CN115663578A - Optical fiber laser amplifier based on multi-gully and pumping-gain integrated technology - Google Patents

Abstract

The invention discloses an optical fiber laser amplifier based on multi-gully and pumping-gain integrated technology, which comprises a signal light part, a pumping-gain integrated optical fiber and a coiling region, and is used for providing an effective technical approach or scheme for obtaining single-fiber laser with high power, high beam quality and low nonlinearity.

Description

Optical fiber laser amplifier based on multi-gully and pumping-gain integrated technology

Technical Field

The invention relates to an optical fiber laser amplifier based on multi-gully and pumping-gain integrated technology; it can provide an effective technical approach or scheme for obtaining single-fiber laser with high power, high beam quality and low nonlinearity.

Background

With the development of high-power fiber laser technology, related scientific research and engineering technicians are constantly under research and exploration for continuously pursuing higher-power, higher-beam-quality and low-nonlinearity fiber output, and continuous breakthrough is realized on each technical scheme. It is obvious that, in the technology, it is important to obtain an active gain fiber with large mode field characteristics in order to achieve higher power and beam quality output. However, in order to pursue a large mode field while maintaining the few-mode characteristics of the gain fiber, it is necessary to continuously decrease the numerical aperture, which is limited to the control precision of the refractive index by the conventional double-clad gain fiber manufacturing technology at present, making it difficult to manufacture a double-clad large-mode-field fiber with a core number < 0.06. In order to realize precise control of the refractive index of the fiber core, certain developments have been made in photonic crystal and photonic band gap fiber technologies. In addition, in order to overcome the problem that the numerical aperture of the core cannot be reduced and obtain an optical fiber with a large mode field diameter, and enable the output laser to have high beam quality, a large mode field high-order mode filtering or mode control optical fiber is derived, for example: leakage channel fiber, chiral core coupling fiber, large-spacing photonic crystal fiber, etc. However, the above techniques have the disadvantages of complex preparation process and difficulty, and are difficult to realize wide practical engineering application.

The existing market mainly adopts a step-index optical fiber (large-mode-field double-clad optical fiber) with a large mode field and a low numerical aperture (NA is more than or equal to 0.06) as an active gain fiber. The disadvantages are as follows: high-order mode suppression means is absent, and high-order modes, namely mode instability, are easily generated in the using process. Photonic crystal fibers, photonic crystal rod fibers, leakage channel photonic crystal fibers, large-pitch photonic crystal fibers, and the like. The structure of the optical fiber is complex, so that on one hand, the preparation process is complex and difficult, and the engineering application requirements are difficult to meet; on the other hand, the compatibility of the optical fiber with the current commonly used refractive index step type optical fiber is lower, the loss is higher due to the collapse effect in the fusion process, and the optical fiber is difficult to be applied to the aspect of high-power optical fiber laser. The manufacturing difficulty of the optical fiber corresponding to the multiple-gully and multiple-mode restraining technology is low, and the optical fiber is easier to obtain and realize in the manufacturing process.

In order to better obtain higher power, higher beam quality, low nonlinear fiber laser output and make the technical scheme easier to realize engineering application. The inventor thinks of organically combining the pump-gain integration technology and the multi-channel multi-mode suppression technology. The pump-gain integration technology can improve the injection capability of pump light to a great extent and can support the pump gain required by the output of ultrahigh-power laser. Meanwhile, the brightness requirement of the active gain fiber on the pumping source is reduced, and the cost of the optical scheme is further reduced. The optical fibers corresponding to the multi-gap multimode suppression technology are symmetrical, and high coupling loss can be well realized for a high-order optical fiber mode through the refractive index gap design of the optical fiber structure, so that the occurrence of the high-order mode is suppressed. The combination of the two enables that when the pump light enters the active fiber from the side surface of the active fiber, the evanescent coupling effect of the pump-gain integration technology enables the propagation mode of the coupled pump light to propagate along the extension direction of the active fiber core, and simultaneously, the propagation mode of the coupled pump light is more likely to be limited at the doped fiber core of the multi-ravine active fiber due to the mode matching effect (the interaction between the structure of the multi-ravine multi-mode suppression fiber and the pump light), so as to improve the excitation of the fundamental mode of the doped fiber core of the active fiber.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides the optical fiber laser amplifier based on the multi-gully and pumping-gain integrated technology, which overcomes the defects of the prior art and has reasonable design.

The technical requirements of high power, high beam quality and low nonlinear fiber laser output are met. Organically and skillfully combining the two technologies, a, providing sufficient pumping gain for obtaining high-power output by adopting a gain-integrated optical fiber pumping technology; b. the multi-channel multi-mode restraining optical fiber with the circular symmetrical structure is adopted, so that the preparation of the large-mode-field (low-nonlinearity) optical fiber can be easily realized in the preparation aspect, the high-order mode can be well restrained, and the single-fiber laser output with high beam quality can be favorably obtained. The combination of the two enables that, when the pump light enters the active fiber from the side surface of the active fiber, the evanescent coupling effect of the pump-gain integration technology enables the propagation mode of the coupled pump light to propagate along the extension direction of the active fiber core, and simultaneously, the propagation mode of the coupled pump light is more likely to be limited to propagate at the doped fiber core of the multi-channel active fiber due to the mode matching effect (the multi-channel multi-mode inhibits the interaction between the structure of the optical fiber and the pump light), so as to improve the excitation of the fundamental mode of the doped fiber core of the active fiber.

In order to achieve the purpose, the invention is realized by the following technical scheme:

a high-power optical fiber laser amplifier based on pumping-gain integration and multi-channel multi-mode suppression technology is used for obtaining high-power, light beam quality and low-nonlinearity single-fiber laser output.

The invention provides an optical fiber laser amplifier based on multi-gully and pump-gain integrated technology, which comprises a signal light part, a pump light part and a pump-gain integrated optical fiber, wherein the pump-gain integrated optical fiber comprises an active fiber positioned in the center and a pump fiber positioned at the periphery of the active fiber; the pump light part is used for coupling the pump light into a pump fiber of the pump-gain integrated optical fiber amplifier; the active fiber is a multi-channel optical fiber, and comprises a doped fiber core in the center, a low-refractive-index fiber ring region, a resonant ring region and a cladding layer, wherein the low-refractive-index fiber ring region, the resonant ring region and the cladding layer are arranged on the periphery of the doped fiber core.

Preferably, the active fiber structure comprises a doped fiber core f, a first low-refractive-index fiber ring area e, a second low-refractive-index fiber ring area c, a third low-refractive-index fiber ring area a, a first resonant ring area d, a second resonant ring area b and a cladding.

Preferably, the doped fiber core f is positioned in the center of the active fiber, a first low-refractive-index fiber ring area e is arranged on the outer side of the active fiber in a close proximity mode, and the first low-refractive-index fiber ring area is close to and surrounds the doped fiber core f; a first resonant ring area d is arranged on the outer side of the first low-refractive-index optical fiber ring area e in an adjacent mode, and the first resonant ring area d is close to and surrounds the first low-refractive-index optical fiber ring area e; a second low-refractive-index optical fiber ring area c is arranged on the outer side of the first resonant ring area d in an adjacent mode, and the second low-refractive-index optical fiber ring area c is close to and surrounds the first resonant ring area d; a second resonance ring area b is arranged on the outer side of the second low-refractive-index optical fiber ring area c in an adjacent mode, and the second resonance ring area b is close to and surrounds the second low-refractive-index optical fiber ring area c; and a third low-refractive-index optical fiber ring area a is arranged on the outer side of the second resonance ring area b in an adjacent manner, a quartz cladding is arranged on the outer side of the third low-refractive-index optical fiber ring area a in an adjacent manner, and the quartz cladding is close to and surrounds the third low-refractive-index optical fiber ring area.

Preferably, the signal light portion includes a single-mode output oscillator, the signal light is output through the single-mode output oscillator, the operating wavelength is the wavelength of the stimulated emission light of the rare-earth ions, the output optical fiber of the signal light portion and the active fiber of the pump-gain integrated optical fiber are subjected to low insertion loss fusion through the mode matcher, and the signal light is injected into the pump-gain integrated optical fiber amplifier to achieve signal light injection.

Preferably, the pump light portion may include two sets of pump light output portions, a first pump light output portion and a second pump light output portion; the first pump light output portion corresponds to a forward input of the pump fiber of the pump gain integrated fiber, and the second pump light output portion corresponds to a reverse input of the pump fiber of the pump gain integrated fiber.

Preferably, for each pump light output part, for example, the first pump light output part, since the pump-gain integrated fiber has 8 pump fibers, each pump fiber corresponds to a group of pump sources in the forward direction, each group of pump sources is formed by combining a plurality of pump sources through a fiber pump combiner, and the output pigtail of the pump combiner is further fused with each of the 8 pump fibers in the pump-gain integrated fiber, so as to realize the pump injection of the pump light into the pump-gain integrated fiber.

The second pump light output part is preferably set as the first pump light output part, 8 pump fibers exist in the pump-gain integrated optical fiber, each pump fiber is reversely corresponding to one group of pump sources, each group of pump sources is formed by combining and bundling a plurality of pump sources through an optical fiber pump beam combiner, and the output tail fiber of the pump beam combiner is welded with each of the 8 pump fibers in the pump-gain integrated optical fiber so as to realize the pump injection of the pump light to the pump-gain integrated optical fiber.

Preferably, the active fiber is an 8-edge clad multi-channel optical fiber, and the 8 pump fibers are respectively attached to 8 edges of the active fiber outer cladding, and preferably, the 8 edge can be a regular octagon or other suitable shapes. The pump light can be coupled or guided from the pump fiber to the active fiber by utilizing evanescent wave coupling effect generated by attaching the pump fiber and the active fiber cladding.

Preferably, the core of the active fiber is doped with ytterbium ions, the total length of the active fiber is 15-35 m, the diameter of the f area of the doped core is 25-50 μm, and the diameter of the cladding can be 300-700 μm.

Preferably, the single-side wall thickness of the first low-refractive-index optical fiber ring area is 1.5-2.5 μm, the single-side wall thickness of the second low-refractive-index optical fiber ring area c is 1.5-2.5 μm, the single-side wall thickness of the third low-refractive-index optical fiber ring area a is 1.5-2.5 μm, the first resonant ring area d is made of pure quartz, and the single-side wall thickness is 6-10 μm; the second resonant ring region b is made of pure quartz, the thickness of a single-side wall of the second resonant ring region b is 6-10 μm, the diameter g =400 μm of the quartz cladding of the active fiber, the diameter h =250 μm of the pumping fiber in the pumping-gain integrated optical fiber, and the NA is 0.46.

Preferably, the optical fiber comprises a coiling region, wherein the coiling region is formed by coiling a section of bent coil of the pump-gain integrated optical fiber and is used for improving the high-order mode filtering effect of the active fiber multi-channel structure.

A pumping-gain integrated optical fiber comprises an active fiber positioned in the center and a pumping fiber positioned at the periphery of the active fiber, wherein the active fiber structure comprises a doped fiber core f, a first low-refractive-index fiber ring area e, a second low-refractive-index fiber ring area c, a third low-refractive-index fiber ring area a, a first resonance ring area d, a second resonance ring area b and an external cladding; a first resonance ring area d is arranged on the outer side of the first low-refractive-index optical fiber ring area e in a close proximity mode, and the first resonance ring area d is close to and surrounds the first low-refractive-index optical fiber ring area e; a second low-refractive-index optical fiber ring area c is arranged on the outer side of the first resonant ring area d in an adjacent mode, and the second low-refractive-index optical fiber ring area c is close to and surrounds the first resonant ring area d; a second resonance ring area b is arranged on the outer side of the second low-refractive-index optical fiber ring area c in an adjacent mode, and the second resonance ring area b is close to and surrounds the second low-refractive-index optical fiber ring area c; a third low-refractive-index optical fiber ring area a is arranged on the outer side of the second resonance ring area b in an adjacent mode, a cladding is arranged on the outer side of the third low-refractive-index optical fiber ring area a in an adjacent mode, and the cladding is close to and surrounds the third low-refractive-index optical fiber ring area; the 8 pumping fibers are respectively attached to the cladding of the active fiber.

The beneficial effects of the invention are:

1. the invention provides an optical fiber laser amplifier based on multi-gully and pumping-gain integrated technology, which organically and skillfully combines the two technologies, and a, the gain-integrated optical fiber pumping technology is adopted to provide enough pumping gain for obtaining high-power output; b. the multi-channel multi-mode restraining optical fiber with the circular symmetrical structure is adopted, so that the preparation of the large-mode-field (low-nonlinearity) optical fiber can be easily realized in the preparation aspect, the high-order mode can be well restrained, and the single-fiber laser output with high beam quality can be favorably obtained. The combination of the two enables that when the pump light enters the active fiber from the side surface of the active fiber, the evanescent coupling effect of the pump-gain integration technology enables the propagation mode of the coupled pump light to propagate along the extension direction of the active fiber core, and simultaneously, the propagation mode of the coupled pump light is more likely to be limited at the doped fiber core of the multi-ravine active fiber due to the mode matching effect (the interaction between the structure of the multi-ravine multi-mode suppression fiber and the pump light), so as to improve the excitation of the fundamental mode of the doped fiber core of the active fiber.

2. The annular refractive index regions which are alternately distributed along the radial direction of the optical fiber can play a high-order mode filtering effect, and the high-order mode laser of the fiber core of the optical fiber structure can be mainly utilized to realize phase matching with the mode of the resonant annular region, namely high-order mode coupling. Therefore, the resonant annular region can filter the high-order mode of the active fiber core to form a leakage mode, and the high-order mode in the fiber core is restrained to play a role in optimizing the fiber core mode.

3. The total reflection effect generated by the plurality of low-refractive-index optical fiber ring regions, particularly the first low-refractive-index optical fiber ring region, acting as the outer low-refractive-index interface of the doped fiber core of the active fiber can effectively limit most of the pump light and most of the fundamental-mode signal light in the doped fiber core of the active fiber. The high-order light can break through the restriction of multiple ravines and can be separated from the restriction of the doped core region of the active fiber, thereby reducing the amplification of the high-order mode and separating the influence of the high-order mode.

4. A section of the pumping-gain integrated optical fiber is bent and coiled, and because the reflection of the multi-layer low-refractive-index optical fiber ring area, particularly the interface reflection of the first low-refractive-index optical fiber ring area, enables the light beam to be reflected at the position of the arriving interface and constrained in the fiber core doping area, so that the pumping light can pass through the fiber core doping area back and forth when being coiled, the distance of the pumping light passing through the fiber core doping area is increased (the path distance of the pumping light passing through the fiber core doping area is increased, the pumping efficiency can be increased), and meanwhile, the pumping degree of each area of the fiber core doping area is more uniform. And the reflection of the multi-layer low-refractive-index optical fiber ring region enables the confinement of the pump light and the signal light to be more reliable and stable, and compared with the common bent optical fiber, the optical confinement capability can be greatly improved, the optical loss is reduced, and the optical efficiency is improved.

Drawings

In order to more clearly illustrate the present invention or the prior art solutions, the drawings that are needed in the description of the prior art will be briefly described below.

FIG. 1 is a schematic diagram of a high power fiber laser amplifier based on pump-gain integration and multi-channel multi-mode suppression technology according to the present invention;

FIG. 2 is a schematic diagram of a pump-gain integrated optical fiber;

FIG. 3 is a schematic diagram of the structure of an active fiber of a pump-gain integrated optical fiber;

FIG. 4 is a schematic diagram of a pump fiber structure of a pump-gain integrated optical fiber;

fig. 5 is a schematic diagram of a pumping structure of the pump-gain integrated fiber.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings.

The embodiment of the invention provides a high-power optical fiber laser amplifier based on pumping-gain integration and multi-channel multi-mode suppression technology, which is used for obtaining high-power, light beam quality and low-nonlinearity single-fiber laser output.

Referring to fig. 1, the optical fiber amplifier includes a signal light section 10, a pump light section 20, a pump-gain integrated optical fiber 30, and a coiling region 40.

The signal light section preferably includes a near-single mode output oscillator through which signal light is output, and the preferred operating wavelength is a wavelength of stimulated emission light of a rare earth ion such as ytterbium, thulium, erbium, holmium, and the like, for example, the preferred operating wavelength is a wavelength of stimulated emission light of ytterbium ion, and is preferably 1080nm. Preferably, the output fiber of the signal light part can adopt a fiber with NA of 0.075, core diameter of 10 μm and cladding diameter of 125 μm. In order to amplify and output the signal light, the output optical fiber and the central active fiber of the pump-gain integrated optical fiber are subjected to low insertion loss fusion by a mode matching device, and the signal light is injected into the pump-gain integrated optical fiber amplifier, thereby realizing signal light injection. The fiber welding can adopt CO2 laser or electrode discharge welding method to weld the two parts.

The signal light portion is used to output signal light into the central active fiber of the pump-gain integrated optical fiber 30.

The pump light part 20 includes multiple Laser Diode (LD) semiconductor lasers, preferably, the pump light wavelength is a pump wavelength capable of exciting excitation light of ytterbium, thulium, erbium, holmium and other rare earth ions, preferably, the pump light wavelength is a pump wavelength of ytterbium ions, and is 915 or 976nm.

Preferably, the pump light portion may comprise a plurality of sets of pump light output portions, preferably two sets of pump light output portions, respectively a first pump light output portion 1, a second pump light output portion 2; preferably, each of the pump light output sections includes 8 sets of Laser Diode (LD) semiconductor lasers, and referring to fig. 5, the first pump light output section 1 corresponds to a forward input of 8 pump fibers of the pump gain integrated fiber, and the second pump light output section 2 corresponds to a reverse input of 8 pump fibers of the pump gain integrated fiber.

Preferably, each group of laser diode semiconductor lasers comprises one or more laser diode semiconductor lasers, wherein the output fiber of a single laser diode semiconductor laser module in the pump light section may be selected as one of three standard pump fibers, 105/125/0.22, 135/155/0.22 and 200/220/0.22.

Preferably, for each pump light output part, for example, the first pump light output part, since there are 8 pump fibers in the pump-gain integrated fiber, each pump fiber corresponds to a group of pump sources in the forward direction, each group of pump sources is formed by combining a plurality of pump sources through a fiber pump combiner, and the output pigtail of the pump combiner is further fused with the corresponding pump fiber in the 8 pump fibers in the pump-gain integrated fiber, so as to realize pump injection of the pump light to the pump-gain integrated fiber.

The second pump light output part is preferably set as the first pump light output part, 8 pump fibers exist in the pump-gain integrated optical fiber, each pump fiber is reversely corresponding to one group of pump sources, each group of pump sources is formed by combining and bundling a plurality of pump sources through an optical fiber pump combiner, and the output tail fiber of the pump combiner is welded with the corresponding pump fiber in the 8 pump fibers in the pump-gain integrated optical fiber, so that the pump injection of the pump light to the pump-gain integrated optical fiber is realized.

Firstly, a plurality of LD pumping lasers in one group of LD semiconductor lasers in each group of pumping light output parts are combined and coupled to corresponding pumping fibers in the pumping-gain integrated optical fiber, and so on, thereby realizing the pumping light injection of the pumping-gain integrated optical fiber amplifier and providing gain.

The pump light part is used for coupling the pump light into a pump fiber of the pump-gain integrated optical fiber amplifier.

The pump-gain integrated (active) fiber 30 (see fig. 2) includes an active fiber 31 at the center, a pump fiber 32 at the periphery of the active fiber, a coating layer (the coating layer is not shown, and may be omitted), and the like, and preferably, the fiber is coated during the drawing process under the condition that the signal fiber and the pump fiber are ensured to be jointed, and the other regions are filled with the coating material except the jointing region without the coating layer material, so that the coating layer is not shown in the figure. After the pump-gain integrated optical fiber is coated, the gaps around the pump fiber and the signal fiber shown in fig. 2 are filled with the low-refractive-index coating material and extend to the outside of 8 pump fibers, so as to form a coating structure the same as that of a common optical fiber. The optical transmission between the signal light and the pumping fiber is only through the joint between the two fibers. The purpose of doing so lies in can be good fixed pumping relative position between the fine and the active fiber, prevent the relative position skew between the two of position and the gap that appears because of reasons such as environment or device rocks between the two, the reduction of the coupling efficiency that has effectively prevented to lead to because of the position skew and the gap between the two, simultaneously can better protection active fiber and pumping fine as a whole. The core of the active fiber 31 is preferably doped with ytterbium ions (of course, rare earth ions such as thulium, erbium, holmium and the like can be doped with ytterbium ions), and the total length of the active fiber is preferably 15-35 m. The inventors have realized that a circular cladding is not conducive to evanescent wave coupling when coupled from the side, and causes large coupling loss due to small contact area, preferably the active fiber cladding is 8-sided to make the sides of the active fiber more conform to the size of the pump fiber to be close to the pump fiber, so that the core obtains more efficient absorption of the pump light (circular surface to plane contact improves mode matching and reduces interface loss compared to two circular surface contact), preferably the absorption coefficient of the pump light by the active fiber is about 0.5dB/m @915nm and 1.5dB/m @976nm. The optical fiber is coated under the condition of ensuring the bonding of the signal fiber and the pump fiber in the drawing process, and coating materials are filled in other areas except the bonding area without the coating material. The pump fiber is preferably a circular structure and may include a cladding or no cladding, the outer cladding of the pump fiber is preferably a coating layer integrated with the active fiber, and 8 pump fibers are respectively attached to 8 edges of the outer cladding of the active fiber, so that the pump light can be coupled or guided from the pump fiber to the active fiber by using an evanescent wave coupling effect generated by attaching the pump fiber to the cladding of the active fiber. Preferably, when having a coating layer, the pump-gain integrated fiber coating layer is composed of an acrylic resin material having a low refractive index, preferably, the coating layer diameter may be 600-1400 μm, preferably, the coating layer diameter is 1000 μm.

Preferably, the active fiber 31 is a multi-channel optical fiber, which includes a doped core located in the center, a plurality of low-index fiber ring regions located at the periphery of the doped core, one or more resonant ring regions, and a cladding.

Preferably, the active fiber 31 is an 8-edge clad multi-gap fiber (see fig. 3), and the structure of the active fiber 31 mainly includes a doped core f, 3 fiber ring regions with low refractive index distribution (a first low refractive index fiber ring region e, a second low refractive index fiber ring region c, and a third low refractive index fiber ring region a) alternately distributed along the radial direction, a first resonance ring region d, a second resonance ring region b, and a quartz cladding. Preferably, the doped fiber core f is positioned in the center of the active fiber, a first low-refractive-index fiber ring area e is arranged on the outer side of the active fiber in a close proximity mode, and the first low-refractive-index fiber ring area is close to and surrounds the doped fiber core f; a first resonant ring area d is arranged on the outer side of the first low-refractive-index optical fiber ring area e in an adjacent mode, and the first resonant ring area d is close to and surrounds the first low-refractive-index optical fiber ring area e; a second low-refractive-index optical fiber ring area c is arranged on the outer side of the first resonant ring area d in an adjacent mode, and the second low-refractive-index optical fiber ring area c is close to and surrounds the first resonant ring area d; a second resonance ring area b is arranged on the outer side of the second low-refractive-index optical fiber ring area c in an adjacent mode, and the second resonance ring area b is close to and surrounds the second low-refractive-index optical fiber ring area c; and a third low-refractive-index optical fiber ring area a is arranged on the outer side of the second resonance ring area b in a closely-adjacent mode, a quartz cladding is arranged on the outer side of the third low-refractive-index optical fiber ring area a in a closely-adjacent mode, and the quartz cladding is close to and surrounds the third low-refractive-index optical fiber ring area.

Two important points considered in the main functional parameters of the industrial optical fiber amplifier are output power and energy utilization rate, therefore, many inventions are expected to improve the effects of the two points, generally, in order to improve the pumping efficiency and the energy utilization rate of the pump light, so as to reduce the temperature of the optical fiber, the mode instability of the optical fiber, the thermal damage of the optical fiber (the mode instability and the thermal damage of the optical fiber are generated when the temperature of the optical fiber is too high), and the energy loss (the energy loss of high-power laser is the most commonly considered point in industrial application, and the optical-to-optical conversion efficiency is an important index for representing whether a laser is advanced or not), and in order to achieve the effect, especially, the optical-to-optical conversion efficiency needs to be improved, the pump light firstly propagates in the direction of the fiber core as much as possible in the doped fiber core, so that the pump light can traverse each doped region of the fiber core, and the overlapping region of the propagation region of the pump light and the doped fiber core along the extending direction of the optical fiber is relatively large, and is beneficial to the effective utilization of the pump light; meanwhile, the pump light is expected to be constrained in the doped fiber core region of the active fiber as much as possible, the pump light at the outside should be as little as possible, firstly, the pump light outside the doped fiber core region cannot effectively pump the fundamental mode light, and secondly, the pump light propagated outside the doped fiber core also becomes stray light to be filtered, so that the problem of high difficulty in filtering stray light is caused; while propagating along the fiber extension direction, the pump light that is as coincident as possible with the doped core may effectively pump and amplify the signal fundamental mode light, and the inventors have realized that when the structure as shown in fig. 2 is adopted, when the pump light enters the active fiber from the side surface through the active fiber, the evanescent coupling effect may enable the propagation mode of the coupled pump light to propagate along the extension direction of the active fiber core while being more likely to be restricted from propagating at the doped core of the active fiber due to the mode matching effect (the multi-ravine multimode inhibits the interaction between the multi-ravine structure of the fiber and the pump light), thereby improving the excitation of the fundamental mode located at the doped core of the active fiber.

Preferably, the doped core f region has a diameter of 25-50 μm, preferably the doped core f region has a diameter of 30 μm; preferably, the doped core f has a refractive index of 1.45; preferably, the active fiber has a numerical aperture of 0.066.

Preferably, the refractive index of the first low-refractive-index optical fiber ring region e is 1.4485, preferably, the single-sided wall thickness is 1.5 μm to 2.5 μm, preferably, the single-sided wall thickness is 2 μm; preferably, the second low-refractive-index optical fiber ring region c has a refractive index of 1.4485, preferably a single-sided wall thickness of 1.5 μm to 2.5 μm, preferably a single-sided wall thickness of 2 μm; preferably, the third low-index optical fiber ring region a has a refractive index of 1.4485, preferably a single-sided wall thickness of 1.5 μm to 2.5 μm, preferably a single-sided wall thickness of 2 μm.

Therefore, in addition to (a) the evanescent wave coupling of the multiple-channel structure and the pump light enables the pump light to be confined in the doped core of the active fiber as much as possible due to the mode matching, and (b) the total reflection effect generated by the plurality of low-refractive-index optical fiber ring regions, especially the first low-refractive-index optical fiber ring region, acting as the outer low-refractive-index interface of the doped core of the active fiber can effectively confine most of the pump light and most of the fundamental-mode signal light in the doped core of the active fiber. The high-order light can break through the restriction of multiple ravines and can be separated from the restriction of the doped core region of the active fiber, thereby reducing the amplification of the high-order mode and separating the influence of the high-order mode. Based on the dual functions of the two reasons, the excitation efficiency of the fundamental mode light and the coupling efficiency of the signal light can be greatly improved, and the fundamental mode light and the high-order light are well separated.

Preferably, the material of the first resonant ring region d is pure quartz, and preferably, the thickness of a single-side wall is 6 μm to 10 μm, and preferably, the thickness of a single-side wall is 8 μm; preferably, the second resonance ring region b is made of pure quartz, and preferably has a single-side wall thickness of 6 μm to 10 μm, and preferably has a single-side wall thickness of 8 μm.

The annular refractive index regions which are alternately distributed along the radial direction of the optical fiber can play a role in filtering high-order modes, and the high-order mode laser of the fiber core of the optical fiber structure can be mainly utilized to realize phase matching with the modes of the resonant annular region, namely high-order mode coupling. Therefore, the resonant annular region can filter the high-order mode of the active fiber core to form a leakage mode, and the high-order mode in the fiber core is restrained to play a role in optimizing the fiber core mode. In the case of the optical fiber bent and coiled, the active fiber can realize about 10dB/m transmission loss for high-order mode, and 0.03dB/m loss for fundamental mode, so the optical fiber has great advantages in obtaining high beam quality laser.

The present inventors have recognized that the good fusion matching between the multi-gully multimode suppression fiber and the commonly used refractive index step fiber can significantly reduce the coupling loss in the present invention, and perform low insertion loss fusion between the signal output fiber and the pump-gain integrated central active fiber through the mode matcher, and inject the signal light into the pump-gain integrated fiber amplifier to realize signal light injection, which can significantly reduce the signal light coupling loss.

Preferably the active fiber silica cladding diameter g is 300-700 μm, preferably the active fiber silica cladding diameter g is =400 μm or preferably the active fiber silica cladding diameter g is =500 μm.

Preferably, the pump fiber 32 (fig. 4) in the pump-gain integrated fiber is a coreless silica fiber, i.e., preferably, the pump fiber has no cladding (i.e., functions as a cladding with the air contact interface of the fiber) to improve the pump light coupling efficiency, preferably, the pump fiber 32 has a diameter of 200-360 μm, preferably, the pump fiber 32 has a diameter h =250 μm, and NA is 0.46. Preferably, the pump fiber can be drawn from a pure quartz preform. The 8 pump fibers can provide 8 forward and 8 backward pump lights for the pump-gain integrated fiber to be injected into the input end of the pump fiber, and the brightness requirement on the pump lights can be reduced to a great extent. Preferably, the active fiber may also adopt other polygonal shapes, such as 9 polygons, the corresponding pump fibers may also adopt 9 polygons, the active fiber may also adopt 12 polygons, and the like, and the corresponding pump fibers may also adopt 12. To improve the pump light injection capability by increasing the number of pump fibers.

Because the pump light is not necessarily uniform when propagating along the extension direction of the active fiber, sometimes some fiber core doped regions of the active fiber cannot necessarily obtain sufficient pumping, which will cause the reduction of pumping efficiency and the nonuniformity of gain, for this reason, a section of the pump-gain integrated fiber can be bent and coiled, and because the reflection of the multi-layer low-refractive-index fiber ring region, especially the interface reflection of the first low-refractive-index fiber ring region, enables the light beam to be reflected at the interface to be confined in the fiber core doped region, so that the pump light can pass through the fiber core doped region back and forth when being coiled, the distance of the pump light passing through the fiber core doped region is increased (the path distance of the pump light passing through the fiber core doped region is increased to increase the pumping efficiency), and simultaneously, the pumping degree of each region of the fiber core doped region is more uniform. And the reflection of the multi-layer low-refractive-index optical fiber ring region enables the confinement of the pump light and the signal light to be more reliable and stable, and compared with the common bent optical fiber, the optical confinement capability can be greatly improved, the optical loss is reduced, and the optical efficiency is improved.

The winding region 40 is preferably a segment of the bent winding of the pump-gain integrated optical fiber, which greatly improves the high-order mode filtering effect of the active fiber multi-channel structure due to the winding segment, and the winding segment is preferably 7-15 cm in winding diameter and 4-10 turns in winding number. Higher order modes are more likely to escape the core when the fiber is bent.

Compared with the conventional step-index optical fiber, the optical fiber has high compatibility, convenient welding, low insertion loss and convenient improvement of photoelectric conversion efficiency; meanwhile, the method has the characteristics of high power, light beam quality and low nonlinearity acquisition.

The pump gain integrated optical fiber in the patent is applied to a laser oscillator to obtain high-power single-fiber oscillator laser. The main core of the active fiber can be doped with common rare earth ions, such as: thulium, erbium, holmium and the like, and the structure is adopted to realize high-quality laser output.

The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims (10)

1. The optical fiber laser amplifier based on multi-gully and pump-gain integration technology is characterized by comprising a signal light part (10), a pump light part (20) and a pump-gain integration optical fiber (30), wherein the pump-gain integration optical fiber comprises an active fiber (31) positioned in the center and a pump fiber (32) positioned on the periphery of the active fiber, and the signal light part is used for outputting signal light to the active fiber of the pump-gain integration optical fiber (30); the pumping light part is used for coupling pumping light into a pumping fiber of the pumping-gain integrated optical fiber amplifier; the active fiber (31) is a multi-channel optical fiber, and the active fiber (31) comprises a doped fiber core positioned in the center, a low-refractive-index fiber ring region positioned on the periphery of the doped fiber core, a resonant ring region and a cladding.

2. The multi-ravine and pump-gain integration technique-based fiber laser amplifier of claim 1, wherein the active fiber (31) structure comprises a doped core f, a first low index fiber ring region e, a second low index fiber ring region c, a third low index fiber ring region a, a first resonant ring region d, a second resonant ring region b, and a cladding.

3. The fiber laser amplifier of claim 2, wherein the doped core f is located in the center of the active fiber, and a first low index fiber ring region e is disposed adjacent to and outside the active fiber, the first low index fiber ring region surrounding the doped core f; a first resonance ring area d is arranged on the outer side of the first low-refractive-index optical fiber ring area e in a close proximity mode, and the first resonance ring area d is close to and surrounds the first low-refractive-index optical fiber ring area e; a second low-refractive-index optical fiber ring area c is arranged on the outer side of the first resonance ring area d in a closely-adjacent mode, and the second low-refractive-index optical fiber ring area c is close to and surrounds the first resonance ring area d; a second resonance ring area b is arranged on the outer side of the second low-refractive-index optical fiber ring area c in an adjacent mode, and the second resonance ring area b is close to and surrounds the second low-refractive-index optical fiber ring area c; and a third low-refractive-index optical fiber ring area a is arranged on the outer side of the second resonance ring area b in a closely-adjacent mode, a quartz cladding is arranged on the outer side of the third low-refractive-index optical fiber ring area a in a closely-adjacent mode, and the quartz cladding is close to and surrounds the third low-refractive-index optical fiber ring area.

4. The fiber laser amplifier of claim 1, wherein the signal light portion comprises a single-mode output oscillator, the signal light is output through the single-mode output oscillator, the operating wavelength is the wavelength of the stimulated emission light of the rare-earth ions, the output fiber of the signal light portion and the active fiber of the pump-gain integrated fiber are low-insertion-loss fusion-spliced through the mode matcher, and the signal light is injected into the pump-gain integrated fiber amplifier to achieve signal light injection.

5. The fiber laser amplifier of claim 1, wherein the pump light output portions comprise two sets of pump light output portions, namely a first pump light output portion (1) and a second pump light output portion (2); the first pump light output section (1) corresponds to a forward input of the pump fiber of the pump gain integrated fiber, and the second pump light output section (2) corresponds to a reverse input of the pump fiber of the pump gain integrated fiber.

6. The optical fiber laser amplifier based on multiple-gully and pump-gain integration technology as claimed in claim 1, wherein the active fiber (31) is an 8-edge-shaped multi-gully fiber with cladding, 8 pump fibers are respectively bonded to 8 edges of the active fiber cladding, and the pump light can be coupled or guided from the pump fiber to the active fiber by evanescent wave coupling effect generated by bonding the pump fiber to the active fiber cladding.

7. The multi-ravine and pump-gain integration technique-based fiber laser amplifier of claim 1, wherein the active fiber (31) has a core doped with ytterbium ions, a total length of the active fiber is 15-35 m, a diameter of an f-region of the doped core is 25-50 μm, and a diameter of a cladding is 300-700 μm.

8. The fiber laser amplifier of claim 3, wherein the single-sided wall thickness of the first low-index fiber ring region is 1.5 μm to 2.5 μm, the single-sided wall thickness of the second low-index fiber ring region c is 1.5 μm to 2.5 μm, the single-sided wall thickness of the third low-index fiber ring region a is 1.5 μm to 2.5 μm, the first resonant ring region d is made of pure quartz, and the single-sided wall thickness is 6 μm to 10 μm; the second resonant ring region b is made of pure quartz, the thickness of a single-side wall is 6-10 μm, the diameter g =300-700 μm of the quartz cladding of the active fiber, and the diameter h of the pumping fiber in the pumping-gain integrated fiber is 200-360 μm.

9. The multi-gully and pump-gain integrated technology based fiber laser amplifier of claim 1, comprising a coiling region 40, wherein the coiling region 40 is a segment of the pump-gain integrated fiber that is bent and coiled for improving high order mode filtering effect of the active fiber multi-gully structure.

10. The pumping-gain integrated optical fiber is characterized by comprising an active fiber (31) positioned in the center and a pumping fiber (32) positioned at the periphery of the active fiber, wherein the active fiber (31) structurally comprises a doped fiber core f, a first low-refractive-index fiber ring area e, a second low-refractive-index fiber ring area c, a third low-refractive-index fiber ring area a, a first resonant ring area d, a second resonant ring area b and an external cladding, the doped fiber core f is positioned in the center of the active fiber, the first low-refractive-index fiber ring area e is arranged on the outer side of the doped fiber in a close proximity mode, and the first low-refractive-index fiber ring area is close to and surrounds the doped fiber core f; a first resonance ring area d is arranged on the outer side of the first low-refractive-index optical fiber ring area e in a close proximity mode, and the first resonance ring area d is close to and surrounds the first low-refractive-index optical fiber ring area e; a second low-refractive-index optical fiber ring area c is arranged on the outer side of the first resonant ring area d in an adjacent mode, and the second low-refractive-index optical fiber ring area c is close to and surrounds the first resonant ring area d; a second resonance ring area b is arranged on the outer side of the second low-refractive-index optical fiber ring area c in an adjacent mode, and the second resonance ring area b is close to and surrounds the second low-refractive-index optical fiber ring area c; a third low-refractive-index optical fiber ring area a is arranged on the outer side of the second resonance ring area b in an adjacent mode, a cladding is arranged on the outer side of the third low-refractive-index optical fiber ring area a in an adjacent mode, and the cladding is close to and surrounds the third low-refractive-index optical fiber ring area; the 8 pumping fibers are respectively attached to the cladding of the active fiber.

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