber is doped with rare earth ions, the rare earth ions are a combination of one or more lanthanide ions, and the target band is within the luminescence band of the rare earth ions; The cores in the multi-core double-clad active optical fiber are shaped like circles with equal or unequal diameters, the circles including a first circle and a second circle, the distance between the center of the first circle and the center of the second circle being a first value, the sum of the radius of the first circle and the radius of the second circle being a second value, and the first value being greater than or equal to a preset multiple of the second value; The inner cladding shape of the multi-core double-clad active optical fiber includes a rectangle, a hexagon, an octagon or a dodecagon; The pump combining module includes a pump combiner, the input end of the pump combiner is connected to the output end of the pump excitation module, and the output end of the pump combiner is connected to the first multi-core fiber Bragg grating; The input end of the pump combiner is a plurality of multimode optical fibers whose core diameters are in a first numerical range, and the output end of the pump combiner is a multimode optical fiber whose core diameter is in a second numerical range, or a passive double-clad optical fiber whose inner cladding diameter is in the second numerical range, and the second numerical range is greater than or equal to the first numerical range.

2. The multi-band high-power multi-core fiber laser according to claim 1, characterized in that: The bare core of the first multi-core fiber Bragg grating is engraved with a fiber Bragg grating corresponding to the target wavelength band; The bare core of the second multi-core fiber Bragg grating is inscribed with a fiber Bragg grating corresponding to the target wavelength band.

3. The multi-band high-power multi-core fiber laser according to claim 2, characterized in that: The reflectivity and 3dB bandwidth of the reflection spectrum of the second multi-core fiber Bragg grating for the target laser beam are both smaller than those of the first multi-core fiber Bragg grating for the target laser beam.

4. The multi-band high-power multi-core fiber laser according to claim 1, characterized in that: The lanthanide ions include Nd 3+ 、Yb 3+ 、Er 3+ 、Tm 3+ and Ho 3+ ; The doping concentration of the rare earth ions is greater than 1wt%.

5. The multi-band high-power multi-core fiber laser according to claim 1, characterized in that: The pump excitation module includes a plurality of multi-mode pump light sources, the output end of each pump light source is connected to the pump beam combining module, and the operating wavelength band of the multi-mode pump laser is associated with the type of the rare earth ions.

6. The multi-band high-power multi-core fiber laser according to claim 1, characterized in that: The light beam output module includes a cladding light filter and a wave splitter connected in sequence, and the cladding light filter is also connected to the second multi-core fiber Bragg grating.

7. The multi-band high-power multi-core fiber laser according to claim 6, characterized in that: The cladding light filter is a passive double-clad optical fiber. A preset area within the cladding light filter is coated with multiple layers of UV glue whose refractive index is arranged from low to high along the direction from the input end of the cladding light filter to the output end of the cladding light filter. The refractive index of each UV glue is greater than the refractive index of the inner cladding of the optical fiber of the cladding light filter.

8. The multi-band high-power multi-core fiber laser according to claim 6, characterized in that: The input end of the wave splitter is a passive double-clad optical fiber, and the output end of the wave splitter is a plurality of passive single-clad optical fibers.

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