Multi-band high-power multi-core fiber laser

Abstract

The invention relates to a multi-band high-power multi-core fiber laser which comprises a pumping excitation module, a pumping beam combining module, a multi-band laser light source module and a light beam output module which are connected in sequence, and the pumping beam combining module is used for combining a plurality of multi-mode pumping lasers generated by the pumping excitation module into a beam of high-power pumping laser. The multi-band laser light source module is used for generating target laser beams corresponding to a plurality of target bands, and the light beam output module is used for carrying out wave division on the plurality of target laser beams and respectively outputting the target laser beams corresponding to the target bands, 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 which are connected in sequence, the first multi-core fiber bragg grating is connected with the pumping beam combining module, and the second multi-core fiber bragg grating is connected with the light beam output module; the optical fiber laser can solve the problems that the number of working wavebands of the optical fiber laser is small, the wavelength interval is small and the output power is low.

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 optical fiber laser. Background Art

[0002] At present, fiber lasers capable of multi-band output often use single-core rare earth ion-doped optical fiber as the laser working medium, and combine multiple frequency selection 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, resulting in 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, used to generate multiple multi-mode pump lasers;

[0007] A pump beam combining module is connected to the pump excitation module. The pump beam combining module 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, and the multi-band laser light source module is used to generate target laser beams corresponding to multiple target bands;

[0009] A beam output module is connected to the multi-band laser light source module, and the beam output module is used to split multiple target laser beams and output 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 grating, a multi-core double-clad active fiber and a second multi-core fiber grating which are connected in sequence, the first multi-core fiber grating is connected to a pump beam combining module, the second multi-core fiber 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, the rare earth ions are a combination of one or more lanthanide ions, and 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 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.

[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 a plurality of pump light sources, the output end of each pump light source is connected to the pump beam combining module, and the working band of the multi-mode pump laser is associated with the type of rare earth ions.

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

[0019] The input end of the pump combiner is a plurality of multimode optical fibers with core diameters in a first numerical range, and the output end of the pump combiner is a multimode optical fiber with a core diameter in a second numerical range, or a passive double-clad optical fiber with an inner cladding diameter in 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 also connected to a second multi-core fiber 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 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, 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, wherein the pump beam combining module is used to combine a plurality of multi-mode pump lasers generated by the pump excitation module into a beam of high-power pump lasers, the pump excitation module is used to excite the multi-band laser light source module to generate a plurality of target laser beams corresponding to target bands, and the beam output module is used to split the plurality of target laser beams and output the target laser beams corresponding to the target bands respectively, 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 double-clad active optical fiber connected in sequence The invention relates to a multi-core fiber grating, a first multi-core fiber grating is connected to a pump beam combining module, and a second multi-core fiber grating is connected to a beam output module; since the number of cores of the multi-core double-clad active optical fiber is equal to the number of target laser beams, and the cores of the multi-core double-clad active optical fiber are doped with rare earth ions as laser working media, different 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 lasers, the mode competition effect is avoided, and the problems of the existing fiber lasers having a small number of working bands, a small wavelength interval and a low output power are solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the conventional technology, the drawings required for use in the embodiments or the conventional technology descriptions are briefly introduced below. 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] FIG1 is a block diagram of a multi-band high-power multi-core fiber laser according to an embodiment;

[0026] FIG2 is a schematic diagram of the shapes of multiple cores of a multi-core double-clad active optical fiber in one embodiment;

[0027] FIG3 is a schematic diagram of the structure of a multi-band high-power multi-core fiber laser in one embodiment;

[0028] FIG4 is an output spectrum diagram of a multi-band high-power multi-core fiber laser in one embodiment;

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

[0030] In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. Embodiments of the present application are provided in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is 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 generally understood by those skilled in the art of the technical field of the present application. The terms used herein in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. It is understood that the terms "first", "second", etc. used in the present application can be used to describe various elements in this article, but these elements are not limited by these terms. These terms are only used to distinguish a first element from another element.

[0032] When used herein, the singular forms "a", "an", and "said / the" may also include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "include / comprise" or "have" and the like specify the presence of stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not exclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. At the same time, the term "and / or" 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 multi-band simultaneous 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 lasers of different bands or different wavelengths in the same band (with small wavelength intervals). For example, using a single-core Er 3+ Doped ZBLAN (ZrF 4 -BaF 2 -LaF 3 -AlF 3-NaF) double-clad fiber and two sets of front and rear 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 is constructed by co-doped single-clad optical fiber and dual-channel narrowband polarization-maintaining fiber Bragg grating, which realizes the simultaneous output of four wavelengths of laser at 1548.91nm, 1549.31nm, 1549.73nm, and 1550.13nm, with a power of about 4.5mW. However, due to the direct lasing using the same or similar gain range (within the same band) of the laser working medium, there is mode competition between the wavelengths in the cavity, resulting in a small wavelength interval, low output power, and poor reliability of the fiber laser.

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

[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 target laser beams, 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 grating (rear cavity mirror) and the second multi-core fiber 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 to generate 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 of the multi-core double-clad active optical fiber oscillates back and forth many times in their respective waveguide structures and is amplified many times, so that the pump excitation module can simultaneously efficiently laser and generate multi-band lasers (target laser beams corresponding to multiple target bands), and then use the beam output module to split the multiple target laser beams, so that the multi-band lasers of the multi-core fiber laser (target laser beams corresponding to multiple target bands) can achieve port separation and stable output.

[0037] In an exemplary embodiment, as shown in FIG1 , a multi-band high-power multi-core fiber laser 100 is provided, comprising:

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

[0039] A pump beam combining module 120 is connected to the pump excitation module 110, and the pump beam combining module 120 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 the multi-band laser light source module 130 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. The beam output module 140 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 grating 132, a multi-core double-clad active fiber 134 and a second multi-core fiber grating 136 which are connected in sequence, the first multi-core fiber grating 132 is connected to the pump beam combining module 120, the second multi-core fiber 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, the rare earth ions are a combination of one or more lanthanide ions, and the target band is located in the luminescent 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, as shown in FIG. 1 , the pump excitation module 110 may include a plurality of light sources for generating multimode pump lasers. The pump excitation module 110 generates a plurality of multimode pump lasers. The plurality of 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 emission 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 the rare earth luminescent ions are absorbed, a particle number inversion is formed, and then a stimulated radiation process occurs, generating stimulated radiation signal lights of different bands (target laser beams corresponding to each target band). The generated stimulated radiation signal lights of different bands are continuously reflected, oscillated and amplified back and forth in the first multi-core fiber grating 132 (rear cavity mirror) and the second multi-core fiber grating 136 (front cavity mirror). Part of the stimulated radiation signal lights is input to the beam output module 140 through the second multi-core fiber grating 136 (front cavity mirror). The beam output module 140 has a wavelength demultiplexing function, so that the stimulated radiation signal lights of different bands can be port separated and stably output, that is, the target laser beams corresponding to each target band are output respectively.

[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 a high-power pump laser, different rare earth ions (laser working medium) doped in multiple cores in a multi-core double-clad active optical fiber undergo a 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 simultaneously and efficiently emits and generates multiple-band lasers (target laser beams corresponding to each target band); wherein, the second multi-core fiber 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, wherein 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 high-power target laser beam corresponding to multiple target bands, and 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, wherein the multi-band laser light source module comprises a first multi-core fiber grating, a multi-core double-clad active fiber and a second multi-core fiber grating connected in sequence, and the first multi-core fiber grating is connected to the pump beam combining module. module, and the second multi-core fiber 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 a laser working medium, the gain competition effect of lasers of different bands in the generation and working 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 high-reliability multi-band fiber laser lasing and output (outputting the target laser beams corresponding to each target band respectively), solving the problems of complex system structure, small number of working bands, low conversion efficiency, poor reliability and small wavelength interval of conventional single-core multi-band fiber lasers.

[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 grating can be a passive multi-core double-clad optical fiber, after the coating is stripped off at one end, 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 by 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 grating; the second multi-core fiber grating can be a passive multi-core double-clad optical fiber, after the coating is stripped off at one end, 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 by 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 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 in the range of 0.9 μm to 1.2 μm, 1.5 μm to 1.6 μm, and 1.7 μm to 2.2 μm, 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 have a reflectivity range of 5% to 70% for signal light wavelengths in the range of 0.9μm to 1.2μm, 1.5μm to 1.6μm, and 1.7μm to 2.2μm, and its reflection spectrum 3dB bandwidth is less than 1nm, that is, the cascaded low-reflection multi-core fiber Bragg grating (front cavity mirror) is partially reflective, and a part 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 part of the light is used for output.

[0051] In the embodiment of the present application, by engraving a fiber Bragg grating corresponding to the target band on the bare core of the first multi-core fiber Bragg grating, and engraving a fiber Bragg grating corresponding to the target band on the bare core of the 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 the central wavelength matching (the wavelength of the fiber Bragg grating engraved on the bare core of the first multi-core fiber Bragg grating is equal to that of the fiber Bragg grating engraved on the bare core of the second multi-core fiber Bragg grating), and at the same time, the central wavelength corresponding to the fiber Bragg grating is in the luminescent band of the rare earth ions doped in this fiber core, the multi-band laser light source module can oscillate and emit laser of the corresponding working band, thereby avoiding the cumbersome processes of axial positioning and precise distinction of multiple fiber core positions required during the writing of the fiber Bragg grating pair and the 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 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.

[0053] Specifically, the second multi-core fiber grating (front cavity mirror) is partially reflective, and a part 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 grating for the target laser beam are smaller than the reflectivity and reflection spectrum 3dB bandwidth of the first multi-core fiber grating for the target laser beam, part of the target laser beam is not reflected by the second multi-core fiber 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 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, 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 with 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 with 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 understandable 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 causing the different rare earth ions (laser working medium) doped in multiple cores of a multi-core double-clad active optical fiber to undergo population inversion under the continuous excitation of a high-power pump laser and generate stimulated radiation signal light of different bands.

[0058] In the embodiment of the present application, by using rare earth ion doped optical fiber as the laser working medium, an independent laser waveguide channel structure is provided, so that different fiber cores can simultaneously realize the efficient lasing and generation of multiple band lasers (target laser beams corresponding to multiple target bands) through different rare earth ion doping regions. Compared with the multi-band (wavelength) optical fiber laser that directly lases in the same or similar gain interval of the single-core working medium, the mode competition effect is avoided, and the problems of small wavelength interval, low output power, and poor reliability of the conventional single-core multi-band (wavelength) optical fiber laser are solved, and the output power of the optical fiber laser is increased by setting the doping concentration of rare earth ions to be greater than 1wt%.

[0059] In one embodiment, as shown in FIG. 2 , 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 4μm to 40μm 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 200μm to 800μm 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, FIG2 exemplarily shows 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, (a) represents the number of cores of the multi-core double-clad active optical fiber as 2, (b) represents the number of cores of the multi-core double-clad active optical fiber as 3, (c) represents the number of cores of the multi-core double-clad active optical fiber as 4, and (d) represents the number of cores of the multi-core double-clad active optical fiber as (e) represents the number of cores of the multi-core double-clad active optical fiber is 6, (f) represents the number of cores of the multi-core double-clad active optical fiber is 7, wherein 51 in FIG2 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 shapes of the multiple cores in the multi-core double-clad active optical fiber are 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 can be understood 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 the 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, as shown in FIG3 , the pump excitation module includes a plurality of 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 multi-mode pump light source 1 may be a pigtailed multi-mode solid-state laser, a semiconductor laser, or a fiber laser, with a power greater than 1W.

[0067] Specifically, as shown in FIG3 , the operating wavelength range of the single-core light beam (pump light) output by the multimode pump light source 1 is 780 nm to 820 nm or 910 nm to 1020 nm, and the specific operating wavelength of the single-core light beam is selected according to the rare earth ion doping type (type of rare earth ions) of the gain fiber.

[0068] It can be understood that the multi-mode pump light source can also be other devices, not limited to the devices mentioned in the above embodiments, as long as the function of outputting a single-core light beam can be achieved.

[0069] In one embodiment, as shown in FIG3 , the pump beam combining module includes a pump beam combiner 2 , the input end of the pump beam combiner 2 is connected to the output end of the pump excitation module, and the output end of the pump beam combiner 2 is connected to the first multi-core fiber grating 3 ;

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

[0071] Exemplarily, 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, as shown in Figure 3, 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), and N thin-core multimode optical fibers with core diameters ranging from 50μm to 200μm are used as the input end of the pump combiner 2; a thick-core multimode optical fiber with a core diameter ranging from 200μm to 800μm or a passive single-core double-clad optical fiber with an inner cladding diameter ranging from 200μm to 800μm is used as the output end of the pump combiner 2.

[0073] In one embodiment, as shown in FIG. 3 , 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 grating 4 .

[0074] Wherein, 5 in FIG. 3 represents 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 avoid excessive concentration of waste heat that affects 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, to output the target laser beams corresponding to each target band respectively.

[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 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, 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 explanation; 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 on the cladding light.

[0078] Specifically, the cladding light filter is a passive double-clad optical fiber, the coating layer of which is stripped in the middle with a length of about 0.5 cm to 10 cm, and 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 of the cladding light filter 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 glue 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 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, and after precisely cutting the cone area, 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 achieve port separation and stable output of multiple wavelength bands of the fiber laser. Finally, a high-power fiber laser with near-diffraction-limited output and simultaneous operation of 0.9μm to 1.2μm, 1.5μm to 1.6μm and 1.7μm to 2.2μm wavelength bands is obtained.

[0083] To facilitate the understanding of 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 form, which uses three multimode optical fibers with a core diameter of 105μm as the pump input end and a passive single-core double-clad optical fiber with an inner cladding diameter of 250μm as the output end. Among them, 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 obtained by stripping the coating of two passive multi-core double-clad optical fibers respectively, and then writing fiber Bragg gratings of 1030nm, 1535nm, and 1850nm signal light wavelengths (target band) point by point at similar positions of the same core of the bare fiber through the ultraviolet laser phase mask method; the transmittance of the cascaded high-reflection multi-core fiber Bragg grating to the pump light of 976nm (high-power pump laser) is 99.9%, and the reflectivity to the signal light wavelengths of 1030nm, 1535nm, and 1850nm (target band) is 99.9%, and the 3dB bandwidth of its reflection spectrum is 2nm; the reflectivity of the cascaded low-reflection multi-core fiber Bragg grating to the signal light wavelengths of 1030nm, 1535nm, and 1850nm (target band) is 15%, and the 3dB bandwidth of its reflection spectrum is 0.3nm.

[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 Yb3+ , co-doped with 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 in the shape of circles with different diameters. The distances between the centers of the two circles are 19μm, 19μm and 18μm respectively. The core diameters are 10μm, 9μm and 10μm respectively, and the numerical apertures are all 0.09 (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 with an inner cladding diameter of 250μm. Among them, the cladding light stripper (cladding light filter) is a passive multi-core double-clad optical fiber that strips off a coating layer of about 2cm in the middle. Along the direction from the input end to the output end, the bare fiber area is directly coated with two kinds of UV glue with low to high refractive index; the wavelength splitter is a 1×3 port type, which separates and outputs the 1030nm, 1535nm, and 1850nm signal light wavelengths (target bands) respectively.

[0086] The pump light (single-core beam) emitted by three multi-mode 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 grating (rear cavity mirror) through a 3×1 pump combiner. Under the continuous pumping of the multi-mode pump light source, the three rare-earth ion-doped cores (laser working medium) continuously pass through the three cores and are gradually absorbed by the different rare-earth luminescent ions doped in the three cores, forming a particle number inversion, and then the stimulated During the radiation process, stimulated radiation signal light of three bands is generated. Under the multiple feedback of the front cavity mirror and the rear cavity mirror of the three bands, the signal light in the three fiber cores oscillates back and forth and is amplified multiple times, so that the fiber laser simultaneously and efficiently lases and generates three bands of laser light of 1030nm, 1535nm, and 1850nm (the target laser beam corresponding to the target 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 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 shown in Figure 4.

[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 a wavelength of 808nm and a power of 60W; the N×1 pump combiner is a 7×1 port form, which uses 7 multimode optical fibers with a core diameter of 105μm as the pump input end and a passive single-core double-clad optical fiber with an inner cladding diameter of 300μm as the output end. Among them, the cascaded high-reflection multi-core fiber Bragg grating (the first multi-core fiber Bragg grating) and the cascaded low-reflection multi-core fiber Bragg grating (the second multi-core fiber Bragg grating) are two passive multi-core double-clad optical fibers stripped of their coatings, and then the fiber Bragg gratings with signal light wavelengths of 930nm, 1560nm, and 2100nm (target band) are written point by point at the same core of the bare fiber by femtosecond laser direct writing. The transmittance of the cascaded high-reflection multi-core fiber Bragg grating to the pump light of 808nm (high-power pump laser) is 99.9%, and the reflectivity to the signal light wavelengths of 930nm, 1560nm, and 2100nm (target band) is 99.9%, and the 3dB bandwidth of its reflection spectrum is 2nm; the reflectivity of the cascaded low-reflection multi-core fiber Bragg grating to the 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 with 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. 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 (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 with an inner cladding diameter of 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 refractive index from low to high. 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] The pump light (single-core beam) emitted by 7 multi-mode pump light sources with a wavelength of 808nm and a power of 60W is coupled into the multi-band laser resonant cavity from one end of the cascaded high-reflection multi-core fiber Bragg grating (rear cavity mirror) through a 7×1 pump combiner. Under the continuous pumping of the pump light source, the high-power pump laser of the three rare-earth ion-doped cores (laser working medium) continuously passes through the three cores and is gradually absorbed by the different rare-earth luminescent ions doped in the three cores to form a particle number inversion, and then a stimulated emission process occurs to generate stimulated emission signal light of three bands. Under the multiple feedback of the front and rear cavity mirrors of the three bands, the signal light in the three cores oscillates back and forth many times and is amplified many times, so that the laser simultaneously and efficiently emits and generates three-band lasers of 930nm, 1560nm, and 2100nm (the target laser beam corresponding to the target band); and then the wavelength demultiplexing function of the 1×3 splitter is used to enable the laser to achieve multi-port separation and stable output of the three bands. Finally, 930nm, 1560nm, and 2100nm can work simultaneously, with output powers of 150W, 80W, and 150W respectively, and beam quality factor M 2 The output spectrum of the fiber laser is shown in Figure 5.

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

[0092] In the description of this specification, the description with reference to the terms "some embodiments", "other embodiments", etc. 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 description of the above terms does not necessarily refer to the same embodiment or example.

[0093] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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 only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A multi-band high-power multi-core fiber laser, characterized in that: include: A pump excitation module, used to generate multiple multi-mode pump lasers; A pump beam combining module, connected to the pump excitation module, and used for combining multiple multi-mode pump light sources into a beam of high-power pump laser; A multi-band laser light source module, connected to the pump beam combining module, and used to generate target laser light beams corresponding to multiple target bands; A beam output module, 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 the target bands respectively; The multi-band laser light source module comprises a first multi-core fiber grating, a multi-core double-clad active fiber and a second multi-core fiber grating which are connected in sequence, the first multi-core fiber grating is connected to the pump beam combining module, the second multi-core fiber 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 located within the luminescent band of the rare earth ions.

2. The multi-band high-power multi-core fiber laser according to claim 1, characterized in that: A fiber Bragg grating corresponding to the target wavelength band is engraved on the bare core of the first multi-core fiber Bragg grating; The bare core of the second multi-core optical fiber Bragg grating is inscribed with an optical 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 smaller than the reflectivity and 3dB bandwidth of the reflection spectrum 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 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; The inner cladding shape of the multi-core double-cladding active optical fiber includes a rectangle, a hexagon, an octagon or a dodecagon.

6. 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 of the pump light sources is connected to the pump beam combining module, and the working band of the multi-mode pump laser is associated with the type of the rare earth ions.

7. The multi-band high-power multi-core fiber laser according to claim 1, characterized in that: The pump beam combining module comprises a pump beam combiner, the input end of the pump beam combiner is connected to the output end of the pump excitation module, and the output end of the pump beam combiner is connected to the first multi-core fiber 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.

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

9. The multi-band high-power multi-core fiber laser according to claim 8, characterized in that: 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 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, 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.

10. The multi-band high-power multi-core fiber laser according to claim 8, 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.

Images