Low-temperature operating fiber laser

Abstract

The invention discloses a fiber laser operating at low temperature, which comprises a pumping module and a gain fiber, each pumping source in the pumping module is a non-wavelength-locked semiconductor laser, the central wavelength of each pumping source at normal temperature is located in the valley bottom area at the right side of the absorption peak of the gain fiber, and when the temperature is reduced to zero or below zero, the gain fiber is switched off. The central wavelength of each pumping source moves towards a short wave, so that when the temperature is reduced to 0 DEG C or below, the result of the central wavelength drift of the pumping sources is that the pumping absorption of the gain fiber is enhanced. Furthermore, the gain optical fiber is coated with a temperature-insensitive low-refractive-index material layer outside the inner cladding for transmitting the pump light, and due to the design, the transmission loss of the pump light cannot be influenced by temperature change. The optical fiber laser can efficiently generate laser in a low-temperature environment through targeted design of devices, and can be applied to a special temperature environment.

Description

Technical Field

[0001] The invention mainly relates to the technical field of high-power optical fiber lasers, in particular to an optical fiber laser operating at low temperature. Background Art

[0002] Fiber lasers have the advantages of compact structure, high efficiency, and good beam quality. They are widely used in industrial processing, medical treatment, sensing, scientific research, etc. The operating temperature of traditional fiber lasers is usually near room temperature and cannot adapt to a wider temperature range, especially low temperature environments. With the expansion of fiber laser applications, the application environment of lasers has become more and more complex, and laser solutions that can adapt to various temperature environments are urgently needed. However, at present, almost all high-power fiber lasers cannot directly adapt to low-temperature environments. There are many mechanism problems that need to be solved here, such as temperature causing the pump wavelength to move, thereby greatly changing the absorption characteristics; temperature causing changes in the fiber coating material, thereby increasing the loss of the cladding transmission light; temperature causing the loss of highly doped cores to increase, etc. At present, there are literature reports that the efficiency of fiber lasers decreases in low-temperature environments, which is not conducive to the low-temperature application and system safety of high-power fiber lasers. Summary of the invention

[0003] In view of the problem that the current high-power fiber laser cannot be directly applied to low-temperature environments, the present invention proposes a low-temperature operating fiber laser.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is as follows: On the one hand, the present invention provides a low-temperature-operating fiber laser, a pump module and a gain fiber, wherein each pump source in the pump module is a non-wavelength-locked semiconductor laser, and the central wavelength of each pump source at room temperature is located in the valley area on the right side of the gain fiber absorption peak. When the temperature drops to zero degrees or below zero degrees, the central wavelength of each pump source moves to a short wave, thereby ensuring that when the temperature drops to zero degrees or below zero degrees, the central wavelength of the pump source drifts, resulting in enhanced pump absorption of the gain fiber.

[0005] Furthermore, the gain optical fiber at least includes a core, a first inner cladding, a second inner cladding and an outer cladding, wherein the core is an active region doped with ytterbium ions, the first inner cladding is a quartz material having a refractive index lower than that of the core, and in order to facilitate cladding light absorption, the cross-sectional shape may be an octagon, a D-shape, etc.; the second inner cladding is adjacent to the first inner cladding and is a temperature-sensitive low-refractive index material layer, the refractive index of the material being slightly lower than that of the first inner cladding, such as a fluorine-doped quartz material, etc.; the outer cladding is a protective layer of the optical fiber, and may be a low-refractive index resin material or a metal coating.

[0006] Furthermore, the core of the gain optical fiber is doped with phosphorus and / or aluminum to make the peaks and valleys of its absorption spectrum flatter, wherein if phosphorus and aluminum are doped at the same time, the ratio of the doped phosphorus element to the doped aluminum element is within 0-1.2.

[0007] Furthermore, the central wavelength of each pump source in the pump module at room temperature is between 930nm and 950nm or between 1000nm and 1020nm.

[0008] Furthermore, the low-temperature-operating fiber laser comprises a pump coupler, and each pump source couples the pump light output by the pump source into the cladding of the gain fiber through the pump coupler.

[0009] Furthermore, one end of the gain optical fiber is connected to a high reflectivity grating, and the other end of the gain optical fiber is connected to a low reflectivity grating, and the high reflectivity grating and the low reflectivity grating constitute two end faces of the resonant cavity.

[0010] Furthermore, the central wavelengths of the high-reflectivity grating and the low-reflectivity grating are consistent and are used to select lasers of target wavelengths for amplification. The reflectivity of the high-reflectivity grating is ≥90%, and the reflectivity of the low-reflectivity grating is ≤20%.

[0011] Furthermore, the cladding pump absorption coefficient of the gain optical fiber at the peak wavelength is 0.2 dB / m to 2.5 dB / m. If the absorption coefficient is too large, the low temperature loss of the optical fiber will also increase.

[0012] Furthermore, the length of the gain optical fiber matches the central wavelength of the pump source in the pump module at room temperature, so that the total absorption coefficient reaches 10 dB to 30 dB.

[0013] Furthermore, the low-temperature operating fiber laser includes a cladding light filter and a fiber output end cap, which are used to filter the cladding light from the optical fiber, and output the light transmitted through the fiber core as the output laser of the fiber laser to the fiber output end cap, and the fiber output end cap outputs the output laser into space.

[0014] Compared with the prior art, the technical effects of the present invention are: Each pump source in the pump module of the present invention is a non-wavelength locked semiconductor laser, and the central wavelength of each pump source at room temperature is located in the valley area on the right side of the gain fiber absorption peak, and when the temperature drops to zero degrees or below zero degrees, the central wavelength of each pump source moves to the short wave (that is, moves to the two absorption peaks of 976nm or 915nm), thereby ensuring that when the temperature drops to zero degrees or below zero degrees, the central wavelength of the pump source drifts, resulting in enhanced pump absorption of the gain fiber.

[0015] Furthermore, the gain fiber is a doped fiber with low temperature sensitivity and ytterbium ions doped in the core. For the gain fiber, the use of temperature-sensitive materials such as acrylate as the coating layer in contact with the first inner cladding in the traditional double cladding structure is avoided. The gain fiber in the present invention preferably uses a low-refractive-index material such as fluorine-doped quartz as the second inner cladding, so that the light transmission characteristics of the first inner cladding will not change significantly at low temperatures, reducing the pump light transmission loss of the optical fiber at low temperatures, thereby ensuring that the cladding transmission efficiency will not decrease with temperature.

[0016] The present invention enables the efficiency of the optical fiber laser to remain stable in a low-temperature environment, making it easier to carry out subsequent applications and scientific research. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative work.

[0018] Figure 1 This is a schematic diagram of the lateral structure of a gain optical fiber suitable for low-temperature operation; Figure 2 It is a schematic diagram of the structure of a low-temperature-operated fiber laser with a forward pumping structure; Figure 3 It is a schematic diagram of the structure of a low-temperature-operated fiber laser with a backward pumping structure; Figure 4 It is a schematic diagram of the structure of a low-temperature-operated fiber laser with a bidirectional pumping structure; Figure 5 It is the cladding absorption spectrum of the conventional double-clad ytterbium-doped fiber; Figure 6 The absorption spectrum of the ytterbium-doped optical fiber cladding of the temperature-insensitive low-refractive index material layer outside the first inner cladding proposed by the present invention; Markings in the figure: 11. Fiber core, 12. First inner cladding, 13. Second inner cladding, 14. Outer cladding, 1-1. Front pump module, 1-2. Rear pump module, 2-1. Front pump coupler, 2-2. Rear pump coupler, 3. High reflectivity grating, 4. Gain fiber, 5. Low reflectivity grating, 6. Cladding light filter, 7. Fiber output end cap. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present application belongs. 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 "forward", "backward", 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 one way from another.

[0021] The main difference between the present invention and the existing conventional high-power fiber laser is that the present invention can achieve the characteristic of stable efficiency under low temperature conditions, which is an effect that conventional fiber lasers cannot directly achieve. The present invention is further described below with reference to the figures.

[0022] The present invention provides a low-temperature-operated optical fiber laser, a pump module and a gain optical fiber. Each pump source in the pump module is a non-wavelength-locked semiconductor laser. The central wavelength of each pump source at room temperature is located in the valley bottom area on the right side of the gain optical fiber absorption peak. When the temperature drops to zero degrees or below zero degrees, the central wavelength of each pump source moves to a short wave, thereby ensuring that when the temperature drops to zero degrees or below zero degrees, the central wavelength of the pump source drifts, so that the pump absorption of the gain optical fiber is enhanced.

[0023] Because the refractive index of traditional optical fiber coating increases at low temperatures, the transmission loss of pump light increases. Figure 1 , Figure 1 The schematic diagram of the transverse structure of a gain optical fiber suitable for low temperature operation includes a core 11, a first inner cladding 12, a second inner cladding 13, and an outer cladding 14. The core 11 is doped with ytterbium ions, and the ytterbium ion concentration is less than 10 27 m -3 There is a protective layer outside the first inner cladding 12 for transmitting pump light, namely, the second inner cladding 13. The refractive index of the second inner cladding 13 is slightly lower than that of the first inner cladding 12, and it can be a fluorine-doped quartz glass material. The outer cladding 14 is wrapped with the second outer cladding for protection. The coating material can be a metal or a traditional resin material. The gain optical fiber of the present invention is coated with a temperature-insensitive low-refractive index material layer outside the inner cladding for transmitting pump light. This design ensures that the transmission loss of the pump light will not be affected by temperature changes.

[0024] Specifically, the low-temperature-operated fiber laser includes a pump module, a pump coupler, a high-reflectivity grating, a gain fiber, a low-reflectivity grating, a pump filter and a fiber output end cap. The pump module is connected to the pump coupler, and the high-reflectivity grating, the gain fiber, the low-reflectivity grating, the pump filter and the fiber output end cap are connected in sequence. According to the position of the pump coupler, it is divided into a forward pumping mode, a subsequent pumping mode and a bidirectional pumping mode. When the pump coupler is at the high-reflectivity grating end, it is a forward pumping mode; when the pump coupler is at the low-reflectivity grating end, it is a backward pumping mode; when there is a pump coupler at each end of the high-reflectivity grating and the low-reflectivity grating, it is a bidirectional pumping mode.

[0025] Figure 2 It is a schematic diagram of the structure of a low-temperature fiber laser with a forward pumping structure, including a front pump module 1-1, a front pump coupler 2-1, a high reflectivity grating 3, a gain fiber 4, a low reflectivity grating 5, a cladding light filter 6, and a fiber output end cap 7. The front pump coupler 2-1, the high reflectivity grating 3, the gain fiber 4, the low reflectivity grating 5, the cladding light filter 6, and the fiber output end cap 7 are sequentially connected by fiber fusion. One end of the gain fiber 4 is connected to the high reflectivity grating 3, and the other end of the gain fiber 4 is connected to the low reflectivity grating 5. The high reflectivity grating 3 and the low reflectivity grating 5 constitute the two end faces of the resonant cavity. The core and first cladding diameter and numerical aperture of the input fiber of the right fiber device in the adjacent fiber devices are not less than the core and first cladding diameter and numerical aperture of the output fiber of the left fiber device. In addition, the front pump module 1-1 is connected to the front pump coupler 2-1 by fiber fusion splicing, ensuring that the core and cladding diameters and numerical apertures of the output fiber of the front pump module 1-1 are not less than the core and cladding diameters and numerical apertures of the pump arm fiber of the front pump coupler 2-1. Each pump source in the front pump module 1-1 couples the pump light output by the pump source to the cladding of the gain fiber 4 through the front pump coupler 2-1. Each pump source in the front pump module 1-1 is a non-wavelength locked semiconductor laser, and the central wavelength of each pump source at room temperature is located in the valley area on the right side of the gain fiber absorption peak. When the temperature drops to zero or below zero, the central wavelength of each pump source moves to the short wave, thereby ensuring that when the temperature drops to zero or below zero, the central wavelength of the pump source drifts, resulting in enhanced pump absorption of the gain fiber. The cladding light filter 6 is used to filter out the cladding light from the optical fiber, and output the light transmitted through the fiber core as the output laser of the optical fiber laser to the optical fiber output end cap 7, and the optical fiber output end cap 7 outputs the output laser to space.

[0026] Figure 3It is a structural schematic diagram of a low-temperature fiber laser with a backward pumping structure, including a high reflectivity grating 3, a gain fiber 4, a low reflectivity grating 5, a back-pumping coupler 2-2, a back-pumping module 1-2, a cladding light filter 6, and a fiber output end cap 7. The fiber components, such as the high reflectivity grating 3, the gain fiber 4, the low reflectivity grating 5, the back-pumping coupler 2-2, the cladding light filter 6, and the fiber output end cap 7, are sequentially connected by fiber fusion. One end of the gain fiber 4 is connected to the high reflectivity grating 3, and the other end of the gain fiber 4 is connected to the low reflectivity grating 5. The high reflectivity grating 3 and the low reflectivity grating 5 constitute the two end faces of the resonant cavity. The core and first cladding diameter and numerical aperture of the input fiber of the right fiber component among the adjacent fiber components are not less than the core and first cladding diameter and numerical aperture of the output fiber of the left fiber component. In addition, the rear pump module 1-2 is connected to the rear pump coupler 2-2 by fiber fusion splicing, ensuring that the core and cladding diameters and numerical apertures of the output optical fiber of the rear pump module 1-2 are not less than the core and cladding diameters and numerical apertures of the pump arm optical fiber of the rear pump coupler 2-2. Each pump source in the rear pump module 1-2 couples the pump light output by the pump source to the cladding of the gain optical fiber 4 through the rear pump coupler 2-2. Each pump source in the rear pump module 1-2 is a non-wavelength locked semiconductor laser, and the central wavelength of each pump source at room temperature is located in the valley area on the right side of the gain optical fiber absorption peak. When the temperature drops to zero or below zero, the central wavelength of each pump source moves to the short wave, thereby ensuring that when the temperature drops to zero or below zero, the central wavelength of the pump source drifts, resulting in enhanced pump absorption of the gain optical fiber. The cladding light filter 6 is used to filter out the cladding light from the optical fiber, and output the light transmitted through the fiber core as the output laser of the optical fiber laser to the optical fiber output end cap 7, and the optical fiber output end cap 7 outputs the output laser to space.

[0027] Figure 4 It is a schematic diagram of the structure of a low-temperature fiber laser with a bidirectional pumping structure, including a front pump module 1-1, a rear pump module 1-2, a front pump coupler 2-1, a rear pump coupler 2-2, a high reflectivity grating 3, a gain fiber 4, a low reflectivity grating 5, a cladding light filter 6, and a fiber output end cap 7. Among them, the front pump coupler 2-1, the high reflectivity grating 3, the gain fiber 4, the low reflectivity grating 5, the rear pump coupler 2-2, the cladding light filter 6 and the fiber output end cap 7 are sequentially connected by fiber fusion. One end of the gain fiber 4 is connected to the high reflectivity grating 3, and the other end of the gain fiber 4 is connected to the low reflectivity grating 5. The high reflectivity grating 3 and the low reflectivity grating 5 constitute the two end faces of the resonant cavity. The core and first cladding diameter and numerical aperture of the input fiber of the right fiber device in the adjacent fiber devices are not less than the core and first cladding diameter and numerical aperture of the output fiber of the left fiber device.

[0028] In addition, the front pump module 1-1 is connected to the front pump coupler 2-1 by fiber fusion splicing, ensuring that the core and cladding diameters and numerical apertures of the output fiber of the front pump module 1-1 are not less than the core and cladding diameters and numerical apertures of the pump arm fiber of the front pump coupler 2-1. The rear pump module 1-2 is connected to the rear pump coupler 2-2 by fiber fusion splicing, ensuring that the core and cladding diameters and numerical apertures of the output fiber of the rear pump module 1-2 are not less than the core and cladding diameters and numerical apertures of the pump arm fiber of the rear pump coupler 2-2. Each pump source in the front pump module 1-1 couples the pump light output by the pump source into the cladding of the gain fiber 4 through the front pump coupler 2-1. Each pump source in the rear pump module 1-2 couples the pump light output by the pump source into the cladding of the gain fiber 4 through the rear pump coupler 2-2. Each pump source in the front pump module 1-1 and the rear pump module 1-2 is a non-wavelength locked semiconductor laser. The central wavelength of each pump source at room temperature is located in the valley area on the right side of the gain fiber absorption peak. When the temperature drops to zero or below zero, the central wavelength of each pump source moves to the short wave, thereby ensuring that when the temperature drops to zero or below zero, the central wavelength of the pump source drifts, resulting in enhanced pump absorption of the gain fiber. The cladding light filter 6 is used to filter the cladding light from the optical fiber, and guide the light transmitted through the core as the output laser of the optical fiber laser to the optical fiber output end cap 7, and the optical fiber output end cap 7 outputs the output laser to space.

[0029] Figure 2 , Figure 3 as well as Figure 4 In the embodiment shown in , each pump source in the pump module is a non-wavelength locked semiconductor laser, and the central wavelength of each pump source at room temperature is located in the valley area on the right side of the gain fiber absorption peak. When the temperature drops to zero degrees or below zero degrees, the central wavelength of each pump source moves to the short wave, thereby ensuring that when the temperature drops to zero degrees or below zero degrees, the central wavelength of the pump source drifts, resulting in enhanced pump absorption of the gain fiber. Further, the gain fiber is a doped fiber with low temperature sensitivity and ytterbium ions doped in the core. The gain fiber is preferably a three-clad doped fiber or a doped fiber with a metal coating layer, so that the cladding loss of the gain fiber under low temperature conditions will not increase significantly, thereby ensuring that the cladding transmission efficiency will not decrease with temperature. In summary, the low absorption pump wavelength at room temperature and the temperature-insensitive gain fiber are used to overcome the changes in material properties caused by low temperature, and the temperature environment adaptability of the fiber laser is improved.

[0030] Further, Figure 2 , Figure 3 as well as Figure 4 In the embodiment shown in, the following preferred settings are also included: The central wavelength of the pump source in the pump module at room temperature is between 930nm and 950nm or between 1000nm and 1020nm.

[0031] The front pump coupler 2-1 and the rear pump coupler 2-2 are used to inject pump light into the cladding of the gain fiber. One end of the pump coupler includes a plurality of pump arms and a signal arm, and the other end includes an output fiber.

[0032] The central wavelengths of the high reflectivity grating 3 and the low reflectivity grating 5 are consistent and are used to select lasers of target wavelengths for amplification. The reflectivity of the high reflectivity grating 3 is ≥90%, and the reflectivity of the low reflectivity grating 5 is ≤20%.

[0033] The cladding pump absorption coefficient of the gain optical fiber 4 at the peak wavelength is 0.2 dB / m to 2.5 dB / m. If the cladding pump absorption coefficient is too large, the loss will also increase at low temperatures.

[0034] Further, the length of the gain fiber matches the central wavelength of the pump source in the pump module at room temperature, wherein the central wavelength of the pump source at room temperature is the absorption coefficient of the central wavelength of the pump source at room temperature at the gain fiber absorption spectrum multiplied by the length of the gain fiber, and the absorption coefficient of the central wavelength of the pump source at room temperature at the gain fiber absorption spectrum is 10dB~30dB, that is, the absorption coefficient of the gain fiber absorption spectrum corresponding to the central wavelength of the pump source at room temperature multiplied by the length of the gain fiber, and the result is within the range of 10dB~30dB. In this way, it can be ensured that there is appropriate absorption at room temperature. The absorption coefficient of the central wavelength of the pump source at room temperature at the gain fiber absorption spectrum should not be too small, nor too large, otherwise the efficiency will decrease at low temperatures.

[0035] The optical fiber output end cap 7 is used to output the laser to the outside of the optical fiber for subsequent measurement or application. The optical fiber output end cap 7 is made of quartz material and has a structure that expands the optical fiber core light to a certain extent.

[0036] The following is based on Figure 2 The structure shown gives a specific embodiment 1 of the present invention: a low temperature operating fiber laser, wherein: The front pump module 1-1: uses a non-wavelength locked semiconductor laser with a central wavelength of 940nm at room temperature as a pump source, the pump source output pigtail is 105 / 125μm, the output power of a single pump source is 250W, there are 6 pump sources in total, and the central wavelength of each pump source at room temperature is located in the valley area on the right side of the gain fiber absorption peak; The front pump coupler 2-1 adopts a (6+1)×1 forward pump signal combiner, the pump arm fiber is 105 / 125μm, the signal arm fiber is 20 / 400μm double-clad fiber, and the output end fiber is 20 / 400μm double-clad fiber; The high reflectivity grating 3 has a central wavelength of 1070 nm, a 3dB bandwidth of 3 nm, a reflectivity of 99%, and a fiber size of 20 / 400 μm double-clad fiber; The gain fiber 4: adopts a three-clad ytterbium-doped fiber with a size of 20 / 400 / 420 μm, the second cladding is a low-refractive-index quartz optical material doped with fluorine, the inner cladding absorption coefficient is 0.3 dB / m@940 nm, the fiber length is 42 m, and the total absorption coefficient at room temperature is 12.6 dB; The low reflectivity grating 5 has a central wavelength of 1070 nm, a 3dB bandwidth of 1 nm, a reflectivity of 10%, and a fiber size of 20 / 400 μm double-clad fiber; The cladding light filter 6 has a cladding light filtering capability of 20 dB and a fiber size of 20 / 400 μm double-clad fiber; The optical fiber output end cap 7: a quartz head, the pigtail size is 20 / 400 μm double-clad optical fiber; By using this embodiment, a 1070nm band laser with an output power of about 1kW can be obtained, and the power fluctuation is less than 5% in the temperature range of -50℃~+20℃. The gain fiber cladding absorption characteristics of the laser are as follows: Figure 6 As shown, its cladding background loss (@1200nm) is lower than Figure 5 The gain fiber used in a conventional laser is shown. Figure 5 The figure below shows the cladding absorption spectrum of the traditional double-clad 20 / 400μm ytterbium-doped fiber as it changes with temperature. Its room temperature absorption coefficient is 2.6dB / m@976nm. On the one hand, since there is no second cladding and the traditional acrylic resin material is used as the outer cladding, the refractive index of the material increases at low temperatures, which reduces the NA of the inner cladding and increases the transmission loss. On the other hand, due to its high doping concentration, defects are easily generated at low temperatures, resulting in transmission loss, which further increases the loss. Therefore, if the traditional double-clad fiber is used directly at low temperatures, the laser efficiency will drop by more than 10%, which is not conducive to practical applications.

[0037] The following is based on Figure 3 The structure shown gives a specific embodiment 2 of the present invention: a low temperature operating fiber laser, wherein: The post-pump module 1-2: uses a non-wavelength-locked semiconductor laser with a central wavelength of 940nm at room temperature as a pump source, the pump source output pigtail is 105 / 125μm, the output power of a single pump source is 250W, there are 6 pump sources in total, and the central wavelength of each pump source at room temperature is located in the valley area on the right side of the gain fiber absorption peak; The post-pump coupler 2-2: adopts a (6+1)×1 forward pump signal combiner, the pump arm fiber is 105 / 125μm, the signal arm fiber is 20 / 400μm double-clad fiber, and the output end fiber is 20 / 400μm double-clad fiber; The high reflectivity grating 3 has a central wavelength of 1070 nm, a 3dB bandwidth of 3 nm, a reflectivity of 99%, and a fiber size of 20 / 400 μm double-clad fiber; The gain fiber 4 is a triple-clad ytterbium-doped fiber with a size of 20 / 400 / 420 μm, an absorption coefficient of 0.3 dB / m@940 nm, and a fiber length of 42 m. The low reflectivity grating 5 has a central wavelength of 1070 nm, a 3dB bandwidth of 1 nm, a reflectivity of 10%, and a fiber size of 20 / 400 μm double-clad fiber; The cladding light filter 6 has a cladding light filtering capability of 20 dB and a fiber size of 20 / 400 μm double-clad fiber; The optical fiber output end cap 7: a quartz head, the pigtail size is 20 / 400 μm double-clad optical fiber; By using this embodiment, a 1070nm band laser with an output power of about 1kW can be obtained, and the power fluctuation is less than 5% within the temperature range of -50°C to +20°C.

[0038] The following is based on Figure 4 The structure shown gives a specific embodiment 3 of the present invention: a low temperature operating fiber laser, wherein: The front pump module 1-1: uses a non-wavelength locked semiconductor laser with a central wavelength of 1010nm at room temperature as a pump source, the pump source output pigtail is 105 / 125μm, the output power of a single pump source is 250W, there are 3 pump sources in total, and the central wavelength of each pump source at room temperature is located in the valley area on the right side of the gain fiber absorption peak; The front pump coupler 2-1 adopts a (6+1)×1 forward pump signal combiner, the pump arm fiber is 105 / 125μm, the signal arm fiber is 20 / 400μm double-clad fiber, the output end fiber is 20 / 400μm double-clad fiber, and the remaining pump arms are cut at an angle and left hanging; The high reflectivity grating 3 has a central wavelength of 1070 nm, a 3dB bandwidth of 3 nm, a reflectivity of 99%, and a fiber size of 20 / 400 μm double-clad fiber; The gain fiber 4 is a triple-clad ytterbium-doped fiber with a size of 20 / 400 / 420 μm, the second cladding is a low-refractive-index quartz material doped with fluorine, the inner cladding absorption coefficient is 0.3 dB / m@1010 nm, and the fiber length is 42 m. The low reflectivity grating 5 has a central wavelength of 1070 nm, a 3dB bandwidth of 1 nm, a reflectivity of 10%, and a fiber size of 20 / 400 μm double-clad fiber; The post-pump module 1-2: uses a non-wavelength-locked semiconductor laser with a central wavelength of 1010nm at room temperature as a pump source, the pump source output pigtail is 105 / 125μm, the output power of a single pump source is 250W, and there are 3 pump sources in total; The back-pump coupler 2-2 adopts a (6+1)×1 back-pump signal combiner, the pump arm fiber is 105 / 125μm, the signal arm fiber is 20 / 400μm double-clad fiber, the output end fiber is 20 / 400μm double-clad fiber, and the remaining pump arms are cut at an angle and left hanging; The cladding light filter 6 has a cladding light filtering capability of 20 dB and a fiber size of 20 / 400 μm double-clad fiber; The optical fiber output end cap 7: a quartz head, the pigtail size is 20 / 400 μm double-clad optical fiber; By using this embodiment, a 1070nm band laser with an output power of about 1kW can be obtained, and the power fluctuation is less than 5% within the temperature range of -50°C to +20°C.

[0039] Through simulation calculation, using traditional optical fiber and 976nm wavelength pump source for pumping, the output power at room temperature (20°C) is 1268W, and the power at low temperature (-50°C) is reduced to 480W; while the laser designed with the parameters of this embodiment has a calculated output power of 1108W (20°C) ~ 1165W (-50°C), which has better power stability.

[0040] Matters not covered by the present invention are known technologies.

[0041] The technical features of the above embodiments may 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.

[0042] 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 invention. It should be pointed out that, for a person of ordinary skill in the art, several modifications 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.

[0043] 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 may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A low temperature fiber laser, comprising a pump module and a gain fiber, characterized in that: Each pump source in the pump module is a non-wavelength locked semiconductor laser, and the central wavelength of each pump source at room temperature is located in the valley area on the right side of the gain fiber absorption peak, and when the temperature drops to zero degrees or below zero degrees, the central wavelength of each pump source moves to a short wave, thereby ensuring that when the temperature drops to zero degrees or below zero degrees, the central wavelength of the pump source drifts, resulting in enhanced pump absorption of the gain fiber.

2. The low temperature fiber laser according to claim 1, characterized in that: The gain optical fiber at least includes a core, a first inner cladding, a second inner cladding and an outer cladding. The core is an active region doped with ytterbium ions. The first inner cladding is a quartz material with a lower refractive index than the core. The second inner cladding is adjacent to the first inner cladding and is a temperature-sensitive low-refractive index material layer, and the refractive index of the material is lower than that of the first inner cladding. The outer cladding is a protective layer of the optical fiber and is a low-refractive index resin material or a metal coating.

3. The low temperature fiber laser according to claim 2, characterized in that: The core of the gain optical fiber is doped with phosphorus and / or aluminum elements to make the peaks and valleys of its absorption spectrum flatter.

4. The low temperature operating fiber laser according to claim 1, 2 or 3, characterized in that: The central wavelength of each pump source in the pump module at room temperature is between 930nm and 950nm or between 1000nm and 1020nm.

5. The low temperature operating fiber laser according to claim 4, characterized in that: The invention also comprises a pump coupler, through which each pump source couples the pump light output by the pump source into the cladding of the gain optical fiber.

6. The low temperature operating fiber laser according to claim 5, characterized in that: One end of the gain optical fiber is connected to a high reflectivity grating, and the other end of the gain optical fiber is connected to a low reflectivity grating. The high reflectivity grating and the low reflectivity grating constitute two end faces of the resonant cavity.

7. The low temperature operating fiber laser according to claim 6, characterized in that: The central wavelengths of the high-reflectivity grating and the low-reflectivity grating are consistent and are used to select the laser of the target wavelength for amplification. The reflectivity of the high-reflectivity grating is ≥90%, and the reflectivity of the low-reflectivity grating is ≤20%.

8. The low temperature operating fiber laser according to claim 5, 6 or 7, characterized in that: The cladding pump absorption coefficient of the gain optical fiber at the peak wavelength is 0.2 dB / m to 2.5 dB / m.

9. The low temperature operating fiber laser according to claim 1 or 2 or 3 or 5 or 6 or 7, characterized in that: The length of the gain optical fiber matches the central wavelength of the pump source in the pump module at room temperature, so that the total absorption coefficient reaches 10 dB to 30 dB.

10. The low temperature operating fiber laser according to claim 9, characterized in that: It also includes a cladding light filter and an optical fiber output end cap, which are used to filter the cladding light from the optical fiber, and output the light transmitted through the core as the output laser of the optical fiber laser to the optical fiber output end cap, and the optical fiber output end cap outputs the output laser to space.

Images