Reverse pumping high-power optical fiber amplifier

Abstract

The invention discloses a reverse pumping high-power optical fiber amplifier, which adopts a reverse pumping technology to realize optical fiber pumping and amplification under high power, and two dichroic mirrors are combined to form a simple isolator under signal light wavelength to prevent higher-power signal light from radiating into a pumping source to cause device damage. The mounting structures of the first lens and the second lens are designed, the correspondingly mounted first lens and second lens can be driven to perform X, Y, Z axis and pitching angle adjustment through the lens mounting assembly, and heat generated by a pumping surface is dispersed through the end cap, so that mode instability caused by a heat effect in the photonic crystal fiber is reduced; meanwhile, the clamping water-cooling assembly can clamp end caps of various sizes and conduct water-cooling temperature control on the end caps, in addition, the device is designed in a complete machine mode, the sealing performance is good, a free space light path in pump light is prevented from being affected by environmental factors, and adjustable combined installation of various lenses can be achieved through the device.

Description

Technical Field

[0001] The invention relates to the technical field of high-power optical fiber lasers, and in particular to a reverse-pumped high-power optical fiber amplifier. Background Art

[0002] With the continuous development of ultrafast laser performance in the past decade, the application prospects of high-energy, high-peak power femtosecond lasers in science, medicine and industry have received more and more attention, and the requirements for reliability, power, flexible repetition rate and price are getting higher and higher. Due to the excellent characteristics of optical fiber, such as cost-effectiveness, special compactness, high stability, especially ytterbium-doped fiber lasers, they have high optical pump efficiency and large gain bandwidth. By adopting chirped pulse amplification technology, the development of fiber lasers has made great progress. High-energy ultrafast femtosecond laser systems are in great demand in various fields such as high-precision industrial processing, clinical surgery and high harmonic generation.

[0003] However, due to the limitations of small mode field area and long transmission length, the pulse energy and peak power scale of ultrafast fiber lasers are severely limited by unnecessary nonlinear effects. In general, the threshold of nonlinear effects is proportional to the mode field diameter and inversely proportional to the length of the mode field. However, the increase in the fiber mode field diameter will lead to the emergence of higher-order modes, which will deteriorate the output beam quality. Therefore, the fiber mode field diameter cannot be arbitrarily increased to alleviate the nonlinear effect. In previous studies, large mode field fibers with specially designed thermal transistor structures have been developed to improve the pulse energy and peak power of ultrafast lasers, such as photonic crystal fibers, large spacing fibers, and chiral coupled core fibers. Among them, photonic crystal fibers are a technology with great application prospects. They can amplify ultrashort pulses to high average power and weaken the nonlinear accumulation during the amplification process. High-energy laser output requires high-power pump light input and high-gain main amplifier fiber. Compared with the traditional signal light and pump light co-coupling amplification through a fiber combiner, the reverse pumping technology can withstand beam powers of up to hundreds of watts, and studies have shown that the reverse pumping technology has a higher gain efficiency than the forward pumping technology. The reverse pumping technology is to focus the pump fiber into the cladding of the main amplifier fiber after it is collimated by a spatial optical system, so that the pump light achieves high gain efficiency through continuous oscillation in the cladding.

[0004] In order to obtain an output spot with a beam quality close to the diffraction limit, the traditional method is usually to fix the relative position of the fiber-coupled collimator and the subsequent optical path and not separate them, and connect them by fiber fusion splicing. The on-site processing, packaging and protection of the external melting point of the high-power optical fiber, thermal effect control and overall control of the pump optical system have become key factors in increasing the power of high-power lasers. However, this method has high requirements for on-site environmental pollution prevention, complex operation, low fault tolerance, and reliability is difficult to guarantee.

[0005] The existing reverse pumping high-power fiber lasers have the following problems: (1) The higher-power signal light generated by fiber coupling under high pump power will radiate into the semiconductor laser, causing device damage; (2) The thermal effect at the connection between the end cap and the amplifier stage fiber cannot be precisely controlled, resulting in mode instability; (3) Environmental factors in the free-space optical path, such as air dust, external vibration, noise, and pump waste heat, which lead to low pump efficiency and unstable output beam; (4) When it is necessary to replace a different lens coupling combination, the lens combination cannot be uniformly collimated using the same device. When changing the focal length lens combination, the device must be changed accordingly. Summary of the invention

[0006] In order to solve the problems existing in the above-mentioned background technology, the present invention provides a reverse-pumped high-power fiber amplifier, which adopts reverse pumping technology to realize fiber pumping and amplification at high power, prevents high-power signal light from radiating into the pump source-semiconductor laser, causing device damage, and realizes cooling and temperature control of the connection between the end cap and the amplifier-stage optical fiber. The device adopts an integrated design with good sealing performance, avoids the free space optical path in the pump light from being affected by environmental factors, integrates the reverse pumping module with the fiber laser output, realizes synchronous input and output, and the device is convenient and adjustable (can realize adjustable combination installation of multiple lenses), safe and reliable, and easy to adjust.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: The present invention provides a reverse pumped high-power optical fiber amplifier, comprising an outer shell, a pump source, a seed source, a spatial light collimation and focusing component, an end cap, a clamping water cooling component and an amplifying optical fiber; The spatial light collimating and focusing assembly and the clamping water cooling assembly are both installed inside the outer shell, the spatial light collimating and focusing assembly includes a first lens, a first dichroic mirror, a second dichroic mirror and a second lens arranged in sequence, the amplifying stage optical fiber is arranged opposite to the second lens, and the end cap is installed at one end of the second amplifying stage optical fiber close to the second lens, the clamping water cooling assembly is fixedly installed inside the outer shell, and the end cap is clamped, fixed and cooled; The signal light output by the seed source enters the amplifying optical fiber in the forward direction, the pump light output by the pump source enters the interior of the outer shell through the pump output optical fiber, is collimated by the first lens, and then is focused by the second lens after passing through the first dichroic mirror and the second dichroic mirror, and then enters the amplifying optical fiber in the reverse direction after passing through the end cap, the amplifying optical fiber couples and amplifies the received pump light and signal light and outputs the amplified signal light in the forward direction, and the amplified signal light is collimated by the second lens, and then is reflected and output by the first dichroic mirror and the second dichroic mirror.

[0008] Specifically, a signal output fiber for transmitting signal light is connected between the seed source and the amplifier-level optical fiber. The amplifier-level optical fiber includes photonic crystal fiber, large mode field double-clad fiber, single crystal fiber, etc., which can be selected according to different signal light wavelengths. The seed source can be specifically selected from fiber lasers of different wavelength bands, including but not limited to ytterbium-doped 1030nm seed sources, erbium-doped 1550nm lasers, etc. In this system, fiber lasers or semiconductor lasers are used, and the wavelength of the signal light output by the seed source is compatible with the amplifier-level optical fiber.

[0009] The output end of the pump source is connected to a pump output optical fiber for transmitting pump light. In a specific embodiment, a semiconductor laser is used as a pump light source, and its output power is as high as 400W. Reverse pumping (forward refers to the direction of transmission of signal light emitted by the seed source) is combined with a spatial light collimation and focusing component to collimate and focus the pump light beam so that it is incident into the cladding of the amplifier-stage optical fiber with an optimal spot size and a suitable numerical aperture.

[0010] Reverse pumping is to output the pump light as spatial light, use a combination of spatial lenses to collimate and focus it, and finally couple it into the inner cladding of the amplifying optical fiber. Since the diameter of the inner cladding is several times that of the fiber core, the coupling efficiency of the pump light can be increased by dozens of times, which can reduce the loss of pump light during optical fiber coupling and improve the pulse amplification efficiency. At the same time, most of the pump light is absorbed and consumed, reducing the heat radiation of the residual light.

[0011] The working principle of the reverse pumped high power fiber amplifier in the present invention is as follows: The signal light output by the seed source is transmitted through the signal output optical fiber and enters the amplifying optical fiber in the forward direction. The pump light output by the pump source enters the outer shell through the pump output optical fiber. The pump light is collimated by the first lens, and then focused by the second lens after passing through the first dichroic mirror and the second dichroic mirror. Then, it is reversely input into the amplifying optical fiber after passing through the end cap. The amplifying optical fiber couples and amplifies the received pump light and signal light and outputs the amplified signal light in the forward direction (the forward direction refers to the transmission direction of the signal light emitted by the seed source). After the amplified signal light is collimated by the second lens, it is reflected and output by the first dichroic mirror and the second dichroic mirror.

[0012] For high-power signal light output, if only one dichroic mirror is set, the dichroic mirror is a dichroic mirror (a reflector with two coated surfaces), and the coating characteristics are high transmittance to pump light and high reflection to signal light. However, the current coating accuracy cannot reach 100% reflectivity to signal light. For example, the coating accuracy is 98% reflectivity to signal light, and 2% of signal light passes through the reflector. In this case, when the output power is 100W, nearly 2W of light will enter the pump source-semiconductor laser, causing device damage. In order to solve the isolation problem of high signal light output in fiber coupling under high pump power, the present invention forms a simplified isolator under the signal light wavelength by combining two dichroic mirrors to prevent high signal light from radiating into the pump source-semiconductor laser, causing device damage.

[0013] In addition, in order to solve the problem of the power per unit area of ​​the pump light receiving surface under high-power pumping, the heat generated by the pump surface is dispersed through the end cap to reduce the mode instability caused by the thermal effect in the photonic crystal fiber. At the same time, the clamping water cooling component can clamp end caps of various sizes and perform water cooling and temperature control on them.

[0014] In order to prevent the free space optical path in the reverse pumping space pump light from being affected by external environmental factors, the closed overall design can avoid the influence of external vibration, noise and excess pump light waste heat, integrate the reverse pump module with the fiber laser output, realize synchronous input and output, realize high-power laser pump light collimation and coupling, and collimation of the amplified signal light, and the device is convenient and adjustable (various lenses can be installed in an adjustable combination), safe and reliable, and easy to adjust.

[0015] Furthermore, the mounting structures of the first lens and the second lens are the same, and they are both mounted inside the outer shell through a lens mounting assembly, and the lens mounting assembly includes a lens barrel, a holder, a lens frame, a transverse mounting seat and a vertical mounting seat; a lens is mounted inside the lens barrel, and the lens frame is an L-shaped structure, a mounting hole is provided on the transverse part of the lens frame, the holder is installed in the mounting hole, and the lens barrel is installed on the holder in the mounting hole, and the position of the lens barrel along the X-axis direction can be adjusted by rotating the lens barrel; one or more first waist-shaped adjustment grooves are provided on the vertical mounting seat along the length direction, and the vertical part of the lens frame is correspondingly mounted on the vertical mounting seat by means of a locking bolt and a nut; the transverse mounting seat is installed on one end of the vertical mounting seat, and the transverse mounting seat is provided with one or more second waist-shaped adjustment grooves along the X-axis direction, and the transverse mounting seat is mounted on the outer shell by means of a locking bolt and a nut.

[0016] In the present invention, in order to solve the isolation problem of high signal light output in fiber coupling under high pump power, two dichroic mirrors are combined to form a simplified isolator at the signal light wavelength to prevent high signal light from radiating into the pump source - semiconductor laser, causing device damage.

[0017] However, in actual application, the inventors found that there will be an optical path difference between the two lenses due to passing through two dichroic mirrors. The X-axis position (position in the optical axis direction) of the first lens and the second lens needs to be adjusted accordingly based on the optical path difference calculated according to the actual dichroic mirror lens thickness. In addition, when using optical fibers with different pump lights and optical fibers with different amplification levels, the different core diameters will lead to different lens combinations, and the installation position of the lens also needs to be changed. The lens installation structure in the prior art is a welded fixed type, which is not convenient for adjusting the installation position of the lens. The lens combination cannot be uniformly collimated using the same device. If the focal length lens combination is changed, the device must be changed.

[0018] In the present invention, the mounting structure of the first lens and the second lens is designed. Specifically, a lens mounting assembly is used as a five-dimensional adjustable frame, that is, the lens mounting assembly can drive the correspondingly installed first lens and second lens to perform X, Y, Z axis and pitch angle adjustment. The lens mounting assembly adopts the cooperation of a lens frame, a transverse mounting seat and a vertical mounting seat. The vertical part of the L-shaped lens frame cooperates with the first waist-shaped adjustment groove and the locking bolt on the vertical mounting seat to realize the adjustment of the lens in the Z-axis direction (the adjustment range is within 10mm). The second waist-shaped adjustment groove and the locking bolt on the transverse mounting seat cooperate to realize the adjustment of the lens in the X-axis direction (the adjustment range is within 10mm). By cooperating with the holder and the lens barrel, the lens barrel can be rotated to perform micron-level distance fine-tuning of the position of the lens along the X-axis direction (optical axis direction). It is suitable for most common thickness reflector lenses on the market (the thickness can be 2-10mm). During installation, the pitch angle of the lens can be adjusted by rotating the lens frame. In addition, the lens frame is equipped with Y-axis and Z-axis fine-tuning knobs. By manipulating the corresponding fine-tuning knobs, the position of the lens in the Y-axis and Z-axis directions can be fine-tuned.

[0019] Furthermore, the clamping water cooling assembly includes a base, a clamping lower seat and a clamping upper seat; the base is installed inside the outer shell, the clamping lower seat can be detachably installed on the base, and the clamping upper seat can be detachably installed on the top of the clamping lower seat, and the bottom of the clamping upper seat and the top of the clamping lower seat are both provided with V-shaped clamping grooves that cooperate with the outer side of the end cap for clamping and fixing, the clamping lower seat and the clamping upper seat are both made of copper, and cooling channels are provided inside the clamping lower seat and the clamping upper seat.

[0020] Two copper blocks with V-shaped clamping grooves are used together. The upper clamping seat and the lower clamping seat are connected to each other with a square through hole of a certain length in the middle, which can firmly fix the cylindrical part of the end cap. A cooling channel is formed inside the upper clamping seat and the lower clamping seat for cooling, cooling and temperature control of the end cap to reduce the heat of the high-energy pump and output fiber connector. Moreover, the upper clamping seat and the lower clamping seat are both detachable, and can be replaced with a matching upper clamping seat and a lower clamping seat according to a specific size of the end cap (the size of the end cap is adjusted according to the applicability of the lens combination), and the device has stronger applicability.

[0021] Furthermore, U-shaped grooves are provided at the upper parts of the front and rear sides of the clamping lower seat, and the bottom of the U-shaped groove is mounted with the base through fastening bolts. The front and rear sides of the bottom of the clamping upper seat are respectively provided with lateral extension ends, which respectively cooperate with the upper ends of the two side arms of the U-shaped groove and are fixedly installed by fastening bolts.

[0022] Through the above structural adjustment, the structures of the clamping lower seat and the clamping upper seat are more compact, and the clamping lower seat and the clamping upper seat are tightly docked and fixed, ensuring the clamping and fixing effect of the end cap.

[0023] Furthermore, a first cooling channel is formed inside the clamping lower seat, and a second cooling channel is formed inside the clamping upper seat. When the clamping lower seat and the clamping upper seat are installed correspondingly, the ports of the first cooling channel and the second cooling channel are connected to form a flow channel. Elastic sealing gaskets are provided at the ports of the first cooling channel and the second cooling channel, and one end of the elastic sealing gasket extends out of the corresponding docking surfaces of the clamping lower seat and the clamping upper seat.

[0024] By providing elastic sealing gaskets at the ports of the first cooling channel and the second cooling channel, and extending one end of the elastic sealing gasket out of the corresponding docking surfaces of the clamping lower seat and the clamping upper seat, in addition, when the clamping upper seat and the clamping lower seat are docked and fixed, the four corners are locked downward by fastening bolts, thereby ensuring the sealing of the docking point between the first cooling channel inside the clamping lower seat and the second cooling channel port inside the clamping upper seat.

[0025] Specifically, two water-cooling pipe joints are located on the same surface of the clamping upper seat and the clamping lower seat. The two water-cooling pipe joints are respectively connected to two water pipes (a water inlet pipe and a water outlet pipe). The two water pipes are output through the same water-cooling outlet on the outer shell. A sealing rubber ring is provided at the water-cooling outlet for use with the two water pipes to facilitate the sealing of the entire machine.

[0026] Furthermore, a side water cooling pipe is provided on the side of the outer shell, and an external water cooler is connected to achieve precise temperature control inside the reverse high-power pump machine.

[0027] Furthermore, the outer shell is provided with two amplified light output ports (respectively a first amplified light output port and a second amplified light output port), which respectively cooperate with the first dichroic mirror and the second dichroic mirror to reflect and output the amplified signal light. The two amplified light output ports are installed with optical window pieces, and the first amplified light output port cooperating with the first dichroic mirror serves as a detection port for performing real-time power stability detection on the amplified signal light.

[0028] Since the first dichroic mirror and the second dichroic mirror are dichroic mirrors, the coating characteristics are high transmittance to pump light and high reflection to signal light. However, the current coating accuracy cannot achieve 100% reflectivity to signal light. Therefore, most of the amplified signal light is reflected by the second dichroic mirror and then output from the second amplified light output port, which serves as the main output port; a small part of the amplified signal light is reflected by the first dichroic mirror and then output from the first amplified light output port. The amplified signal light reflected and output from the first amplified light output port is very small, which serves as a detection port, realizing real-time detection of the power stability of the amplified signal light, ensuring that the output performance of the amplifier meets expectations, and ensuring the stability and reliability of the laser system.

[0029] Furthermore, the end cap is made of quartz material, and includes a cylindrical end cap body. The outer surface of the end cap body is coated with a dielectric film to resist the signal light wavelength and the pump light wavelength. A guide rod is coaxially provided at one end of the end cap body, and a tapered connecting portion is formed between the end cap body and the guide rod. The end of the amplification stage optical fiber is installed in the guide rod, and the V-shaped clamping groove is in contact with the outer side of the end cap body.

[0030] Furthermore, the first dichroic mirror and the second dichroic mirror are compactly mounted inside the outer shell through a dichroic mirror frame, and the first dichroic mirror and the second dichroic mirror are mounted at an inclination angle of 45 degrees. In specific applications, the inclination direction of the dichroic mirror can be adjusted and set according to the output direction of the signal light, and the dichroic mirror frames will not block the output of the amplified signal light. The first dichroic mirror and the second dichroic mirror are both dichroic mirrors coated on both sides, and a high-transmittance film for transmitting the pump light collimated by the first lens is provided on the side of the dichroic mirror close to the first lens, and a high-reflection film for reflecting the signal light amplified by the amplifier-stage optical fiber coupling is provided on the side of the dichroic mirror close to the second lens.

[0031] Furthermore, the first lens and the second lens are plano-convex lenses, the opposite side of the first lens and the second lens is a focusing mirror, and the opposite side of the first lens and the second lens is a collimating mirror.

[0032] Specifically, the pump light is collimated by the first lens, and then passes through the first dichroic mirror and the second dichroic mirror to be focused by the second lens, and then passes through the end cap to enter the amplifying optical fiber in the reverse direction. The amplifying optical fiber couples and amplifies the received pump light and signal light and outputs the amplified signal light forward. The amplified signal light is collimated by the second lens, and then reflected by the first dichroic mirror and the second dichroic mirror, and finally output from the second amplified light output port and the first amplified light output port.

[0033] Compared with the prior art, the present invention has the following beneficial effects: (1) In order to solve the isolation problem of high signal light output in fiber coupling under high pump power, the present invention forms a simplified isolator at the signal light wavelength by combining two dichroic mirrors to prevent high signal light from radiating into the pump source - semiconductor laser, causing device damage.

[0034] (2) In order to solve the problem that the lens combination cannot be uniformly collimated with the same device, and the device must be changed when changing the focal length lens combination, the present invention designs the mounting structure of the first lens and the second lens. Specifically, the lens mounting assembly is used as a five-dimensional adjustable frame. That is, the lens mounting assembly can drive the corresponding first lens and the second lens to be adjusted in the X, Y, Z axis and pitch angle. The lens mounting assembly uses a lens frame, a horizontal mounting seat and a vertical mounting seat to cooperate. The vertical part of the L-shaped lens frame cooperates with the first waist-shaped adjustment groove and the locking bolt on the vertical mounting seat to achieve the adjustment of the lens in the Z-axis direction (adjustment). The adjustment range is within 10mm), and the lens can be adjusted in the X-axis direction (the adjustment range is within 10mm) by cooperating with the second waist-shaped adjustment groove and the locking bolt on the lateral mounting seat. By cooperating with the holder and the lens barrel, the position of the lens along the X-axis direction (optical axis direction) can be fine-tuned at the micron level by rotating the lens barrel. It is suitable for most reflector lenses with common thickness on the market (the thickness can be 2-10mm). The pitch angle of the lens can be adjusted by rotating the lens frame during installation. In addition, the Y-axis and Z-axis fine-tuning knobs are installed on the lens frame. The position of the lens in the Y-axis and Z-axis directions can be fine-tuned by operating the corresponding fine-tuning knobs.

[0035] (3) In order to solve the problem of the power per unit area of ​​the pump light receiving surface under high-power pumping, the heat generated by the pump surface is dispersed through the end cap to reduce the mode instability caused by the thermal effect in the photonic crystal fiber. At the same time, the clamping water cooling component can clamp end caps of various sizes and perform water cooling and temperature control on them.

[0036] (4) In order to prevent the free space optical path in the reverse pumping space pumping light from being affected by external environmental factors, the closed overall design can avoid the influence of external vibration, noise and excess pumping light waste heat, integrate the reverse pumping module with the fiber laser output, realize synchronous input and output, realize high-power laser pumping light collimation and coupling, and collimate the signal light after amplification. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] Figure 1 Schematic diagram of the external structure of the reverse-pumped high-power optical fiber amplifier of the present invention; Figure 2 A schematic diagram of the internal structure of the reversely pumped high-power optical fiber amplifier of the present invention; Figure 3 It is a three-dimensional diagram of the lens mounting assembly in the present invention; Figure 4 A three-dimensional diagram of the lens mounting assembly of the present invention from another perspective; Figure 5 A three-dimensional diagram of the clamping position of the water cooling component in the present invention; Figure 6 A cross-sectional view of a location where a water cooling component is clamped in the present invention; Figure 7 A three-dimensional diagram of the clamping lower seat in the present invention; Figure 8 Schematic diagram of the structure of the end cap in the present invention; Fig. 9 This is a working principle diagram of the reverse-pumped high-power optical fiber amplifier of the present invention; Fig.10 This is a light path diagram of the reverse-pumped high-power optical fiber amplifier of the present invention when it is working.

[0039] Among them, the specific drawings are marked as: Outer shell 1, water cooling outlet 2, first magnified light output port 3, second magnified light output port 4, first lens 5, first dichroic mirror 6, second dichroic mirror 7, second lens 8, dichroic mirror frame 9, lens mounting assembly 10, lens barrel 11, fine-tuning knob 12, lens frame 13, vertical mounting seat 14, first waist-shaped adjustment groove 15, horizontal mounting seat 16, second waist-shaped adjustment groove 17, end cap 18, end cap body 19, tapered connecting part 20, guide rod 21, magnifying optical fiber 22, clamping water cooling assembly 23, base 24, clamping lower seat 25, U-shaped groove 26, first cooling channel 27, clamping upper seat 28, horizontal extension end 29, second cooling channel 30, elastic sealing gasket 31, V-shaped clamping groove 32, water cooling pipe joint 33, water pipe 34. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] The embodiment of the present invention discloses a reverse pumped high power optical fiber amplifier, such as Figure 1 , Figure 2 , Fig. 9 and Fig.10 As shown, it includes an outer shell 1, a pump source, a seed source, a spatial light collimation and focusing component, an end cap 18, a clamping water cooling component 23 and an amplification-stage optical fiber 22; The outer shell 1 is a rectangular structure formed by a top plate, a bottom plate and four side plates. The spatial light collimation and focusing assembly and the clamping water cooling assembly 23 are both installed on the bottom plate. The spatial light collimation and focusing assembly includes a first lens 5, a first dichroic mirror 6, a second dichroic mirror 7 and a second lens 8 which are arranged in sequence. The amplifying optical fiber 22 is arranged opposite to the second lens 8. An end cap 18 is installed at one end of the second amplifying optical fiber 22 close to the second lens 8. The clamping water cooling assembly 23 is fixedly installed on the bottom plate, and the end cap 18 is clamped, fixed and cooled. The signal light output by the seed source enters the amplifier-stage optical fiber 22 in the forward direction, and the pump light output by the pump source enters the interior of the outer shell 1 through the pump output optical fiber, is collimated by the first lens 5, and then is focused by the second lens 8 after passing through the first dichroic mirror 6 and the second dichroic mirror 7, and then enters the amplifier-stage optical fiber 22 in the reverse direction after passing through the end cap 18. The amplifier-stage optical fiber 22 couples and amplifies the received pump light and signal light and outputs the amplified signal light in the forward direction. The amplified signal light is collimated by the second lens 8, and then reflected and output by the second dichroic mirror 7 and the first dichroic mirror 6.

[0042] Specifically, a signal output fiber for transmitting signal light is connected between the seed source and the amplifier-level optical fiber 22. The amplifier-level optical fiber 22 includes photonic crystal fiber, large mode field double-clad fiber, single crystal fiber, etc., which can be selected according to different signal light wavelengths. The seed source can be specifically selected to use fiber lasers of different bands for input, including but not limited to ytterbium-doped 1030nm seed sources, erbium-doped 1550nm lasers, etc. In this system, fiber lasers or semiconductor lasers are used, and the wavelength of the signal light output by the seed source is compatible with the amplifier-level optical fiber 22.

[0043] The output end of the pump source is connected to a pump output optical fiber for transmitting pump light. In a specific embodiment, a semiconductor laser is used as a pump light source, and its output power is as high as 400W. Reverse pumping (forward refers to the direction of transmission of the signal light emitted by the seed source) is combined with a spatial light collimation and focusing component to collimate and focus the pump light beam so that it is incident into the cladding of the amplifier-stage optical fiber 22 with an optimal spot size and a suitable numerical aperture.

[0044] Reverse pumping is to output the pump light as spatial light, collimate and focus it using a combination of spatial lenses, and finally couple it into the inner cladding of the amplifying optical fiber 22. Since the diameter of the inner cladding is several times that of the core, the coupling efficiency of the pump light can be increased by dozens of times, which can reduce the loss of pump light during optical fiber coupling and improve the pulse amplification efficiency. At the same time, most of the pump light is absorbed and consumed, reducing the heat radiation of the residual light.

[0045] The working principle of the reverse pumped high power fiber amplifier in the present invention is as follows: The signal light output by the seed source is transmitted through the signal output optical fiber and enters the amplifier-stage optical fiber 22 in the forward direction. The pump light output by the pump source enters the outer shell 1 through the pump output optical fiber. The pump light is collimated by the first lens 5, and then focused by the second lens 8 after passing through the first dichroic mirror 6 and the second dichroic mirror 7. Then, it is reversely input into the amplifier-stage optical fiber 22 after passing through the end cap 18. The amplifier-stage optical fiber 22 couples and amplifies the received pump light and signal light and outputs the amplified signal light in the forward direction (the forward direction refers to the transmission direction of the signal light emitted by the seed source). After the amplified signal light is collimated by the second lens 8, it is reflected and output by the first dichroic mirror 6 and the second dichroic mirror 7.

[0046] For high-power signal light output, if only one dichroic mirror is set, the dichroic mirror is a dichroic mirror (a reflector with two coated surfaces), and the coating characteristics are high transmittance to pump light and high reflection to signal light. However, the current coating accuracy cannot reach 100% reflectivity to signal light. For example, the coating accuracy is 98% reflectivity to signal light, and 2% of signal light passes through the reflector. In this case, when the output power is 100W, nearly 2W of light will enter the pump source-semiconductor laser, causing device damage. In order to solve the isolation problem of high signal light output in fiber coupling under high pump power, the present invention forms a simplified isolator under the signal light wavelength by combining two dichroic mirrors to prevent high signal light from radiating into the pump source-semiconductor laser, causing device damage.

[0047] In addition, in order to solve the problem of the power per unit area of ​​the pump light receiving surface under high-power pumping, the heat generated by the pump surface is dispersed through the end cap 18 to reduce the mode instability caused by the thermal effect in the photonic crystal fiber. At the same time, the clamping water cooling component 23 can clamp end caps 18 of various sizes and perform water cooling and temperature control on them.

[0048] In order to prevent the free space optical path in the reverse pumping space pump light from being affected by external environmental factors, the closed overall design can avoid the influence of external vibration, noise and excess pump light waste heat, integrate the reverse pump module with the fiber laser output, realize synchronous input and output, realize high-power laser pump light collimation and coupling, and collimation of the amplified signal light, and the device is convenient and adjustable (various lenses can be installed in an adjustable combination), safe and reliable, and easy to adjust.

[0049] like Figure 3 and Figure 4 As shown, in the specific embodiment, the mounting structures of the first lens 5 and the second lens 8 are the same, and they are both mounted on the bottom plate through a lens mounting assembly 10, and the lens mounting assembly 10 includes a lens barrel 11, a holder, a lens frame 13, a horizontal mounting seat 16 and a vertical mounting seat 14; a lens is mounted inside the lens barrel 11, and the lens frame 13 is an L-shaped structure, and a mounting hole is opened on the horizontal part of the lens frame 13, and the holder is coaxially mounted in the mounting hole, and the lens barrel 11 is mounted in the mounting hole and is rotatably mounted with the holder, and the lens barrel 11 is rotated. 1 can adjust the position of the lens barrel 11 along the X-axis direction; the vertical mounting seat 14 is provided with one or more first waist-shaped adjustment grooves 15 along the length direction, and the vertical portion of the lens frame 13 is correspondingly mounted with the vertical mounting seat 14 by means of locking bolts and nuts; a transverse mounting seat 16 is vertically mounted at one end of the vertical mounting seat 14, and the transverse mounting seat 16 is provided with one or more second waist-shaped adjustment grooves 17 along the X-axis direction, and the transverse mounting seat 16 is mounted on the outer shell 1 by means of locking bolts and nuts.

[0050] In the present invention, in order to solve the isolation problem of high signal light output in fiber coupling under high pump power, two dichroic mirrors are combined to form a simplified isolator at the signal light wavelength to prevent high signal light from radiating into the pump source - semiconductor laser, causing device damage.

[0051] However, in actual application, the inventors found that there is an optical path difference between the two lenses due to the two dichroic mirrors. The X-axis position (optical axis position) of the first lens 5 and the second lens 8 needs to be adjusted accordingly based on the optical path difference calculated according to the actual dichroic mirror lens thickness (e.g. Fig.10 As shown). In addition, when using optical fibers with different pump lights and optical fibers 22 with different amplification levels, the different core diameters will lead to different lens combinations, and the installation position of the lens also needs to be changed. The lens installation structure in the prior art is a welding fixed type, which is not convenient for adjusting the installation position of the lens. The lens combination cannot be uniformly collimated using the same device. If the focal length lens combination is changed, the device must be changed.

[0052] In the present invention, the mounting structure of the first lens 5 and the second lens 8 is designed. Specifically, a lens mounting assembly 10 is used as a five-dimensional adjustable frame. That is, the lens mounting assembly 10 can drive the correspondingly installed first lens 5 and second lens 8 to perform X, Y, Z axis and pitch angle adjustment. The lens mounting assembly 10 adopts a lens frame 13, a horizontal mounting seat 16 and a vertical mounting seat 14. The vertical portion of the L-shaped lens frame 13 cooperates with the first waist-shaped adjustment groove 15 and the locking bolt on the vertical mounting seat 14 to achieve the adjustment of the lens in the Z-axis direction (the adjustment range is within 10 mm). The second waist-shaped adjustment groove 17 on the horizontal mounting seat 16 cooperates with the locking bolt to achieve the adjustment of the lens in the X-axis direction (the adjustment range is within 10 mm). By cooperating with the holder and the lens barrel 11, the lens barrel 11 can be rotated to fine-tune the position of the lens along the X-axis direction (optical axis direction) at the micron level. It is suitable for most common reflector lenses of common thickness on the market (the thickness can be 2-10 mm). During installation, the pitch angle of the lens can be adjusted by rotating the lens frame 13. In addition, the lens frame 13 is equipped with Y-axis and Z-axis fine-tuning knobs 12. By manipulating the corresponding fine-tuning knobs 12, the position of the lens in the Y-axis and Z-axis directions can be fine-tuned.

[0053] like Figures 5 to 7 As shown, in a specific embodiment, the clamping water cooling assembly 23 includes a base 24, a clamping lower seat 25 and a clamping upper seat 28; the base 24 is installed on the bottom plate, the clamping lower seat 25 is detachably installed on the base 24, and the clamping upper seat 28 is detachably installed on the top of the clamping lower seat 25, and the bottom of the clamping upper seat 28 and the top of the clamping lower seat 25 are both provided with V-shaped clamping grooves 32 that cooperate with the outer side of the end cap 18 for clamping and fixing, the clamping lower seat 25 and the clamping upper seat 28 are both made of copper, and cooling channels are provided inside the clamping lower seat 25 and the clamping upper seat 28. Two copper blocks with V-shaped clamping grooves 32 are used together. The clamping upper seat 28 and the clamping lower seat 25 are connected to a square through hole with a certain length in the middle, which can firmly fix the cylindrical part of the end cap 18. A cooling channel is formed inside the clamping upper seat 28 and the clamping lower seat 25 for cooling, cooling and temperature control of the end cap 18 to reduce the heat of the high-energy pump and output fiber connector. Moreover, the clamping upper seat 28 and the clamping lower seat 25 are both detachable. The clamping upper seat 28 and the clamping lower seat 25 can be replaced with a matching clamping upper seat 28 and a clamping lower seat 25 according to a specific size of the end cap 18 (the size of the end cap 18 is adjusted according to the applicability of the lens combination), and the device has stronger applicability.

[0054] In the specific embodiment, U-shaped grooves 26 are provided at the upper parts of the front and rear sides of the clamping lower seat 25, and the bottom of the U-shaped groove 26 is mounted with the base 24 by fastening bolts, and the front and rear sides of the bottom of the clamping upper seat 28 are respectively provided with transverse extension ends 29, which are respectively matched with the upper ends of the two side arms of the U-shaped groove and fixedly installed by fastening bolts. Through the above structural adjustment, the compactness of the structure of the clamping lower seat 25 and the clamping upper seat 28 is better, and the clamping lower seat 25 and the clamping upper seat 28 are closely docked and fixed, ensuring the clamping and fixing effect of the end cap 18.

[0055] Preferably, a first cooling channel 27 is formed inside the clamping lower seat 25, and a second cooling channel 30 is formed inside the clamping upper seat 28. The first cooling channel 27 and the second cooling channel 30 are water channels. When the clamping lower seat 25 and the clamping upper seat 28 are installed correspondingly, the ports of the first cooling channel 27 and the second cooling channel 30 are connected to form a flow channel. Elastic sealing gaskets 31 are provided at the ports of the first cooling channel 27 and the second cooling channel 30, and one end of the elastic sealing gasket 31 extends out of the corresponding docking surfaces of the clamping lower seat 25 and the clamping upper seat 28. By providing elastic sealing gaskets 31 at the ports of the first cooling channel 27 and the second cooling channel 30, and extending one end of the elastic sealing gasket 31 out of the corresponding docking surfaces of the clamping lower seat 25 and the clamping upper seat 28, in addition, when the clamping upper seat 28 and the clamping lower seat 25 are docked and fixed, the four corners are locked downward by fastening bolts, thereby ensuring the sealing of the docking point between the first cooling channel 27 inside the clamping lower seat 25 and the second cooling channel 30 inside the clamping upper seat 28.

[0056] Specifically, the two water-cooling pipe joints 33 are located on the same surface of the clamping upper seat 28 and the clamping lower seat 25. One ends of the two water-cooling pipe joints 33 are respectively connected to the first cooling channel 27 and the second cooling channel 30, and the other ends are respectively connected to two water pipes 34 (respectively, a water inlet pipe and a water outlet pipe). The two water pipes 34 are output through the same water-cooling outlet 2 on the outer shell 1. A sealing rubber ring used in conjunction with the two water pipes 34 is provided at the water-cooling outlet 2 to facilitate the sealing of the entire machine.

[0057] In a specific embodiment, a side water cooling pipe is provided on the side of the outer shell 1, and an external water cooler is connected to achieve precise temperature control inside the reverse high-power pump machine.

[0058] In a specific embodiment, two amplified light output ports (respectively a first amplified light output port 3 and a second amplified light output port 4) are provided on the outer shell 1, which are respectively cooperated with the first dichroic mirror 6 and the second dichroic mirror 7 to reflect and output the amplified signal light. Optical windows are installed at the two amplified light output ports, and the first amplified light output port 3 cooperated with the first dichroic mirror 6 is used as a detection port for performing real-time power stability detection on the amplified signal light. Since the first dichroic mirror 6 and the second dichroic mirror 7 are dichroic mirrors, the coating characteristics are high transmittance to the pump light and high reflection to the signal light. However, the current coating accuracy cannot reach 100% reflectivity to the signal light. Therefore, most of the amplified signal light is reflected by the second dichroic mirror 7 and then output from the second amplified light output port 4, which is used as the main output port here; a small part of the amplified signal light is reflected by the first dichroic mirror 6 and then output from the first amplified light output port 3. The amplified signal light reflected and output from the first amplified light output port 3 is very small, which is used as a detection port here, thereby realizing real-time detection of the power stability of the amplified signal light, ensuring that the output performance of the amplifier meets expectations, and ensuring the stability and reliability of the laser system.

[0059] like Figure 8 As shown, in a specific embodiment, the end cap 18 is made of quartz material, and the end cap 18 includes a cylindrical end cap body 19. The outer surface of the end cap body 19 is coated with a dielectric film to resist the signal light wavelength and the pump light wavelength. A guide rod 21 is coaxially provided at one end of the end cap body 19, and a tapered connecting portion 20 is formed between the end cap body 19 and the guide rod 21. The end of the amplification stage optical fiber 22 is installed in the guide rod 21, and the V-shaped clamping groove 32 is in contact with the outer side of the end cap body 19.

[0060] In a specific embodiment, the first dichroic mirror 6 and the second dichroic mirror 7 are compactly installed inside the outer shell 1 through the dichroic mirror frame 9. The first dichroic mirror 6 and the second dichroic mirror 7 are installed with an inclination angle of 45 degrees. In specific applications, the inclination direction of the dichroic mirror can be adjusted and set according to the output direction of the signal light, and the dichroic mirror frames 9 will not block the output of the amplified signal light. The first dichroic mirror 6 and the second dichroic mirror 7 are both dichroic mirrors coated on both sides. The side of the dichroic mirror close to the first lens 5 is provided with a high-transmittance film that transmits the pump light collimated by the first lens 5, and the side of the dichroic mirror close to the second lens 8 is provided with a high-reflection film for reflecting the signal light amplified by the coupling of the amplifier-stage optical fiber 22.

[0061] In a specific embodiment, the first lens 5 and the second lens 8 are plano-convex lenses, the opposite side of the first lens 5 and the second lens 8 is a focusing mirror, and the opposite side of the first lens 5 and the second lens 8 is a collimating mirror. Specifically, after the pump light is collimated by the first lens 5, it is focused by the second lens 8 after passing through the first dichroic mirror 6 and the second dichroic mirror 7, and then enters the amplifier-level optical fiber 22 in the reverse direction after passing through the end cap 18. The amplifier-level optical fiber 22 couples and amplifies the received pump light and signal light and outputs the amplified signal light in the forward direction. After the amplified signal light is collimated by the second lens 8, it is reflected by the first dichroic mirror 6 and the second dichroic mirror 7, and finally outputs from the second amplified light output port 4 and the first amplified light output port 3.

[0062] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A reverse-pumped high-power optical fiber amplifier, characterized in that: It includes an outer shell, a pump source, a seed source, a spatial light collimation and focusing component, an end cap, a clamping water cooling component and an amplification-level optical fiber; The spatial light collimating and focusing assembly and the clamping water cooling assembly are both installed inside the outer shell, the spatial light collimating and focusing assembly includes a first lens, a first dichroic mirror, a second dichroic mirror and a second lens arranged in sequence, the amplifying stage optical fiber is arranged opposite to the second lens, and the end cap is installed at one end of the second amplifying stage optical fiber close to the second lens, the clamping water cooling assembly is fixedly installed inside the outer shell, and the end cap is clamped, fixed and cooled; The signal light output by the seed source enters the amplifying optical fiber in the forward direction, the pump light output by the pump source enters the interior of the outer shell through the output optical fiber, is collimated by the first lens, and then is focused by the second lens after passing through the first dichroic mirror and the second dichroic mirror, and then enters the amplifying optical fiber in the reverse direction after passing through the end cap, the amplifying optical fiber couples and amplifies the received pump light and signal light and outputs the amplified signal light in the forward direction, and the amplified signal light is collimated by the second lens, and then is reflected and output by the first dichroic mirror and the second dichroic mirror.

2. The reverse-pumped high-power optical fiber amplifier according to claim 1, characterized in that: The mounting structures of the first lens and the second lens are the same, and both are mounted inside the outer shell through a lens mounting assembly, and the lens mounting assembly includes a lens barrel, a holder, a lens frame, a transverse mounting seat and a vertical mounting seat; a lens is mounted inside the lens barrel, and the lens frame is an L-shaped structure, a mounting hole is provided on the transverse part of the lens frame, the holder is installed in the mounting hole, and the lens barrel is installed on the holder in the mounting hole, and the position of the lens barrel along the X-axis direction can be adjusted by rotating the lens barrel; one or more first waist-shaped adjustment grooves are provided along the length direction of the vertical mounting seat, and the vertical part of the lens frame is correspondingly mounted with the vertical mounting seat by means of a locking bolt and a nut; the transverse mounting seat is installed at one end of the vertical mounting seat, and the transverse mounting seat is provided with one or more second waist-shaped adjustment grooves along the X-axis direction, and the transverse mounting seat is mounted on the outer shell by means of a locking bolt and a nut.

3. The reverse-pumped high-power optical fiber amplifier according to claim 1 or 2, characterized in that: The clamping water cooling assembly includes a base, a clamping lower seat and a clamping upper seat; the base is installed inside the outer shell, the clamping lower seat can be detachably installed on the base, and the clamping upper seat can be detachably installed on the top of the clamping lower seat, the bottom of the clamping upper seat and the top of the clamping lower seat are both provided with V-shaped clamping grooves that cooperate with the outer side of the end cap for clamping and fixing, the clamping lower seat and the clamping upper seat are both made of copper, and cooling channels are provided inside the clamping lower seat and the clamping upper seat.

4. The reverse-pumped high-power optical fiber amplifier according to claim 3, characterized in that: The upper parts of the front and rear sides of the clamping lower seat are provided with U-shaped grooves, and the bottom of the U-shaped groove is installed with the base through fastening bolts. The front and rear sides of the bottom of the clamping upper seat are respectively provided with lateral extension ends, which respectively cooperate with the upper ends of the two side arms of the U-shaped groove and are fixedly installed by fastening bolts.

5. The reverse-pumped high-power optical fiber amplifier according to claim 4, characterized in that: A first cooling channel is formed inside the clamping lower seat, and a second cooling channel is formed inside the clamping upper seat. When the clamping lower seat and the clamping upper seat are installed correspondingly, the ports of the first cooling channel and the second cooling channel are connected to form a flow channel. Elastic sealing gaskets are provided at the ports of the first cooling channel and the second cooling channel, and one end of the elastic sealing gasket extends out of the corresponding docking surface of the clamping lower seat and the clamping upper seat.

6. The reverse-pumped high-power optical fiber amplifier according to any one of claims 3 to 5, characterized in that: A side water cooling pipe is arranged on the side of the outer shell.

7. The reverse-pumped high-power optical fiber amplifier according to claim 1, characterized in that: The outer shell is provided with two amplified light output ports, which respectively cooperate with the first dichroic mirror and the second dichroic mirror to reflect and output the amplified signal light. The amplified light output ports are installed with optical windows. The amplified light output ports that cooperate with the first dichroic mirror serve as detection ports, which are used to perform real-time power stability detection on the amplified signal light.

8. The reverse-pumped high-power optical fiber amplifier according to claim 3, characterized in that: The end cap includes a cylindrical end cap body, a guide rod is coaxially provided at one end of the end cap body, and a tapered connection portion is formed between the end cap body and the guide rod. The end of the amplification stage optical fiber is installed in the guide rod, and the V-shaped clamping groove contacts the outer side of the end cap body.

9. The reverse-pumped high-power optical fiber amplifier according to claim 1, characterized in that: The first dichroic mirror and the second dichroic mirror are both dichroic mirrors with coatings on both sides. The side of the dichroic mirror close to the first lens is provided with a high-transmittance film for transmitting the pump light collimated by the first lens, and the side of the dichroic mirror close to the second lens is provided with a high-reflection film for reflecting the signal light amplified by the amplifier-stage optical fiber coupling.

10. The reverse-pumped high-power optical fiber amplifier according to claim 1, characterized in that: The first lens and the second lens are plano-convex lenses, the opposite side of the first lens and the second lens is a focusing mirror surface, and the opposite side of the first lens and the second lens is a collimating mirror surface.

Images