A fiber laser amplifier based on multi-groove and pump-gain integration technology

Abstract

This invention discloses a fiber laser amplifier based on multi-groove and pump-gain integrated technology, including a signal light section, a pump light section, a pump-gain integrated fiber, and a coiled region, which provides an effective technical approach or solution for obtaining high-power, high-beam-quality, and low-nonlinearity single-fiber lasers.

Description

Technical Field

[0001] This invention relates to a fiber laser amplifier based on multi-groove and pump-gain integration technology; it can provide an effective technical approach or solution for obtaining high-power, high-beam-quality, and low-nonlinearity single-fiber lasers. Background Technology

[0002] With the development of high-power fiber laser technology, researchers and engineers are constantly exploring and researching to achieve higher power, higher beam quality, and lower nonlinearity in fiber output, resulting in continuous breakthroughs in various technical solutions. Clearly, in order to achieve higher power and beam quality output, obtaining active gain fibers with large mode field characteristics is particularly important. However, to pursue a large mode field while maintaining the few-mode characteristics of the gain fiber, it is necessary to continuously reduce the numerical aperture. However, the current conventional double-clad gain fiber fabrication technology is limited by the precision of refractive index control, making it difficult to fabricate double-clad large-mode-field fibers with a core refractive index <0.06. To achieve precise control of the core refractive index, photonic crystal and photonic bandgap fiber technologies have been developed. Furthermore, to overcome the difficulty of reducing the core numerical aperture and obtain fibers with large mode field diameters and high beam quality in their output lasers, large-mode-field high-order mode filtering or mode control fibers have emerged, such as leaky channel fibers, chiral core-coupled fibers, and large-pitch photonic crystal fibers. However, the above technologies all have complex and difficult manufacturing processes, making it difficult to achieve widespread practical engineering applications.

[0003] Currently, the market primarily uses low numerical aperture (NA≥0.06) step-index fibers (large-mode-area double-clad fibers) with large mode fields as active gain fibers. Their disadvantages include a lack of high-order mode suppression methods, making them prone to generating high-order modes during use, i.e., mode instability. Other types include photonic crystal fibers, photonic crystal rod fibers, leaky channel photonic crystal fibers, and large-pitch photonic crystal fibers. These fibers have complex structures, making fabrication processes complex and extremely difficult, hindering their ability to meet engineering application requirements. Furthermore, they exhibit low compatibility with commonly used step-index fibers, often resulting in high losses due to collapse effects during splicing, making them unsuitable for high-power fiber lasers. Fibers using multi-groove multimode suppression technology are easier to fabricate and implement.

[0004] To achieve higher power, higher beam quality, and lower nonlinearity fiber laser output, and to facilitate engineering applications, the inventors conceived of organically combining pump-gain integration and multi-groove multimode suppression techniques. Pump-gain integration significantly improves pump light injection capability, supporting the pump gain required for ultra-high power laser output. Simultaneously, it reduces the brightness requirements of the pump source for active gain fibers, thereby lowering the cost of the optical solution. Multi-groove multimode suppression utilizes symmetrical fibers; through the design of refractive index grooves in the fiber structure, it effectively achieves high coupling loss for higher-order fiber modes, thus suppressing their occurrence. The combination of the two technologies allows the pump light to propagate along the extension direction of the active fiber core when it enters the active fiber from the side. At the same time, due to the mode matching effect (the interaction between the structure of the multi-groove multimode suppression fiber and the pump light), the propagation of the coupled pump light is more likely to be confined to the doped core of the multi-groove active fiber, thereby improving the excitation of the fundamental mode located in the doped core of the active fiber. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a fiber laser amplifier based on multi-groove and pump-gain integrated technology, which overcomes the deficiencies of existing technologies and has a reasonable design.

[0006] To achieve the technical requirements of high-power, high-beam-quality, and low-nonlinearity fiber laser output, two technologies are ingeniously combined: a) a gain-integrated fiber pumping technology is used to provide sufficient pump gain for "high-power" output; b) a multi-groove multimode suppression fiber with a circularly symmetric structure is employed. In terms of fabrication, this not only facilitates the fabrication of large-mode-field (low-nonlinearity) fibers but also achieves good suppression of higher-order modes, which is beneficial for obtaining "high-beam-quality" single-fiber laser output. This combination allows the pump light to enter the active fiber from the side, and the evanescent wave coupling effect of the pump-gain integrated technology enables the coupled pump light to propagate along the extension direction of the active fiber core while, more importantly, being confined to the doped core of the multi-groove active fiber due to the mode-matching effect (the interaction between the structure of the multi-groove multimode suppression fiber and the pump light). This, in turn, enhances the excitation of the fundamental mode located in the doped core of the active fiber.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A high-power fiber laser amplifier based on pump-gain integration and multi-groove multimode suppression technology is used to obtain high-power, beam-quality, and low-nonlinear single-fiber laser output.

[0009] This invention provides a fiber laser amplifier based on multi-groove and pump-gain integration technology, comprising a signal light section, a pump light section, and a pump-gain integrated fiber. The pump-gain integrated fiber includes an active fiber at the center and a pump fiber surrounding the active fiber. The signal light section is used to output signal light into the active fiber of the pump-gain integrated fiber; the pump light section is used to couple pump light into the pump fiber of the pump-gain integrated fiber amplifier; the active fiber is a multi-groove fiber, which includes a doped core at the center, a low-refractive-index fiber ring region, a resonant ring region, and a cladding surrounding the doped core.

[0010] Preferably, the active fiber structure includes a doped fiber core f, a first low-refractive-index fiber ring region e, a second low-refractive-index fiber ring region c, a third low-refractive-index fiber ring region a, a first resonant ring region d, a second resonant ring region b, and a cladding.

[0011] Preferably, the doped fiber core f is located at the center of the active fiber, and a first low-refractive-index fiber ring region e is arranged immediately outside it, which is adjacent to and surrounds the doped fiber core f; a first resonant ring region d is arranged immediately outside the first low-refractive-index fiber ring region e, which is adjacent to and surrounds the first low-refractive-index fiber ring region e; a second low-refractive-index fiber ring region c is arranged immediately outside the first resonant ring region d, which is adjacent to and surrounds the first resonant ring region d; a second resonant ring region b is arranged immediately outside the second low-refractive-index fiber ring region c, which is adjacent to and surrounds the second low-refractive-index fiber ring region c; a third low-refractive-index fiber ring region a is arranged immediately outside the second resonant ring region b, and a quartz cladding is arranged immediately outside the third low-refractive-index fiber ring region a, which is adjacent to and surrounds the third low-refractive-index fiber ring region.

[0012] Preferably, the signal light section includes a single-mode output oscillator, which outputs signal light with a working wavelength that is the wavelength of stimulated emission light of rare earth ions. The output fiber of the signal light section is fused with the active fiber of the pump-gain integrated fiber using a mode matcher with low insertion loss, and the signal light is injected into the pump-gain integrated fiber amplifier to achieve signal light injection.

[0013] Preferably, the pump light section may include two sets of pump light output sections, namely a first pump light output section and a second pump light output section; the first pump light output section corresponds to the forward input of the pump fiber of the pump-gain integrated fiber, while the second pump light output section corresponds to the reverse input of the pump fiber of the pump-gain integrated fiber.

[0014] Preferably, for each pump light output section, such as the first pump light output section, since the pump-gain integrated fiber has 8 pump fibers, each pump fiber corresponds to a set of pump sources in the forward direction. Each set of pump sources is formed by combining multiple pump sources through an optical fiber pump combiner. The output pigtail of the pump combiner is then fused to each of the 8 pump fibers in the pump-gain integrated fiber to realize the pump injection of pump light into the pump-gain integrated fiber.

[0015] The second pump light output section can preferably be configured in the same way as the first pump light output section. The pump-gain integrated fiber has 8 pump fibers, each pump fiber corresponding to a set of pump sources in reverse. Each set of pump sources is formed by combining multiple pump sources through an optical fiber pump combiner. The output pigtail of the pump combiner is then fused to each of the 8 pump fibers in the pump-gain integrated fiber to realize the pump injection of pump light into the pump-gain integrated fiber.

[0016] Preferably, the active fiber is an octagonal clad multi-groove fiber, and eight pump fibers are respectively bonded to the eight sides of the active fiber's outer cladding. Preferably, the octagon can be a regular octagon or other suitable shape. The pump light can be coupled or introduced from the pump fiber to the active fiber using the evanescent wave coupling effect generated by the bonding of the pump fiber and the active fiber cladding.

[0017] Preferably, the active fiber core is ytterbium ion doped, the total length of the active fiber is 15-35m, the diameter of the f region of the doped core is 25-50μm, and the cladding diameter can be 300-700μm.

[0018] Preferably, the single-side wall thickness of the first low-refractive-index fiber ring region is 1.5μm-2.5μm, the single-side wall thickness of the second low-refractive-index fiber ring region c is 1.5μm-2.5μm, the single-side wall thickness of the third low-refractive-index fiber ring region a is 1.5μm-2.5μm, the material of the first resonant ring region d is pure silica with a single-side wall thickness of 6μm-10μm, the material of the second resonant ring region b is pure silica with a single-side wall thickness of 6μm-10μm, the diameter of the active fiber silica cladding g = 400μm, and the pump fiber in the pump-gain integrated fiber has a diameter h = 250μm and an NA of 0.46.

[0019] Preferably, it includes a coiled region, which is a section of the pump-gain integrated optical fiber that is bent and coiled to improve the high-order mode filtering effect of the active fiber multi-groove structure.

[0020] A pump-gain integrated optical fiber includes an active fiber at its center and a pump fiber surrounding the active fiber. The active fiber structure includes a doped fiber core f, a first low-refractive-index fiber ring region e, a second low-refractive-index fiber ring region c, a third low-refractive-index fiber ring region a, a first resonant ring region d, a second resonant ring region b, and an outer cladding. The doped fiber core f is located at the center of the active fiber, and the first low-refractive-index fiber ring region e is disposed adjacent to it on its outer side. The first low-refractive-index fiber ring region e is adjacent to and surrounds the doped fiber core f. The first resonant ring region d is disposed adjacent to the outer side of the first low-refractive-index fiber ring region e. A first low-refractive-index fiber ring region e is located close to and surrounds the first resonant ring region d; a second low-refractive-index fiber ring region c is located adjacent to the outside of the first resonant ring region d, and the second low-refractive-index fiber ring region c is located adjacent to the outside of the second low-refractive-index fiber ring region c, and the second resonant ring region b is located adjacent to and surrounds the second low-refractive-index fiber ring region c; a third low-refractive-index fiber ring region a is located adjacent to the outside of the second resonant ring region b, and a cladding is located adjacent to and surrounds the third low-refractive-index fiber ring region a; eight pump fibers are respectively bonded to the cladding of the active fibers.

[0021] The beneficial effects of this invention are:

[0022] 1. This invention provides a fiber laser amplifier based on multi-groove and pump-gain integrated technology, organically and ingeniously combining the two technologies: a) employing gain-integrated fiber pumping technology to provide sufficient pump gain for obtaining "high power" output; b) using multi-groove multimode suppression fiber with a circularly symmetrical structure. In terms of fabrication, this not only facilitates the fabrication of large mode field (low nonlinearity) fibers but also achieves good suppression of higher-order modes, which is beneficial for obtaining "high beam quality" single-fiber laser output. The combination of these two technologies allows the pump light to enter the active fiber from the side, and the evanescent wave coupling effect of the pump-gain integrated technology enables the coupled pump light to propagate along the extension direction of the active fiber core while, more importantly, being confined to the doped core of the multi-groove active fiber due to the mode matching effect (the interaction between the structure of the multi-groove multimode suppression fiber and the pump light), thereby improving the excitation of the fundamental mode located in the doped core of the active fiber.

[0023] 2. The radially alternating annular refractive index regions in the optical fiber can effectively filter out higher-order modes. This is mainly due to the fact that the higher-order mode laser in the fiber core can achieve phase matching with the mode in the resonant annular region, i.e., higher-order mode coupling. Therefore, this resonant annular region can filter out the higher-order modes in the active fiber core, forming leakage modes and suppressing higher-order modes within the core, thus optimizing the core mode.

[0024] 3. The total internal reflection effect generated by multiple low-refractive-index fiber ring regions, especially the first low-refractive-index fiber ring region, acting as the external low-refractive-index interface of the active fiber's doped core, effectively confines most of the pump light and the vast majority of the fundamental mode signal light within the doped core of the active fiber. Higher-order light, however, can overcome the confinement effect of the multiple grooves and escape the doped core region of the active fiber, thereby reducing the amplification of higher-order modes and separating their influence.

[0025] 4. A section of the pump-gain integrated fiber is bent and coiled. Due to reflections from the multilayer low-refractive-index fiber ring, especially the interface reflections of the first low-refractive-index fiber ring, the light beam is confined to the core doped region at the interface. This allows the pump light to repeatedly pass through the core doped region as it travels through this coiled section, increasing the distance the pump light travels through the core doped region (increasing the path distance increases pump efficiency) and making the pumping effect more uniform across the core doped region. Furthermore, the reflections from the multilayer low-refractive-index fiber ring make the confinement of the pump and signal light more reliable and stable. Compared to ordinary bent fibers, this significantly improves light confinement, reduces optical loss, and increases optical efficiency. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the prior art will be briefly introduced below.

[0027] Figure 1 This is a schematic diagram of the high-power fiber laser amplifier based on pump-gain integration and multi-groove multimode suppression technology of the present invention;

[0028] Figure 2 This is a schematic diagram of the structure of a pump-gain integrated optical fiber;

[0029] Figure 3 This is a schematic diagram of the structure of an active fiber with integrated pump-gain;

[0030] Figure 4 This is a schematic diagram of the pump fiber structure of the pump-gain integrated optical fiber;

[0031] Figure 5 This is a schematic diagram of the pump structure of a pump-gain integrated optical fiber. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0033] This invention provides a high-power fiber laser amplifier based on integrated pump-gain and multi-groove multimode suppression technology to obtain high-power, beam-quality, and low-nonlinear single-fiber laser output.

[0034] See Figure 1 The fiber amplifier includes a signal light section 10, a pump light section 20, a pump-gain integrated fiber 30, and a coiled area 40.

[0035] The signal light section preferably includes a near-single-mode output oscillator, through which the signal light is output. The preferred operating wavelength is the wavelength of stimulated emission light from rare-earth ions such as ytterbium, thulium, erbium, and holmium. For example, the preferred operating wavelength is the wavelength of stimulated emission light from ytterbium ions, preferably 1080 nm. Preferably, the output fiber of the signal light section can be an optical fiber with an NA of 0.075, a core diameter of 10 μm, and a cladding diameter of 125 μm. To achieve amplified signal light output, this output fiber is fused with the central active fiber of the pump-gain integrated fiber using a mode matcher with low insertion loss, and the signal light is injected into the pump-gain integrated fiber amplifier. The fiber fusion can be performed using a CO2 laser or electrode discharge fusion method to fuse the two parts.

[0036] The signal light section is used to output the signal light to the central active fiber of the pump-gain integrated optical fiber 30.

[0037] The pump light section 20 includes multiple sets of laser diode (LD) semiconductor lasers. Preferably, the pump light wavelength is the pump wavelength that can excite rare earth ions such as ytterbium, thulium, erbium, and holmium. Preferably, the pump light wavelength is the pump wavelength of ytterbium ions, which is 915 or 976 nm.

[0038] Preferably, the pump light section may include multiple sets of pump light output sections, preferably including two sets of pump light output sections, namely a first pump light output section 1 and a second pump light output section 2; preferably, each pump light output section includes 8 sets of laser diode (LD) semiconductor lasers, as shown in the figure. Figure 5 The first pump light output section 1 corresponds to the forward input of the 8 pump fibers of the integrated pump gain fiber, while the second pump light output section 2 corresponds to the reverse input of the 8 pump fibers of the integrated pump gain fiber.

[0039] Preferably, each group of laser diode semiconductor lasers includes one or more laser diode semiconductor lasers, wherein the output fiber of a single laser diode semiconductor laser module in the pump light section is preferably selected from one of the three standard pump fibers: 105 / 125 / 0.22, 135 / 155 / 0.22, and 200 / 220 / 0.22.

[0040] Preferably, for each pump light output section, such as the first pump light output section, since the pump-gain integrated fiber has 8 pump fibers, each pump fiber corresponds to a set of pump sources in the forward direction. Each set of pump sources is formed by combining multiple pump sources through an optical fiber pump combiner. The output pigtail of the pump combiner is then fused with the corresponding pump fiber among the 8 pump fibers in the pump-gain integrated fiber to realize the pump injection of pump light into the pump-gain integrated fiber.

[0041] The second pump light output section can preferably be configured in the same way as the first pump light output section. The pump-gain integrated fiber has 8 pump fibers, each pump fiber corresponding to a set of pump sources in reverse. Each set of pump sources is formed by combining multiple pump sources through an optical fiber pump combiner. The output pigtail of the pump combiner is then fused with the corresponding pump fiber among the 8 pump fibers in the pump-gain integrated fiber to realize the pump injection of pump light into the pump-gain integrated fiber.

[0042] First, multiple LD pump lasers from one group of LD semiconductor lasers in each pump light output section are combined and coupled to the corresponding pump fiber in the pump-gain integrated fiber. This process is repeated to inject pump light into the pump-gain integrated fiber amplifier and provide gain.

[0043] The pump light section is used to couple the pump light into the pump fiber of the pump-gain integrated fiber amplifier.

[0044] Pump-gain integrated (active) fiber 30 (see Figure 2 The fiber includes an active fiber 31 at the center, a pump fiber 32 surrounding the active fiber, and a coating layer (not shown, but sometimes omitted). Preferably, the fiber is coated during the drawing process while ensuring the signal fiber and pump fiber are in close contact. Except for the contact area, which lacks coating material, the other areas are filled with coating material; therefore, the coating layer is not shown in the figure. After coating the pump-gain integrated fiber... Figure 2The gaps around the pump fiber and signal fiber shown are filled with a low-refractive-index coating material that extends to the outside of the eight pump fibers, thus forming a coating structure similar to that of ordinary optical fibers. Light transmission between the signal and pump fibers occurs only through the bonding area between the two fibers. This design effectively fixes the relative positions of the pump and active fibers, preventing positional shifts and gaps caused by environmental factors or device vibrations. This effectively prevents a decrease in coupling efficiency due to positional shifts and gaps, while also providing better protection for both the active and pump fibers as a whole. Preferably, the active fiber core 31 is ytterbium-doped (or thulium, erbium, holmium, or other rare-earth ion doped). Preferably, the total length of the active fiber is 15–35 m. The inventors realized that when coupled from the side, the circular cladding, due to its small contact area, is not conducive to evanescent wave coupling and will cause significant coupling loss. Preferably, the active fiber cladding is octagonal, which allows the edges of the active fiber to better match the size of the pump fiber, thus enabling the fiber core to absorb pump light more effectively (the contact between a circular surface and a plane improves mode matching and reduces interface loss compared to the contact between two circular surfaces). Preferably, the absorption coefficient of the active fiber for pump light is approximately 0.5 dB / m@915 nm and 1.5 dB / m@976 nm. During the fiber drawing process, coating is performed while ensuring that the signal fiber and pump fiber are in close contact. Except for the bonding area, which has no coating material, other areas are filled with coating material. The pump fiber is preferably circular in structure and may include or not include a cladding. The outer coating of the pump fiber is preferably integrated with the coating of the active fiber, and the eight pump fibers are respectively bonded to the eight edges of the outer cladding of the active fiber. Therefore, the pump light can be coupled or guided from the pump fiber to the active fiber using the evanescent wave coupling effect generated by the bonding of the pump fiber and the active fiber cladding. Preferably, when a coating is present, the pump-gain integrated fiber coating is composed of an acrylic resin material with a low refractive index. Preferably, the diameter of the coating is 600-1400 μm, and more preferably 1000 μm.

[0045] Preferably, the active fiber 31 is a multi-groove fiber, including a doped fiber core located at the center, multiple low-refractive-index fiber ring regions located around the doped fiber core, one or more resonant ring regions, and a cladding.

[0046] Preferably, the active fiber 31 is an octagonal clad multi-groove optical fiber (e.g., Figure 3The active fiber 31 structure mainly includes a doped fiber core f, three radially alternating low-refractive-index fiber ring regions (the first low-refractive-index fiber ring region e, the second low-refractive-index fiber ring region c, and the third low-refractive-index fiber ring region a), a first resonant ring region d, a second resonant ring region b, and a quartz cladding. Preferably, the doped fiber core f is located at the center of the active fiber, and a first low-refractive-index fiber ring region e is arranged immediately outside it, which is adjacent to and surrounds the doped fiber core f; a first resonant ring region d is arranged immediately outside the first low-refractive-index fiber ring region e, which is adjacent to and surrounds the first low-refractive-index fiber ring region e; a second low-refractive-index fiber ring region c is arranged immediately outside the first resonant ring region d, which is adjacent to and surrounds the first resonant ring region d; a second resonant ring region b is arranged immediately outside the second low-refractive-index fiber ring region c, which is adjacent to and surrounds the second low-refractive-index fiber ring region c; a third low-refractive-index fiber ring region a is arranged immediately outside the second resonant ring region b, and a quartz cladding is arranged immediately outside the third low-refractive-index fiber ring region a, which is adjacent to and surrounds the third low-refractive-index fiber ring region.

[0047] In industrial fiber optic amplifiers, two key performance parameters are output power and energy efficiency. Therefore, many inventions aim to improve these two aspects. Typically, improving pump efficiency and energy efficiency reduces fiber temperature, thus lowering fiber mode instability and thermal damage (excessive fiber temperature causes mode instability and thermal damage), and also reduces energy loss (energy loss is a primary concern in industrial applications for high-power lasers, and optical-to-optical conversion efficiency is a crucial indicator of laser advancement). To achieve this, improving optical-to-optical conversion efficiency is particularly important. This requires the pump light to first travel as far as possible along the fiber core direction within the doped fiber core. The pump light propagates through various doped regions of the fiber core, with a large overlap between its propagation area and the doped fiber core along the fiber's extension direction, facilitating efficient utilization. Simultaneously, it is desirable to confine the pump light as much as possible within the doped fiber core region of the active fiber, minimizing external pump light. Firstly, pump light outside the doped fiber core region cannot effectively pump the fundamental mode light; secondly, pump light propagating outside the doped fiber core becomes stray light that needs filtering, making stray light filtering difficult. Furthermore, pump light propagating along the fiber's extension direction, maximizing overlap with the doped fiber core, can effectively pump and amplify the signal's fundamental mode light. The inventors realized that when using such... Figure 2When the pump light enters the active fiber from the side, the evanescent wave coupling effect allows the coupled pump light to propagate along the extension direction of the active fiber core while being more likely to be confined to the doped core of the active fiber due to the mode matching effect (the interaction between the multi-groove structure of the multi-groove multimode suppression fiber and the pump light), thereby improving the excitation of the fundamental mode located in the doped core of the active fiber.

[0048] Preferably, the diameter of the doped fiber core f region is 25-50 μm, and more preferably, the diameter of the doped fiber core f region is 30 μm; preferably, the refractive index of the doped fiber core f is 1.45; preferably, the numerical aperture of the active fiber is 0.066.

[0049] Preferably, the refractive index of the first low-refractive-index fiber ring region e is 1.4485, preferably, the single-side wall thickness is 1.5μm-2.5μm, preferably, the single-side wall thickness is 2μm; preferably, the refractive index of the second low-refractive-index fiber ring region c is 1.4485, preferably, the single-side wall thickness is 1.5μm-2.5μm, preferably, the single-side wall thickness is 2μm; preferably, the refractive index of the third low-refractive-index fiber ring region a is 1.4485, preferably, the single-side wall thickness is 1.5μm-2.5μm, preferably, the single-side wall thickness is 2μm.

[0050] Therefore, in addition to (a) the evanescent coupling of the multi-groove structure and the pump light, which confines the pump light as much as possible within the doped core of the active fiber due to mode matching, (b) the total internal reflection effect generated by the multiple low-refractive-index fiber ring regions, especially the first low-refractive-index fiber ring region, acting as the external low-refractive-index interface of the doped core of the active fiber, effectively confines most of the pump light and the vast majority of the fundamental mode signal light within the doped core of the active fiber. Higher-order light, however, can overcome the confinement effect of the multi-groove structure and escape the doped core region of the active fiber, thereby reducing the amplification effect of higher-order modes and separating their influence. Based on the combined effect of these two reasons, the excitation efficiency of the fundamental mode light and the coupling efficiency of the signal light can be greatly improved, and good separation from higher-order light can be achieved.

[0051] Preferably, the first resonant ring region d is made of pure quartz, preferably, the wall thickness on one side is 6μm-10μm, preferably, the wall thickness on one side is 8μm; preferably, the second resonant ring region b is made of pure quartz, preferably, the wall thickness on one side is 6μm-10μm, preferably, the wall thickness on one side is 8μm.

[0052] The radially alternating annular refractive index regions in this optical fiber effectively filter out higher-order modes. This is primarily achieved by utilizing the phase matching between the higher-order laser modes in the fiber core and the modes in the resonant annular regions, i.e., higher-order mode coupling. Thus, the resonant annular regions filter out the higher-order modes in the active fiber core, forming leakage modes and suppressing higher-order modes within the core, thereby optimizing the core mode. Even when the fiber is bent and coiled, this active fiber achieves a transmission loss of approximately 10 dB / m for higher-order modes and 0.03 dB / m for the fundamental mode. Therefore, this fiber has a significant advantage in obtaining high-beam-quality lasers.

[0053] One significant problem that the active fiber 31, employing multi-groove multimode suppression fiber, can solve is reducing the insertion loss between the active fiber and the signal fiber. Other commonly used multimode suppression fibers (photonic crystal fiber, photonic crystal rod fiber, leaky channel photonic crystal fiber, large-pitch photonic crystal fiber) and signal fibers often suffer from high fusion splicing insertion loss due to significant structural differences and mode mismatch, resulting in reduced overall amplification and energy loss. The inventors recognized the excellent fusion splicing compatibility between multi-groove multimode suppression fiber and commonly used step-index fiber. In this invention, coupling loss can be significantly reduced. The signal output fiber is fusion spliced ​​with the pump-gain integrated central active fiber using a mode matcher with low insertion loss, and the signal light is injected into the pump-gain integrated fiber amplifier, achieving signal light injection and significantly reducing signal light coupling loss.

[0054] Preferably, the active fiber quartz cladding diameter g is 300-700 μm, more preferably 400 μm or more preferably 500 μm.

[0055] Preferably, the pump fiber 32 (with) in the pump-gain integrated optical fiber Figure 4 The pump fiber is a coreless silica fiber, preferably without a cladding (i.e., the air contact interface of the fiber functions as the cladding) to improve pump light coupling efficiency. Preferably, the pump fiber 32 has a diameter of 200-360 μm, and more preferably, a diameter of h = 250 μm and an NA of 0.46. Preferably, the pump fiber can be drawn from a pure silica preform. These eight pump fibers provide eight forward and eight reverse pump light injection points for the pump-gain integrated fiber, significantly reducing the brightness requirements of the pump light. Preferably, the active fiber can also be other polygonal shapes, such as a 9-sided shape, and the corresponding pump fiber can be nine fibers; the active fiber can also be a 12-sided shape, and the corresponding pump fiber can be twelve fibers. Increasing the number of pump fibers improves the pump light injection capability.

[0056] Since the pump light is not necessarily uniform when propagating along the extension direction of the active fiber, some core doped regions of the active fiber may not receive sufficient pumping, leading to a decrease in pump efficiency and uneven gain. To address this, a section of the pump-gain integrated fiber can be bent and coiled. Due to reflections from the multilayer low-refractive-index fiber loop, especially the interface reflections of the first low-refractive-index fiber loop, the beam is confined to the core doped region at the interface. This allows the pump light to traverse the core doped region repeatedly during its coiling, increasing the distance the pump light travels through the core doped region (increasing the path distance increases pump efficiency) and making the pumping degree more uniform across the core doped region. Furthermore, the reflections from the multilayer low-refractive-index fiber loop make the confinement of the pump and signal light more reliable and stable, significantly improving light confinement, reducing optical loss, and increasing optical efficiency compared to ordinary bent fibers.

[0057] Preferably, the coiling region 40 is a section of the pump-gain integrated optical fiber that is bent and coiled. The presence of this coiled section significantly improves the filtering effect of higher-order modes in the active fiber multi-groove structure. Preferably, the coiling diameter of this section is 7–15 cm, and the number of coils is 4–10. Higher-order modes are more likely to escape from the fiber core when the fiber is bent.

[0058] It has high compatibility with existing conventional step-index optical fibers, is easy to splice, has low insertion loss, and facilitates the improvement of photoelectric conversion efficiency; at the same time, it has the characteristics of high power, beam quality, and low nonlinearity.

[0059] The pump-gain integrated fiber described in this patent is applied to a laser oscillator to obtain a high-power single-fiber oscillator laser. The active fiber core can be doped with common rare-earth ions, such as thulium, erbium, and holmium, and this structure enables high-quality laser output.

[0060] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A fiber laser amplifier based on multi-groove and pump-gain integrated technology, characterized in that, The system includes a signal light section, a pump light section, and a pump-gain integrated fiber. The pump-gain integrated fiber includes a central active fiber and a pump fiber surrounding the active fiber. The signal light section outputs the signal light into the active fiber of the pump-gain integrated fiber. The pump light section couples the pump light into the pump fiber of the pump-gain integrated fiber amplifier. The active fiber is a multi-groove fiber, comprising a central doped core, a low-refractive-index fiber ring region, a resonant ring region, and a cladding surrounding the doped core. The active fiber structure includes a doped core f and a first low-refractive-index fiber ring region. e, a second low-refractive-index fiber ring region c, a third low-refractive-index fiber ring region a, a first resonant ring region d, a second resonant ring region b, and a cladding; the doped fiber core f is located at the center of the active fiber, and the first low-refractive-index fiber ring region e is arranged adjacent to it on its outer side. The first low-refractive-index fiber ring region is adjacent to and surrounds the doped fiber core f; the first resonant ring region d is arranged adjacent to the outer side of the first low-refractive-index fiber ring region e. The first resonant ring region d is adjacent to and surrounds the first low-refractive-index fiber ring region e; the second low-refractive-index fiber ring region c is arranged adjacent to the outer side of the first resonant ring region d. The second low-refractive-index fiber ring region c is adjacent to and surrounds the first resonant ring region d. A second resonant ring region b is disposed immediately outside the second low-refractive-index fiber ring region c. The second resonant ring region b is adjacent to and surrounds the second low-refractive-index fiber ring region c. A third low-refractive-index fiber ring region a is disposed immediately outside the second resonant ring region b. A quartz cladding is disposed immediately outside the third low-refractive-index fiber ring region a. The quartz cladding is adjacent to and surrounds the third low-refractive-index fiber ring region. The third low-refractive-index fiber ring region includes a coiled region, which is a section of pump-gain integrated fiber that is bent and coiled to improve the high-order mode filtering effect of the active fiber multi-groove structure.

2. The fiber laser amplifier based on multi-groove and pump-gain integrated technology according to claim 1, characterized in that, The signal light section includes a single-mode output oscillator, which outputs signal light at a wavelength that is the same as the wavelength of stimulated emission light of rare earth ions. The output fiber of the signal light section is fused to the active fiber of the pump-gain integrated fiber through a mode matcher, and the signal light is injected into the pump-gain integrated fiber amplifier to achieve signal light injection.

3. The fiber laser amplifier based on multi-groove and pump-gain integrated technology according to claim 1, characterized in that, The pump light section includes two sets of pump light output sections, namely the first pump light output section and the second pump light output section; the first pump light output section corresponds to the forward input of the pump fiber of the integrated pump-gain fiber, while the second pump light output section corresponds to the reverse input of the pump fiber of the integrated pump-gain fiber.

4. The fiber laser amplifier based on multi-groove and pump-gain integrated technology according to claim 1, characterized in that, The active fiber is an octagonal clad multi-groove fiber. Eight pump fibers are bonded to the eight sides of the active fiber cladding. The pump light is coupled or introduced from the pump fiber to the active fiber by utilizing the evanescent wave coupling effect generated by the bonding of the pump fiber and the active fiber cladding.

5. The fiber laser amplifier based on multi-groove and pump-gain integrated technology according to claim 1, characterized in that, The active fiber core is ytterbium ion doped, the total length of the active fiber is 15-35m, and the cladding diameter is 300-700μm.

6. The fiber laser amplifier based on multi-groove and pump-gain integrated technology according to claim 1, characterized in that, The first low-refractive-index fiber ring region e has a single-side wall thickness of 1.5μm-2.5μm; the second low-refractive-index fiber ring region c has a single-side wall thickness of 1.5μm-2.5μm; the third low-refractive-index fiber ring region a has a single-side wall thickness of 1.5μm-2.5μm; the first resonant ring region d is made of pure silica with a single-side wall thickness of 6μm-10μm; the second resonant ring region b is made of pure silica with a single-side wall thickness of 6μm-10μm; the active fiber silica cladding diameter g = 300-700μm; and the pump fiber in the pump-gain integrated fiber has a diameter h of 200-360μm.

7. The fiber laser amplifier based on multi-groove and pump-gain integrated technology according to claim 1, characterized in that, The diameter of the doped fiber core is 25-50 μm.

8. A pump-gain integrated optical fiber, characterized in that, The active fiber includes an active fiber at its center and a pump fiber surrounding it. The active fiber structure includes a doped fiber core f, a first low-refractive-index fiber ring region e, a second low-refractive-index fiber ring region c, a third low-refractive-index fiber ring region a, a first resonant ring region d, a second resonant ring region b, and an outer cladding. The doped fiber core f is located at the center of the active fiber, and the first low-refractive-index fiber ring region e is located adjacent to it on its outer side. The first low-refractive-index fiber ring region e is adjacent to and surrounds the doped fiber core f. The first resonant ring region d is located adjacent to the outer side of the first low-refractive-index fiber ring region e. The second low-refractive-index fiber ring region c is located adjacent to the outer side of the first resonant ring region d. The second low-refractive-index fiber ring region c is adjacent to and surrounds the first resonant ring region d. A second resonant ring region b is located immediately outside the second low-refractive-index fiber ring region c. The second resonant ring region b is adjacent to and surrounds the second low-refractive-index fiber ring region c. A third low-refractive-index fiber ring region a is located immediately outside the second resonant ring region b. A cladding is located immediately outside the third low-refractive-index fiber ring region a. The cladding is adjacent to and surrounds the third low-refractive-index fiber ring region. The active fiber is an octagonal clad multi-groove fiber, and eight pump fibers are respectively bonded to the cladding of the active fiber. The active fiber includes a coiled region, which is a section of the pump-gain integrated fiber that is bent and coiled to improve the high-order mode filtering effect of the multi-groove structure of the active fiber.

9. The pump-gain integrated optical fiber according to claim 8, characterized in that, The diameter of the doped fiber core f is 25-50μm. The single-side wall thickness of the first low-refractive-index fiber ring region e is 1.5μm-2.5μm. The single-side wall thickness of the second low-refractive-index fiber ring region c is 1.5μm-2.5μm. The single-side wall thickness of the third low-refractive-index fiber ring region a is 1.5μm-2.5μm. The material of the first resonant ring region d is pure silica, with a single-side wall thickness of 6μm-10μm. The material of the second resonant ring region b is pure silica, with a single-side wall thickness of 6μm-10μm. The diameter of the active fiber silica cladding g is 300-700μm. The pump fiber in the pump-gain integrated fiber has a diameter h of 200-360μm.

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