High brightness and high power fiber laser

Abstract

A high-brightness, high-power fiber laser employs an oscillator structure comprising a pump module, a high-reflection fiber Bragg grating (FBG), a gain fiber, a low-reflection fiber Bragg grating (FBG), and a cladding light filter. The gain fiber is a rare-earth ion-doped ZBLAN fiber with an all-solid-state antiresonant structure using ZBLAN as the matrix material. The gain fiber comprises a core region, a cladding region, an antiresonant region, and a coating. The antiresonant region is composed of at least one capillary group, each of which includes multiple capillaries arranged in a ring around the core region. The matrix material within each capillary is the same as that in the cladding region and is ZBLAN. The ZBLAN matrix material in the core region is doped with dysprosium ions. The present invention utilizes a rare-earth-doped all-solid-state antiresonant fiber as the gain fiber, achieving high brightness, high power, and high efficiency output.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of optical fiber lasers, in particular to a high-brightness and high-power optical fiber laser. Background Art

[0002] Lasers with emission wavelengths between 380nm and 780nm (visible light band) have significant application prospects in medicine, astronomy, Bose-Einstein condensation, scientific research, laser displays, underwater communications, and other fields, and have garnered widespread attention in recent years. For example, blue-green lasers are ideal for underwater communications and detection, as they experience the lowest transmission loss in seawater in the blue-green wavelength band. Yellow lasers with a wavelength of 577±5nm are ideal for fundus laser photocoagulation. Laser guide star systems require narrow-linewidth yellow lasers with a wavelength of 589.1591nm.

[0003] Currently, visible light lasers include dye lasers, lasers based on nonlinear frequency conversion in crystals, rare-earth ion-doped solid-state lasers, and rare-earth ion-doped fiber lasers. A key approach to generating visible-light fiber lasers is to use rare-earth ion-doped fiber as a gain fiber to directly output visible light. This direct-output fiber laser offers high power, high beam quality, high efficiency, high robustness, high heat dissipation, and a simple, compact, and easily integrated system structure, making it a key development direction for visible-light lasers. Summary of the Invention

[0004] In view of the technical problems existing in the prior art, the present invention proposes a high-brightness and high-power fiber laser.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] This high-brightness, high-power fiber laser utilizes an oscillator structure, including a pump module, a high-reflection fiber Bragg grating (FBG), a gain fiber, a low-reflection fiber Bragg grating (FBG), and a cladding light filter. The antiresonance region is composed of at least one capillary group, each of which includes multiple capillaries arranged in a ring around the core region. The matrix material within each capillary is the same as that in the cladding region, namely ZBLAN. The ZBLAN matrix in the core region is doped with dysprosium ions. ZBLAN can be made from ZrF4, BaF2, LaF3, AIF3, or NaF.

[0007] Specifically, the pump module is used to output pump light. The pump module, high-reflection fiber Bragg grating (FBG), gain fiber, low-reflection fiber Bragg grating (FBG), and cladding light filter are sequentially connected. The high-reflection fiber Bragg grating and low-reflection fiber Bragg grating form a resonant cavity. The pump light is absorbed by the gain fiber. At a certain pump light power, signal light is emitted. The signal light oscillates and amplifies within the resonant cavity before being output through the low-reflection fiber Bragg grating and cladding light filter. The central wavelength of the pump source in the pump module must be within the absorption band of the doped ions.

[0008] Preferably, the optical fiber used to prepare the high-reflection fiber Bragg grating, the low-reflection fiber Bragg grating, and the cladding light filter is the same as the gain fiber.

[0009] Preferably, the reflection band center of the high-reflection fiber Bragg grating is at the signal light wavelength, the reflection bandwidth is 3nm, and the reflectivity is 99%; the reflection band center of the low-reflection fiber Bragg grating is at the signal light wavelength, the reflection bandwidth is 1nm, and the reflectivity is 4%~90%.

[0010] Preferably, the anti-resonance region is composed of a capillary group, which includes a plurality of capillaries, and the capillaries are circular nested tubes. The plurality of circular nested tubes surround the periphery of the core region, and the circular nested tubes include an outer tube and an inner tube arranged inside the outer tube and inscribed with the outer tube. There are gaps between adjacent circular nested tubes and the gaps are equal.

[0011] Preferably, the outer diameter of the circular nested tube in the gain optical fiber is d1, the inner diameter is d2, and the wall thickness of the outer and inner tubes is the same. t By optimizing d1 and d2, the value of the higher-order mode suppression ratio (HOMER) at the signal light wavelength is made greater than 100, achieving single-mode transmission and improving the output beam quality.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] The high-brightness, high-power fiber laser proposed in the present invention adopts an all-fiber laser and adopts a rare-earth-doped all-solid-state antiresonant fiber as a gain fiber, which can achieve high-brightness, high-power, and high-efficiency visible light output. It has the advantages of simple and compact structure, good heat dissipation effect, high robustness, and high beam quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0015] Figure 1 Schematic diagram of the structure of a high-brightness and high-power fiber laser in one embodiment;

[0016] Figure 2 Schematic diagram of the structure of the gain optical fiber used in one embodiment;

[0017] Figure 3 In one embodiment, d2 / d1=0.5, 575nm fundamental mode (LP 01 ) The limiting loss curve as a function of d1 / D;

[0018] Figure 4 In one embodiment, d1 / D=0.71, the fundamental mode (LP 01 ), higher order modes (LP 11 ) The limiting loss and higher-order mode suppression ratio (HOMER) change with d2 / d1;

[0019] Numbers in the figure:

[0020] 1. Pump module; 2. High-reflection fiber Bragg grating; 3. Gain fiber; 4. Low-reflection fiber Bragg grating; 5. Cladding light filter;

[0021] 10. Fiber core region; 20. Cladding region; 30. Antiresonance region; 40. Coating layer; 301. Outer tube; 302. Inner tube. DETAILED DESCRIPTION

[0022] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0023] Reference Figure 1 , a high-brightness, high-power fiber laser in one embodiment, employs an oscillator structure comprising a pump module 1, a high-reflection fiber Bragg grating 2, a gain fiber 3, a low-reflection fiber Bragg grating 4, and a cladding light filter 5. The pump module 1 is used to output pump light. These are sequentially connected, forming a resonant cavity between the high-reflection fiber Bragg grating 2 and the low-reflection fiber Bragg grating 4. Pump light is absorbed by the gain fiber 3. At a certain pump light power, signal light is emitted. The signal light oscillates and amplifies within the resonant cavity before being output through the low-reflection fiber Bragg grating 4 and the cladding light filter 5. The central wavelength of the pump source in the pump module must be within the absorption band of the doped ions.

[0024] The reflection band center of the high-reflection fiber Bragg grating 2 is at the signal light wavelength, the reflection bandwidth is 3nm, and the reflectivity is 99%. The reflection band center of the low-reflection fiber Bragg grating 4 is at the signal light wavelength, the reflection bandwidth is 1nm, and the reflectivity is 4%~90%.

[0025] Reference Figure 2 , is a schematic diagram of the structure of a gain fiber used in one embodiment. The gain fiber 3 is a rare earth ion-doped ZBLAN fiber with an all-solid-state antiresonant structure using ZBLAN as the matrix material. The gain fiber includes a core region 10, a cladding region 20, an antiresonant region 30, and a coating layer 40. Only the matrix material in the core region 10 is doped with dysprosium ions. The design of the tube structure in the antiresonant region 30 is not limited. Those skilled in the art can design a suitable antiresonant structure based on actual needs and process difficulty. The antiresonant region 30 is composed of at least one capillary group, each capillary group including multiple capillaries. The capillaries in each capillary group are arranged in a ring around the core region with the core region as the center. The matrix material in each capillary is the same as the matrix material in the cladding region and is ZBLAN. The matrix material ZBLAN in the core region is doped with dysprosium ions. ZBLAN is a matrix material made of ZrF4, BaF2, LaF3, AIF3, and NaF. The material composition ratio is not limited. Those skilled in the art can select an appropriate ratio based on experience or existing technology, or directly use commercially available ZBLAN materials. The capillaries in the same capillary set have identical structural and dimensional parameters. The structural and dimensional parameters of the capillaries in different capillary sets can be identical or different. The cross-sectional shape of the capillaries is not limited; however, a circular shape is typically used for ease of drawing.

[0026] Figure 2 In the illustrated embodiment, the antiresonance region 30 is composed of a capillary group, which includes a plurality of capillaries. The capillaries are circular nested tubes. The plurality of circular nested tubes surround the periphery of the core region 10. The circular nested tubes include an outer tube 301 and an inner tube 302 arranged inside the outer tube 301 and inscribed with the outer tube. There are gaps between adjacent circular nested tubes and the gaps are equal.

[0027] The outer diameter of the circular nested tube in the gain optical fiber 3 is d1, the inner diameter is d2, and the wall thickness of the outer tube 301 and the inner tube 302 are the same. t By optimizing d1 and d2, the high-order mode suppression ratio at the signal wavelength is made greater than 100, achieving single-mode transmission and improving the output beam quality. Specifically, COMSOL software is used to optimize the gain fiber parameters. The process of optimizing d1 and d2 includes:

[0028] Fix d2 / d1 as a set value (those skilled in the art can select an appropriate empirical value as the set value of d2 / d1 based on experience), optimize d1 / D, where D is known, obtain a curve of the fundamental mode limiting loss of the signal light wavelength versus d1 / D, and take the d1 / D value corresponding to the minimum fundamental mode limiting loss of the signal light wavelength as the optimal value of d1 / D, thereby determining the optimal value of d1;

[0029] Fix d1 / D as the obtained optimal value of d1 / D, optimize d2 / d1, and obtain the curves of the fundamental mode limiting loss, high-order mode limiting loss and high-order mode suppression ratio of the signal light wavelength as a function of d2 / d1. Select the d2 / d1 value corresponding to the high-order mode suppression ratio value greater than 100 and the minimum fundamental mode limiting loss as the optimal value of d2 / d1, and then determine the optimal value of d2.

[0030] In a specific embodiment, based on Figure 1 The structure shown in FIG1 is a high brightness and high power 575nm fiber laser, which is used to generate and output high brightness and high power 575nm fiber laser. The pump source of the pump module 1 adopts a semiconductor laser with a central wavelength of 450nm. The structure of the gain fiber used is as shown in FIG1. Figure 2 As shown, no further details are given here. The optical fiber used to prepare the high-reflection fiber Bragg grating 2, the low-reflection fiber Bragg grating 4, and the cladding light filter 5 is the same as the gain fiber 3. The reflection band center of the high-reflection fiber Bragg grating 2 is 575nm, the reflection bandwidth is 3nm, and the reflectivity is 99%. The reflection band center of the low-reflection fiber Bragg grating 4 is 575nm, the reflection bandwidth is 1nm, and the reflectivity varies from 4% to 90%. The outer tube 301 of the circular nested tube in the gain fiber 3 has a diameter of d1, and the inner tube 302 has a diameter of d2. The wall thickness of the outer tube 301 and the inner tube 302 are the same. t By optimizing d1 and d2, the value of the higher-order mode suppression ratio (HOMER) at 575nm is greater than 100, achieving single-mode transmission and improving the output beam quality.

[0031] The diameter of the core region of the gain fiber 3 is D = 20 μm; the diameter of the outer tube 301 of the circular nested tube is d1 and the diameter of the inner tube 302 is d2, and the wall thickness of the outer tube 301 and the inner tube 302 are the same. t According to the anti-resonance theory ( n 2 and n 1 is the refractive index of the antiresonance region and the core region, m is a positive integer), The resonant wavelength cannot be transmitted in the fiber core. For the visible light band, the diameter of the core region D = 20μm, which belongs to a large mode field and can achieve high power transmission. Combined with the flexibility of the high-order mode suppression ratio (HOMER) control of antiresonant fiber, it is possible to design a single-mode transmission fiber, thereby achieving high brightness transmission. The maximum core diameter of the currently commonly used step-index fiber is 16μm, and the output laser beam quality is very poor. 2 ~6.08.

[0032] The optical fiber of the present invention utilizes a ZBLAN matrix with relatively low phonon energy because a matrix with high phonon energy enhances the non-radiative relaxation process during ion transitions, which is detrimental to lasing. Furthermore, ZBLAN-based optical fibers have a relatively low refractive index and low dispersion in the visible light band, allowing for a wide transmission bandwidth while maintaining an appropriate wall thickness and facilitating fiber drawing. Excessively thick walls affect transmission losses, further impacting the output laser power level and fiber laser efficiency.

[0033] Combined with the refractive index of the optical fiber matrix, ZBLAN (ZrF4-BaF2-LaF3-AIF3-NaF) is used as the matrix material, and the wall thickness of the outer tube 301 and the inner tube 302 is t The preferred value is 1.5μm. By optimizing d1 and d2, the value of the high-order mode suppression ratio (HOMER) at 575nm is greater than 100. A value of HOMER greater than 100 can be considered as single-mode transmission with high beam quality. This embodiment proposes a double-clad, all-solid-state antiresonant optical fiber with a large mode field and high suppression ratio suitable for the visible light band to achieve the purpose of high-power, high-brightness laser transmission. COMSOL software is used to optimize the design of optical fiber parameters. First, the optical fiber matrix material and the shape structure of the antiresonance region are determined, and combined with actual applications, the diameter of the core region that meets the requirements of high-power visible light transmission is determined (the diameter of the core region in this embodiment is D=20μm); secondly, because the pump light needs to be precisely located at the resonant wavelength, the wall thickness of the outer tube and the inner tube of the antiresonance region is determined based on the antiresonance theory in combination with the actual drawing difficulty and the influence of the wall thickness on the optical fiber loss. t The preferred value (this embodiment t The preferred value is 1.5μm) and this parameter is entered. Based on this, a signal laser wavelength of 575nm is input. Next, the outer and inner diameters of the circular nested tubes, d1 and d2, are optimized to achieve a higher-order mode suppression ratio (HOMER) greater than 100 at the signal laser wavelength, supporting high-brightness transmission of 575nm laser light. COMSOL software is used to optimize the gain fiber parameters. The optimization process for d1 and d2 includes the following steps:

[0034] Fixed d2 / d1=0.5, optimized d1 / D, where D is known, D=20μm, and obtained the 575nm wavelength fundamental mode (LP 01 ) The curve of limiting loss versus d1 / D is as follows Figure 3 As shown, the fundamental mode (LP) at 575 nm wavelength is taken 01 ) The d1 / D value corresponding to the minimum loss value is the preferred value of d1 / D (0.71 in this embodiment), and then the preferred value of d1 is determined (14.2μm in this embodiment). Figure 3 As can be seen from the figure, the value of d1 / D is related to the fundamental mode (LP 01 ) The limiting loss value does not change regularly, and the optimal value can only be obtained through optimized design.

[0035] Fixed d1 / D to the obtained optimal value of d1 / D (0.71 in this embodiment), optimized d2 / d1, and obtained the 575nm wavelength fundamental mode (LP 01 ) limit loss, high order mode (LP 11 ) The limiting loss and the high-order mode suppression ratio (HOMER) change with d2 / d1, as shown in the figure. Figure 4 As shown, the fundamental mode (LP 01 ) When the limiting loss is small and the high-order mode suppression ratio (HOMER) value is greater than 100, the corresponding d2 / d1 value is the preferred value of d2 / d1 (0.61 in this embodiment), and then the preferred value of d2 is determined (8.662μm in this embodiment).

[0036] Matters not covered by the present invention are known technologies.

[0037] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above 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.

[0038] 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 invention. 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 such modifications and improvements are intended to 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.

[0039] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can be modified and varied in various ways. For example, gain fibers with other structural parameters can be designed, doping ions can be changed, and the pump light wavelength can be changed to achieve laser output of other signal wavelengths. Similarly, based on Figure 1The optical path structure shown in FIG. 1 is a high-brightness, high-power fiber laser according to an embodiment of the present invention, which is used to generate and output high-brightness, high-power 2μm and 2.3μm fiber laser outputs. The pump source of the pump module 1 adopts a semiconductor laser with a central wavelength of 793nm. The structure of the gain fiber used is as follows: Figure 2 As shown, and not detailed here, the matrix material ZBLAN in the core region of the gain fiber 3 is doped with thulium ions. The optical fibers used to prepare the high-reflection fiber Bragg grating 2, low-reflection fiber Bragg grating 4, and cladding light filter 5 are the same as those used for the gain fiber 3. The optimization design method for the outer and inner tubes in the antiresonance region of the gain fiber 3 is the same as that in the above-mentioned embodiment and is not detailed here.

[0040] based on Figure 1 The optical path structure shown in FIG. 1 is a high-brightness high-power fiber laser, which is used to generate and output high-brightness high-power 1.9 μm fiber laser output. The pump source of the pump module 1 adopts a laser with a central wavelength of 1064 nm. The structure of the gain fiber used is as shown in FIG. Figure 2 As shown, and not detailed here, the matrix material ZBLAN in the core region of the gain fiber 3 is doped with thulium ions. The optical fibers used to prepare the high-reflection fiber Bragg grating 2, low-reflection fiber Bragg grating 4, and cladding light filter 5 are the same as those used for the gain fiber 3. The optimization design method for the outer and inner tubes in the antiresonance region of the gain fiber 3 is the same as that in the above-mentioned embodiment and is not detailed here.

[0041] based on Figure 1 The optical path structure shown in FIG. 1 is a high-brightness, high-power fiber laser according to an embodiment of the present invention, which is used to generate and output high-brightness, high-power 3.24 μm fiber laser output. The pump source of the pump module 1 adopts a laser with a central wavelength of 980 nm. The structure of the gain fiber used is as follows: Figure 2 As shown, the matrix material ZBLAN in the core region of the gain fiber 3 is doped with dysprosium ions. The high-reflection fiber Bragg grating 2, low-reflection fiber Bragg grating 4, and cladding light filter 5 are made from the same optical fibers as those used for the gain fiber 3. The optimization design method for the outer and inner tubes in the antiresonance region of the gain fiber 3 is the same as that in the above-described embodiment and is not repeated here.

[0042] based on Figure 1 The optical path structure shown in FIG. 1 is a high-brightness, high-power fiber laser according to an embodiment of the present invention, which is used to generate and output high-brightness, high-power 2.9 μm fiber laser output. The pump source of the pump module 1 adopts a laser with a central wavelength of 1.1 μm or 1.3 μm. The structure of the gain fiber used is as follows: Figure 2As shown, the matrix material ZBLAN in the core region of the gain fiber 3 is doped with dysprosium ions. The high-reflection fiber Bragg grating 2, low-reflection fiber Bragg grating 4, and cladding light filter 5 are made from the same optical fibers as those used for the gain fiber 3. The optimization design method for the outer and inner tubes in the antiresonance region of the gain fiber 3 is the same as that in the above-described embodiment and is not repeated here.

[0043] Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. High brightness and high power fiber laser, using an oscillator structure, including a pump module, a high reflection fiber Bragg grating, a gain fiber, a low reflection fiber Bragg grating and a cladding light filter, characterized by: The gain fiber is a rare earth ion doped ZBLAN fiber with an all-solid-state antiresonant structure using ZBLAN as a matrix material. The gain fiber includes a core region, a cladding region, an antiresonant region, and a coating layer. The antiresonant region is composed of at least one capillary group, each capillary group includes a plurality of capillaries, and the capillaries in each capillary group are arranged in a ring around the core region with the core region as the center. The matrix material in each capillary is the same as the matrix material in the cladding region and is all ZBLAN. The matrix material ZBLAN in the core region is doped with dysprosium ions. The antiresonant region is composed of a capillary group, the capillary group includes a plurality of capillaries, and the capillaries are circular nested tubes. The plurality of circular nested tubes surround the periphery of the core region, and a gap is provided between each circular nested tube and the coating layer. The circular nested tubes include an outer tube and an inner tube arranged inside the outer tube and inscribed with the outer tube. A gap is provided between adjacent circular nested tubes, and the gaps are equal. The outer tube diameter of the circular nested tubes in the gain fiber is d1, the inner tube diameter is d2, and the wall thickness of the outer tube and the inner tube is the same. t By optimizing d1 and d2, the high-order mode suppression ratio at the signal wavelength is made greater than 100, single-mode transmission is achieved, and the output beam quality is improved. COMSOL software is used to optimize the gain fiber parameters. The process of optimizing d1 and d2 includes: Fix d2 / d1 as a set value and optimize d1 / D, where the diameter D of the fiber core region is known. Obtain a curve of the fundamental mode limiting loss of the signal light wavelength versus d1 / D. Take the d1 / D value corresponding to the minimum fundamental mode limiting loss of the signal light wavelength as the optimal value of d1 / D, and then determine the optimal value of d1; Fix d1 / D as the obtained optimal value of d1 / D, optimize d2 / d1, and obtain the curves of the fundamental mode limiting loss, high-order mode limiting loss and high-order mode suppression ratio of the signal light wavelength as a function of d2 / d1. Select the d2 / d1 value corresponding to the high-order mode suppression ratio value greater than 100 and the minimum fundamental mode limiting loss as the optimal value of d2 / d1, and then determine the optimal value of d2.

2. The high-brightness, high-power fiber laser according to claim 1, characterized in that: The pump module is used to output pump light. The pump module, high-reflection fiber Bragg grating, gain fiber, low-reflection fiber Bragg grating and cladding light filter are connected in sequence. The resonant cavity formed between the high-reflection fiber Bragg grating and the low-reflection fiber Bragg grating is used to absorb the pump light. Under a certain pump light power, signal light is emitted. The signal light oscillates and amplifies in the resonant cavity and is output through the low-reflection fiber Bragg grating and cladding light filter.

3. The high-brightness, high-power fiber laser according to claim 2, characterized in that: The central wavelength of the pump source of the pump module must be within the absorption band of the doped ions.

4. The high-brightness, high-power fiber laser according to claim 1, 2 or 3, characterized in that: The optical fiber used to prepare the high-reflection fiber Bragg grating, the low-reflection fiber Bragg grating and the cladding light filter is the same as the gain fiber.

5. The high-brightness, high-power fiber laser according to claim 2, characterized in that: The reflection band center of the high-reflection fiber Bragg grating is at the signal light wavelength, the reflection bandwidth is 3nm, and the reflectivity is 99%. The reflection band center of the low-reflection fiber Bragg grating is at the signal light wavelength, the reflection bandwidth is 1nm, and the reflectivity is 4%~90%.

6. The high-brightness, high-power fiber laser according to claim 1, 2, 3, or 5, characterized in that: The pump module is a semiconductor laser with a pump source center wavelength at 450nm, and the high-brightness and high-power fiber laser is used to generate and output high-brightness and high-power 575nm fiber laser.

7. The high-brightness, high-power fiber laser according to claim 6, characterized in that: The wall thickness of the outer tube and the inner tube in the anti-resonance region of the gain optical fiber t The diameter of the core region is D=1.5 μm, and the preferred values of d1 and d2 are 14.2 μm and 8.662 μm respectively.

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