Polarization-maintaining single-mode strongly tapered optical fiber combiner, preparation method and application thereof

Abstract

A polarization-maintaining single-mode strongly tapered fiber combiner, preparation method and application, including a polarization-maintaining single-mode fiber bundle, a common single-mode fiber bundle and a taper glass sleeve; the ends of each polarization-maintaining single-mode fiber in the polarization-maintaining single-mode fiber bundle are respectively fused with the thick end of a common single-mode fiber in the common single-mode fiber bundle to form N polarization-maintaining single-mode-common single-mode fibers of the combiner, and the taper glass sleeve is wrapped around the outside of the common single-mode fiber bundle; by strongly tapering the taper glass sleeve and the N common single-mode fibers that are closely arranged in a hexagonal close-packed array and penetrated into the taper glass sleeve, a taper zone is formed, and a fiber array end face is formed at the thin end of the common single-mode fiber bundle. The present invention is applied to a fiber laser coherent synthesis system, which can meet the requirements of a high duty cycle of the array beam, and can also realize a large number of beam synthesis and a larger angle of phased beam deflection under a small synthetic aperture.

Description

Technical Field

[0001] The invention relates to a polarization-maintaining single-mode strongly tapered optical fiber combiner and a coherent synthesis system, belonging to the technical field of optical fiber devices and optical fiber laser coherent synthesis. Background Art

[0002] Fiber laser coherent combining technology is considered to be one of the effective technical ways to obtain high-brightness lasers, and has broad application prospects in the fields of space optical communications, laser energy transmission, and laser radar. At present, the beam combining module in the coherent combining system is mainly implemented by spatial beam splicing technical solutions such as collimator arrays and microlens arrays, which have the following difficulties:

[0003] First, it is difficult to achieve large-angle deflection of the composite beam by phase control. The so-called phased beam deflection refers to the deflection of the beam by controlling the phase distribution of the unit beam in the coherent beam array. In this technology, the closer the size of the emitting unit is to the laser wavelength, the larger the phased deflection angle of the array beam will be. At present, the array element size in the microlens array synthesis scheme is the smallest, but it is still three orders of magnitude higher than the laser wavelength.

[0004] Secondly, in order to ensure a high array beam duty cycle and optical axis parallelism, the existing collimator array and microlens array solutions have complex systems, difficult installation and adjustment, large size and weight, and high cost. Summary of the invention

[0005] In view of the problems existing in the prior art, the purpose of the present invention is to provide a polarization-maintaining single-mode strongly tapered fiber combiner, a preparation method and an application, which can achieve a larger angle deflection of the array light beam and effectively reduce the complexity, installation difficulty, volume, weight and cost of the beam synthesis module in the fiber laser coherent synthesis system.

[0006] The technical solution of the present invention includes:

[0007] On the one hand, the present invention provides a polarization-maintaining single-mode strongly tapered optical fiber combiner, comprising a polarization-maintaining single-mode optical fiber bundle, a common single-mode optical fiber bundle and a tapered glass sleeve;

[0008] The polarization-maintaining single-mode optical fiber bundle is composed of N polarization-maintaining single-mode optical fibers;

[0009] The cone-area glass sleeve is wrapped around the outside of the common single-mode optical fiber bundle;

[0010] The common single-mode optical fiber bundle is composed of N common single-mode optical fibers, each of which has a thick end at one end and a thin end at the other end, and a cone section between the thick end and the thin end. The cone section includes a cone section and a cylindrical section. The cone section is close to the thick end of the common single-mode optical fiber, and the cylindrical section is close to the thin end of the common single-mode optical fiber.

[0011] The end of each polarization-maintaining single-mode optical fiber in the polarization-maintaining single-mode optical fiber bundle is fused with the thick end of an ordinary single-mode optical fiber in the ordinary single-mode optical fiber bundle to form N polarization-maintaining single-mode-ordinary single-mode optical fibers of the combiner. The optical axes of the N ordinary single-mode optical fibers in the cylindrical section are parallel to each other. The polarization directions of the light beams in the N polarization-maintaining single-mode-ordinary single-mode optical fibers are consistent. The ordinary single-mode optical fibers in the N polarization-maintaining single-mode-ordinary single-mode optical fibers are closely arranged in the form of a hexagonal close-packed array, and a fiber array end face is formed at the thin end of the ordinary single-mode optical fiber bundle.

[0012] Furthermore, the common single-mode optical fiber bundle and the tapered glass sleeve wrapped around the outside of the common single-mode optical fiber bundle are formed by strongly taper-ing the tapered glass sleeve and N common single-mode optical fibers that are closely arranged in a hexagonal close-packed array and penetrate into the tapered glass sleeve.

[0013] Furthermore, the diameter of the thin end of the common single-mode optical fiber after strong taper is smaller than the diameter of the common single-mode optical fiber before taper, so that the fiber cladding diameter of the thin end of the common single-mode optical fiber after strong taper can ensure that its output light beam is a single-mode laser.

[0014] Furthermore, the thick end diameter of the ordinary single-mode optical fiber after strong taper is equal to the diameter of the ordinary single-mode optical fiber before taper, the thin end diameter of the ordinary single-mode optical fiber after strong taper is the core diameter of the ordinary single-mode optical fiber before taper, and the cone section of the ordinary single-mode optical fiber after taper includes a cone section and a cylindrical section. The diameter of the cone section gradually changes from the thick end to the thin end, and the diameter of the cylindrical section keeps the diameter of the thin end unchanged to ensure that the optical axes of the output light beams of each single-mode optical fiber are parallel.

[0015] Furthermore, the fusion-splicing position of each polarization-maintaining single-mode optical fiber and the corresponding common single-mode optical fiber is at the same longitudinal position.

[0016] Furthermore, a fiber end cap or a rod lens collimator is fused to the thin end of the common single-mode optical fiber bundle.

[0017] On the other hand, the present invention provides a method for preparing the above-mentioned polarization-maintaining single-mode strongly tapered optical fiber combiner, comprising:

[0018] N polarization-maintaining single-mode optical fibers and N ordinary single-mode optical fibers are provided;

[0019] Each polarization-maintaining single-mode optical fiber is fused with a common single-mode optical fiber to obtain N fused polarization-maintaining single-mode-common single-mode optical fibers;

[0020] N polarization-maintaining single-mode-ordinary single-mode optical fibers that have been fused are closely arranged in a 60-degree V-groove in the form of a hexagonal close-packed array to form a polarization-maintaining single-mode-ordinary single-mode optical fiber bundle. The N polarization-maintaining single-mode-ordinary single-mode optical fibers in the polarization-maintaining single-mode-ordinary single-mode optical fiber bundle are parallel to each other, and the fusion position of each polarization-maintaining single-mode optical fiber in the N polarization-maintaining single-mode-ordinary single-mode optical fibers is kept consistent with the corresponding ordinary single-mode optical fiber as much as possible;

[0021] The polarization directions of the optical fibers in the polarization-maintaining single-mode-ordinary single-mode optical fiber bundle are adjusted in sequence to keep them consistent;

[0022] A cone-area glass sleeve is sleeved on one side of the ordinary single-mode optical fiber in the polarization-maintaining single-mode-ordinary single-mode optical fiber bundle to form a polarization-maintaining single-mode-ordinary single-mode optical fiber bundle with a cone-area glass sleeve, wherein the cone-area glass sleeve is located close to the optical fiber fusion point on the polarization-maintaining single-mode-ordinary single-mode optical fiber bundle, so that the length of the ordinary single-mode optical fiber after strong taper is as short as possible, the inner diameter size of the cone-area glass sleeve matches the size of the circumscribed circle of the polarization-maintaining single-mode-ordinary single-mode optical fiber bundle, and the length of the cone-area glass sleeve meets the taper requirement;

[0023] The polarization-maintaining single-mode-ordinary single-mode optical fiber bundle with the above-mentioned tapered glass sleeve is fixed to an optical fiber taper machine, and the tapered glass sleeve and N ordinary single-mode optical fibers that are closely arranged in a hexagonal close-packed array and penetrate into the tapered glass sleeve are strongly tapered together. When the diameter of the ordinary single-mode optical fiber after the strong taper reaches the preset size requirement, the strong taper is ended, and the center of the cylindrical section in the tapered section formed by the strong taper is cut to form the optical fiber array end face of the thin end of the ordinary single-mode optical fiber bundle, thereby obtaining the polarization-maintaining single-mode strongly tapered optical fiber combiner.

[0024] Furthermore, in the prepared polarization-maintaining single-mode strongly tapered fiber combiner: the thin end diameter of the ordinary single-mode optical fiber after strong taper is smaller than the diameter of the ordinary single-mode optical fiber before taper, so that the thin end diameter of the ordinary single-mode optical fiber after strong taper can ensure that its output light beam is a single-mode laser.

[0025] Furthermore, in the prepared polarization-maintaining single-mode strongly tapered optical fiber combiner: the thick end diameter of the ordinary single-mode optical fiber after strong tapering is equal to the diameter of the ordinary single-mode optical fiber before tapering, the thin end diameter of the ordinary single-mode optical fiber after strong tapering is the core diameter of the ordinary single-mode optical fiber before tapering, and the cone section diameter of the ordinary single-mode optical fiber after tapering gradually changes from the thick end to the thin end.

[0026] Furthermore, a fiber end cap or a rod lens collimator is fused at the thin end of the common single-mode fiber bundle to form a fiber combiner fused with a fiber end cap or a fiber combiner fused with a rod lens collimator.

[0027] On the other hand, the present invention applies the polarization-maintaining single-mode strongly tapered fiber combiner to a fiber laser coherent synthesis system. Since the diameter of the array light beam output by the polarization-maintaining single-mode strongly tapered fiber combiner is very small, a far field can be formed when the transmission distance is very short. Therefore, the spatial array light beam output by the polarization-maintaining single-mode strongly tapered fiber combiner can be directly detected by a photodetector after being transmitted through a spectroscope to obtain an evaluation function.

[0028] In the present invention, both common single-mode optical fiber and polarization-maintaining single-mode optical fiber are single-mode optical fibers. Single-mode optical fiber refers to an optical fiber that only allows the fundamental mode of the light beam to be transmitted, and the core diameter is usually small. Common single-mode optical fiber is relative to polarization-maintaining single-mode optical fiber. In order to achieve stronger birefringence, the internal structure of polarization-maintaining single-mode optical fiber has obvious stress areas, and it is not a circularly symmetrical structure. When the cone is strongly pulled, the insertion loss is too large. However, there is no stress area inside the common single-mode optical fiber, which is a circularly symmetrical structure. After the cone is strongly pulled, it is still a circularly symmetrical structure, and the insertion loss is very small. Typical models include SM980, HI1060, etc. There are different models for different bands.

[0029] Compared with the prior art, the technical effects that the present invention can produce are:

[0030] The diameter of the unit beam after combining is reduced to the order of 10 microns, which is about two orders of magnitude smaller than the minimum unit beam diameter (about 1 mm) of the current combining scheme while ensuring a high duty cycle. Therefore, the beam deflection angle achievable using the phased control method will increase by two orders of magnitude.

[0031] The angle of beam deflection achieved by phase control is given by OK. Among them, is the beam deflection angle, is the spacing between unit beams, is the phase difference between two adjacent light beams, is the laser wavelength. As can be seen from the above formula, when the duty cycle is kept high, the reduction of the unit beam diameter will make the spacing between the unit beams Reduces the beam deflection angle The present invention uses a strong taper method to make the diameter of the thin end of the common single-mode optical fiber after the strong taper much smaller than the diameter of the common single-mode optical fiber before the taper. Specifically, the diameter of the thin end of the common single-mode optical fiber after the strong taper is reduced to the order of 10 microns, which not only allows the array element beams to be closely arranged to achieve a high duty cycle, but also reduces the size of a single transmitting array element to only one order of magnitude higher than the laser wavelength, so that a larger angle of beam deflection can be achieved.

[0032] On the other hand, the polarization-maintaining single-mode strongly tapered fiber combiner proposed in the present invention ensures a high duty cycle, parallel optical axes and consistent polarization directions of the array light beams through a manufacturing process, and the device has a simple structure. Therefore, it has more advantages than existing technical solutions in terms of system complexity, installation complexity, volume and weight, and cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the specific implementation methods and technical solutions of the present invention, the drawings required for use in the specific implementation methods or prior art descriptions will be briefly introduced below. Obviously, the drawings in the following description are some implementation methods of the present invention. For ordinary technicians in this field, other example diagrams can be obtained based on these drawings without paying creative work.

[0034] Figure 1 It is a schematic diagram of the structure of a polarization-maintaining single-mode strongly tapered fiber combiner;

[0035] Figure 2 is a schematic diagram of a fiber combiner fused with fiber end caps;

[0036] Figure 3 is a schematic diagram of a fiber combiner fused with a rod lens collimator;

[0037] Figure 4 It is a schematic diagram of the structure of a coherent combining system based on a polarization-maintaining single-mode strongly tapered fiber combiner;

[0038] Numbers in the figure:

[0039] 1. Polarization-maintaining single-mode optical fiber; 2. Ordinary single-mode optical fiber; 3. Fusion point; 4. Fiber array end face; 5. Fiber end cap; 6. Rod lens collimator; 7. Cone glass sleeve;

[0040] 1-1, seed source laser; 1-2, fiber beam splitter; 1-3, phase modulator; 1-4, fiber amplifier; 1-5, polarization-maintaining single-mode strongly tapered fiber combiner; 1-6, beam splitter; 1-7, collimating lens; 1-8, photodetector; 1-9, controller. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings 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 making creative work are within the scope of protection of the present invention.

[0042] Reference Figure 1 , Figure 1 1 is a schematic structural diagram of a polarization-maintaining single-mode strongly tapered optical fiber combiner, wherein the polarization-maintaining single-mode strongly tapered optical fiber combiner provided by the present invention comprises a polarization-maintaining single-mode optical fiber bundle, a common single-mode optical fiber bundle and a tapered glass sleeve 7;

[0043] The polarization-maintaining single-mode optical fiber bundle is composed of N polarization-maintaining single-mode optical fibers 1;

[0044] The cone-area glass sleeve 7 is wrapped around the outside of the common single-mode optical fiber bundle;

[0045] The common single-mode optical fiber bundle is composed of N common single-mode optical fibers 2, each of which has a thick end at one end and a thin end at the other end, and a cone section is between the thick end and the thin end, and the cone section includes a cone section and a cylindrical section, the cone section is close to the thick end of the common single-mode optical fiber, and the cylindrical section is close to the thin end of the common single-mode optical fiber; the thick ends of the common single-mode optical fibers are closely arranged in the form of a hexagonal close-packed array to form the thick end of the common single-mode optical fiber bundle, and the thin ends of the common single-mode optical fibers 2 are closely arranged in the form of a hexagonal close-packed array to form the thin end of the common single-mode optical fiber bundle;

[0046] The end of each polarization-maintaining single-mode optical fiber 1 in the polarization-maintaining single-mode optical fiber bundle is fused with the thick end of a common single-mode optical fiber 2 in the common single-mode optical fiber bundle to form N polarization-maintaining single-mode-common single-mode optical fibers of the combiner. A fusion point 3 is formed at the fusion position of the polarization-maintaining single-mode optical fiber 1 and the common single-mode optical fiber 2. Preferably, the fusion position of each polarization-maintaining single-mode optical fiber 1 and the corresponding common single-mode optical fiber 2 is kept consistent as much as possible, that is, the positions of all fusion points 3 are kept consistent as much as possible.

[0047] The optical axes of the N ordinary single-mode optical fibers in the cylindrical section in the tapered section are parallel to each other, the polarization directions of the light beams in the N polarization-maintaining single-mode-ordinary single-mode optical fibers are consistent, the ordinary single-mode optical fibers in the N polarization-maintaining single-mode-ordinary single-mode optical fibers are closely arranged in the form of a hexagonal close-packed array, and a fiber array end face 4 is formed at the thin end of the ordinary single-mode optical fiber bundle.

[0048] The common single-mode optical fiber bundle and the tapered glass sleeve 7 wrapped around the outside of the common single-mode optical fiber bundle are formed by performing strong taper on the tapered glass sleeve and the N common single-mode optical fibers that are closely arranged in a hexagonal close-packed array and penetrate into the tapered glass sleeve. The tapered glass sleeve is strongly tapered together with the common single-mode optical fiber bundle to ensure that the relative positions of the optical fibers in the common single-mode optical fiber bundle remain unchanged during the strong taper process, and the common single-mode optical fiber bundle after the strong taper is protected.

[0049] The diameter of the thin end of the common single-mode optical fiber after the strong taper is smaller than the diameter of the common single-mode optical fiber before the taper, so that the fiber cladding diameter of the thin end of the common single-mode optical fiber after the strong taper can ensure that its output light beam is a single-mode laser. Specifically, the diameter of the thin end of the common single-mode optical fiber after the strong taper is reduced to the order of 10 microns, which not only allows the array element beams to be closely arranged to achieve a high duty cycle, but also reduces the size of the single-transmitting array element to only one order of magnitude higher than the laser wavelength, which can achieve a larger angle of beam deflection.

[0050] The thick end diameter of the common single-mode optical fiber after strong taper is equal to the diameter of the common single-mode optical fiber before taper, the thin end diameter of the common single-mode optical fiber after strong taper is equal to the core diameter of the common single-mode optical fiber before taper, the cone section of the common single-mode optical fiber after taper includes a cone section and a cylindrical section, the diameter of the cone section gradually changes from the thick end to the thin end, and the diameter of the cylindrical section keeps the diameter of the thin end unchanged to ensure that the optical axes of the output light beams of each single-mode optical fiber are parallel.

[0051] like Figure 1 As shown, taking a 7-way fiber combiner as an example, the polarization-maintaining single-mode fiber and the ordinary single-mode fiber after tapering are connected together by fusion splicing. The array light beams output from the thin end of the ordinary single-mode fiber bundle through the combiner are arranged together in a hexagonal close-packed form, and the fiber array end face 4 at the thin end of the ordinary single-mode fiber bundle is still in a hexagonal close-packed form. The polarization-maintaining single-mode strongly tapered fiber combiner is implemented by a strong taper method, that is, the thin end diameter of the ordinary single-mode fiber 2 after strong taper is smaller than the diameter of the ordinary single-mode fiber before tapering, so that the thin end diameter of the ordinary single-mode fiber after strong taper can ensure that its output light beam is a single-mode laser. Preferably, the thin end diameter of the ordinary single-mode fiber 2 after strong taper is the core diameter of the ordinary single-mode fiber before tapering, which is generally less than 10 microns. The advantage of doing this is that the diameter of the ordinary single-mode optical fiber bundle is drastically reduced after tapering, and the diameter of the thin end of a single-channel ordinary single-mode optical fiber is only equivalent to the size of a normal ordinary single-mode optical fiber core. At this time, the laser output by each ordinary single-mode optical fiber is still a single-mode laser, that is, the original optical fiber cladding is reduced to a new core, so the output light beams from the thin ends of each ordinary single-mode optical fiber can be closely arranged to meet the requirements of coherent synthesis for a high duty cycle of the array beam.

[0052] The polarization-maintaining single-mode optical fiber 1 can be a commercial polarization-maintaining single-mode optical fiber, and its specific model is selected by the user according to requirements such as output power and central wavelength.

[0053] The tapered ordinary single-mode optical fiber 2 can be a commercial single-mode optical fiber, which is fused with a polarization-maintaining single-mode optical fiber and then strongly tapered. Its model selection needs to match the mode field of the polarization-maintaining single-mode optical fiber to ensure that the insertion loss at the fusion point is as small as possible. The diameter of the ordinary single-mode optical fiber after tapering must be able to ensure that its output light beam is a single-mode laser.

[0054] The number of polarization-maintaining single-mode-ordinary single-mode optical fibers in the optical fiber combiner can be selected according to actual usage. Generally, the number of optical fibers corresponding to hexagonal close-packed arrays with different numbers of turns is selected, such as 7, 19, 37, etc.

[0055] The end face of the fiber combiner is made into an optical plane for fusion splicing by cutting or grinding. Further, a fiber end cap 5 or a rod lens collimator 6 is fused at the thin end of the common single-mode fiber bundle to form a fiber combiner fused with a fiber end cap or a fiber combiner fused with a rod lens collimator, such as Figure 2 and Figure 3 As shown, Figure 2 It is a schematic diagram of a fiber combiner with fiber end caps fused to it. Figure 3 This is a schematic diagram of a fiber combiner fused with a rod lens collimator. Since the divergence angle of the output beam of the fiber combiner is large, further collimation is required in long-distance applications. Therefore, in actual applications, a fiber combiner fused with a fiber end cap needs to add a collimator lens after the fiber end cap. The rod collimator lens in the fiber combiner fused with a rod lens collimator has a beam collimation function, and its output beam can be used directly.

[0056] On the other hand, the present invention provides a method for preparing the above-mentioned polarization-maintaining single-mode strongly tapered optical fiber combiner, comprising:

[0057] N polarization-maintaining single-mode optical fibers and N ordinary single-mode optical fibers are provided;

[0058] Each polarization-maintaining single-mode optical fiber is fused with a common single-mode optical fiber to obtain N fused polarization-maintaining single-mode-common single-mode optical fibers;

[0059] N polarization-maintaining single-mode-ordinary single-mode optical fibers that have been fused are closely arranged in a 60-degree V-groove in the form of a hexagonal close-packed array to form a polarization-maintaining single-mode-ordinary single-mode optical fiber bundle. The N polarization-maintaining single-mode-ordinary single-mode optical fibers in the polarization-maintaining single-mode-ordinary single-mode optical fiber bundle are parallel to each other, and the fusion position of each polarization-maintaining single-mode optical fiber in the N polarization-maintaining single-mode-ordinary single-mode optical fibers is kept consistent with the corresponding ordinary single-mode optical fiber as much as possible;

[0060] Adjust the polarization direction of each optical fiber in the polarization-maintaining single-mode-ordinary single-mode fiber bundle in turn to keep it consistent. The specific process is as follows: connect the output end of a polarization-maintaining single-mode fiber laser to the polarization-maintaining single-mode fiber of a certain optical fiber in the polarization-maintaining single-mode-ordinary single-mode fiber bundle, and ensure that the polarization direction of the laser output tail fiber is consistent with the polarization direction of the polarization-maintaining single-mode fiber in the polarization-maintaining single-mode-ordinary single-mode fiber bundle; place a polarizer and a power meter at the output end of the ordinary single-mode fiber, and rotate the position of the corresponding polarization-maintaining single-mode-ordinary single-mode fiber in the polarization-maintaining single-mode-ordinary single-mode fiber bundle to maximize the output value of the power meter. The optical fiber is adjusted and the position remains unchanged; disconnect the output end of the polarization-maintaining single-mode fiber laser and connect it to the next optical fiber to be adjusted. Adjust the polarization direction according to the above method until all optical fibers are adjusted. Then, the polarization directions of all optical fibers can be kept consistent. The consistency of polarization direction will affect the effect of coherent combining. The better the consistency, the better the coherent combining effect.

[0061] A cone-area glass sleeve is put on one side of the common single-mode optical fiber in the polarization-maintaining single-mode-common single-mode optical fiber bundle to form a polarization-maintaining single-mode-common single-mode optical fiber bundle with a cone-area glass sleeve, wherein the cone-area glass sleeve is located close to the optical fiber fusion point on the polarization-maintaining single-mode-common single-mode optical fiber bundle, so that the length of the common single-mode optical fiber after strong taper is as short as possible, and the inner diameter size of the cone-area glass sleeve matches the size of the circumscribed circle of the polarization-maintaining single-mode-common single-mode optical fiber bundle, and the length of the cone-area glass sleeve meets the taper demand. Due to the depolarization effect of the common single-mode optical fiber, the longer the length, the worse the polarization extinction ratio of the output beam. However, the polarization-maintaining single-mode optical fiber cannot be used to directly perform strong taper, because there is a stress rod in the polarization-maintaining single-mode optical fiber, and the laser transmittance will be seriously reduced after the strong taper. Therefore, the present invention adopts the method of fusing the polarization-maintaining single-mode optical fiber to the common single-mode optical fiber, and the method of strong taper of the common single-mode optical fiber can effectively avoid the above problems.

[0062] The polarization-maintaining single-mode-ordinary single-mode optical fiber bundle with the above-mentioned tapered glass sleeve is fixed to an optical fiber taper machine, and the tapered glass sleeve and N ordinary single-mode optical fibers that are closely arranged in a hexagonal close-packed array and penetrate into the tapered glass sleeve are strongly tapered together. When the diameter of the ordinary single-mode optical fiber after strong taper reaches the preset size requirement, the strong taper is ended, and the center of the cylindrical section in the tapered section formed by the strong taper is cut to form the optical fiber array end face of the thin end of the ordinary single-mode optical fiber bundle, thereby obtaining the polarization-maintaining single-mode strongly tapered optical fiber combiner.

[0063] In the prepared polarization-maintaining single-mode strongly tapered fiber combiner: the thin end diameter of the ordinary single-mode fiber after strong taper is smaller than the diameter of the ordinary single-mode fiber before taper, so that the thin end diameter of the ordinary single-mode fiber after strong taper can ensure that its output beam is a single-mode laser.

[0064] The present invention uses an optical fiber taper machine to strongly taper a single-mode optical fiber bundle in a polarization-maintaining single-mode-ordinary single-mode optical fiber bundle. When tapering, while ensuring the high transmission efficiency of a beam combiner, the length of the single-mode optical fiber is shortened as much as possible to weaken its influence on the polarization characteristics of the output optical beam.

[0065] The cone section of the beam combiner is a process of changing from thick to thin. The speed of change is determined by the length of the cone section. If the cone section is too short, the light beam will overflow from the cone section, and the transmission efficiency will be reduced. If the cone section is too long, the length of the ordinary single-mode optical fiber will be increased. Ordinary single-mode optical fiber has a depolarization effect, which will deteriorate the polarization characteristics of the linearly polarized light transmitted therein. The longer the depolarization effect, the more serious it is. Therefore, a compromise point needs to be taken. The length of the cone is determined according to the number of synthesized optical fibers and experience. Preferably, the length of the cone section is about 4 cm, of which the cone section is 3 cm long and the cylindrical section is 1 cm long.

[0066] In the prepared polarization-maintaining single-mode strongly tapered optical fiber combiner: the thick end diameter of the ordinary single-mode optical fiber after strong tapering is equal to the diameter of the ordinary single-mode optical fiber before tapering, the thin end diameter of the ordinary single-mode optical fiber after strong tapering is the core diameter of the ordinary single-mode optical fiber before tapering, and the cone section diameter of the ordinary single-mode optical fiber after tapering gradually changes from the thick end to the thin end.

[0067] The polarization-maintaining single-mode strongly tapered fiber combiner provided by the present invention is applied to a fiber laser coherent synthesis system. Since the diameter of the array light beam output by the polarization-maintaining single-mode strongly tapered fiber combiner is very small, a far field can be formed when the transmission distance is very short. Therefore, the spatial array light beam output by the polarization-maintaining single-mode strongly tapered fiber combiner can be directly detected by a photodetector after being transmitted through a spectroscope to obtain an evaluation function.

[0068] Reference Figure 4 , Figure 4 It is a structural schematic diagram of a coherent synthesis system constructed based on a polarization-maintaining single-mode strongly tapered fiber combiner. The fiber laser coherent synthesis system includes a seed source laser 1-1, a fiber beam splitter 1-2, a phase modulator 1-3, a fiber amplifier 1-4, a polarization-maintaining single-mode strongly tapered fiber combiner 1-5, a beam splitter 1-6, a collimating lens 1-7, a photodetector 1-8 and a controller 1-9; the polarization-maintaining single-mode strongly tapered fiber combiner 1-5 is a polarization-maintaining single-mode strongly tapered fiber combiner fused with a fiber end cap.

[0069] Applying the polarization-maintaining single-mode strongly tapered fiber combiner to the fiber laser coherent synthesis system can not only meet the requirements of high duty cycle of the array beam, but also realize large-number beam synthesis and larger-angle phased beam deflection under small synthetic aperture conditions, and effectively reduce the complexity, installation difficulty, and volume and weight of the beam synthesis module.

[0070] The output laser of the seed source laser 1-1 is divided into N sub-beams through the fiber beam splitter 1-2. The N sub-beams are phase modulated and power amplified by the corresponding phase modulator 1-3 and fiber amplifier 1-4, and then input into the polarization-maintaining single-mode strong tapered fiber combiner 1-5. The fiber end cap of the polarization-maintaining single-mode strong tapered fiber combiner 1-5 outputs it into space to form a spatial array beam. The spatial array beam is divided into two parts by the beam splitter 1-6. Most of the laser power is reflected by the beam splitter 1-6 and then output to the target through the collimating lens 1-7. A small part of the laser power is transmitted through the beam splitter 1-6 and output to the photodetector 1-8. Since the diameter of the array beam output by the fiber beam combiner is very small, a far field can be formed when the transmission distance is very short. Therefore, a photodetector can be used directly to detect after the beam splitter is transmitted to obtain an evaluation function. The photodetector 1-8 converts the detected far-field optical signal of the synthetic light beam into an electrical signal and transmits it to the controller 1-9. The controller 1-9 calculates the control signal based on the light intensity data and applies it to the corresponding phase modulator 1-3 to achieve phase locking of the array light beam.

[0071] The seed source laser 1-1 adopts a commercial single-frequency or narrow-linewidth polarization-maintaining single-mode fiber laser, and its output power and central wavelength are determined by the user according to system requirements.

[0072] The optical fiber beam splitter 1-2 adopts a commercial 1×N polarization-maintaining single-mode optical fiber beam splitter, whose input optical fiber model is the same as the output optical fiber model of the seed source laser, and can evenly divide the output laser power into N paths.

[0073] The phase modulator 1-3 can adopt a commercial fiber-coupled lithium niobate electro-optic phase modulator or a piezoelectric ceramic phase modulator, and the input fiber model is the same as the output fiber model of the fiber beam splitter.

[0074] The optical fiber amplifiers 1-4 can adopt commercial single-frequency or narrow-linewidth polarization-maintaining single-mode optical fiber laser amplifiers, the output power is determined by the user according to the needs, and the input power matches the output power of the phase modulator.

[0075] The polarization-maintaining single-mode strongly tapered fiber combiner 1-5 is prepared according to the preparation method provided in the aforementioned embodiment of the present invention.

[0076] The spectroscopes 1-6 can be commercial spectroscopes, whose aperture size meets the reflection requirements of the array beam and can withstand array beam laser irradiation. The splitting ratio increases the reflectivity as much as possible while ensuring that the transmitted laser power meets the detection requirements of subsequent photoelectric detectors, and the working wavelength is the output wavelength of the seed source laser.

[0077] The collimating lens 1-7 can be a commercial convex lens, and its aperture and focal length can be designed according to actual use requirements and can withstand the laser output power.

[0078] The photoelectric detectors 1-8 can be commercial photoelectric detectors, whose response band covers the wavelength of the seed source laser and whose detection sensitivity matches the received light intensity.

[0079] The controller 1-9 can be developed using a signal processor such as a single chip microcomputer, FPGA, DSP, etc., and can receive an electrical signal from a photodetector and generate a corresponding phase control signal to transmit to a phase modulator.

[0080] The polarization-maintaining single-mode strongly tapered fiber combiner provided by the present invention is mainly used in the aperture-divided fiber laser coherent synthesis system for array beam synthesis. In this application, it is required that the ordinary single-mode fiber bundle of the combiner has a high duty cycle after tapering, and a single-channel ordinary single-mode fiber can output a fundamental mode Gaussian beam. Therefore, a strong taper method is adopted to reduce the cladding size of each ordinary single-mode fiber after tapering to the size of the core, thereby meeting the requirements of high duty cycle and single-mode output at the same time. For example, if a 10 / 125 ordinary single-mode fiber (core diameter of 10 microns, cladding diameter of 125 microns) is selected for tapering, the cladding diameter of the ordinary single-mode fiber after tapering will change from 125 microns to 10 microns, which is equal to the core diameter of the ordinary single-mode fiber before tapering, and the ratio of the diameter of the ordinary single-mode fiber before and after tapering reaches 12.5. Usually, the fiber combiner is generally used for laser power synthesis or injecting pump light into the fiber laser, so the ratio of the fiber diameter before and after tapering is small, and it is not required that the cladding diameter of the fiber after tapering is strictly equal to the core diameter before tapering.

[0081] In the present invention, each polarization-maintaining single-mode-ordinary single-mode optical fiber in the polarization-maintaining single-mode strongly tapered optical fiber combiner comprises two parts, a polarization-maintaining single-mode optical fiber and an ordinary single-mode optical fiber, and it is required that the polarization direction of the output light beam after all polarization-maintaining single-mode-ordinary single-mode optical fibers are combined remains consistent. Polarization-maintaining single-mode optical fiber is used to make the laser output by each optical fiber in the combiner a good linear polarized light, meeting the requirements of coherent synthesis of array beams. However, the optical power loss of polarization-maintaining single-mode optical fiber is large after strong taper, so ordinary single-mode optical fiber is used in the cone area to reduce laser insertion loss. However, ordinary single-mode optical fiber has a depolarization effect, so the shorter the better, in order to minimize this effect. The solution of first fusing ordinary single-mode optical fiber and then tapering in the present invention is also to minimize the length of single-mode optical fiber as much as possible, ensuring that the output laser has good polarization-maintaining characteristics. Conventional optical fiber combiners generally use only one type of optical fiber on an input arm.

[0082] After the beam combiner in the present invention is tapered, the end cap or rod lens collimator is directly fused after the cone region is cut off, so that the input laser is directly output to space in the form of an array beam; and usually a fiber optic beam combiner will fuse a fiber after the cone region is cut off, so that multiple lasers are combined into one beam output in the fiber optic waveguide.

[0083] Matters not covered by the present invention are known technologies.

[0084] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0085] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

[0086] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. Polarization-maintaining single-mode strongly tapered fiber combiner, characterized in that: Including polarization-maintaining single-mode fiber bundle, common single-mode fiber bundle and tapered glass sleeve; The polarization-maintaining single-mode optical fiber bundle is composed of N polarization-maintaining single-mode optical fibers; The cone-area glass sleeve is wrapped around the outside of the common single-mode optical fiber bundle; The common single-mode optical fiber bundle is composed of N common single-mode optical fibers, each of which has a thick end at one end and a thin end at the other end, and a cone section between the thick end and the thin end. The cone section includes a cone section and a cylindrical section. The cone section is close to the thick end of the common single-mode optical fiber, and the cylindrical section is close to the thin end of the common single-mode optical fiber. The ends of each polarization-maintaining single-mode optical fiber in the polarization-maintaining single-mode optical fiber bundle are respectively fused with the thick end of an ordinary single-mode optical fiber in the ordinary single-mode optical fiber bundle to form N polarization-maintaining single-mode-ordinary single-mode optical fibers of the combiner, the optical axes of the N ordinary single-mode optical fibers in the cylindrical section are parallel to each other, the polarization directions of the light beams in the N polarization-maintaining single-mode-ordinary single-mode optical fibers are consistent, the ordinary single-mode optical fibers in the N polarization-maintaining single-mode-ordinary single-mode optical fibers are closely arranged in the form of a hexagonal close-packed array, and an optical fiber array end face is formed at the thin end of the ordinary single-mode optical fiber bundle, wherein the ordinary single-mode optical fiber bundle and the tapered glass sleeve wrapped around the outer side of the ordinary single-mode optical fiber bundle are formed by strongly tapering the tapered glass sleeve and the N ordinary single-mode optical fibers that are closely arranged in the form of a hexagonal close-packed array and penetrated into the tapered glass sleeve, and the thin end diameter of the ordinary single-mode optical fiber after the strong taper is smaller than the diameter of the ordinary single-mode optical fiber before the strong taper, so that The fiber cladding diameter of the thin end of the ordinary single-mode optical fiber after the taper can ensure that its output beam is a single-mode laser. The thick end diameter of the ordinary single-mode optical fiber after the strong taper is equal to the ordinary single-mode optical fiber diameter before the taper. The thin end diameter of the ordinary single-mode optical fiber after the strong taper is the core diameter of the ordinary single-mode optical fiber before the taper. The cone section of the ordinary single-mode optical fiber after the taper includes a cone section and a cylindrical section. The cone section diameter gradually changes from the thick end to the thin end, and the cylindrical section diameter keeps the thin end diameter unchanged to ensure that the optical axes of the output beams of each single-mode optical fiber are parallel. The diameter of the thin end of the ordinary single-mode optical fiber after the strong taper is reduced to the order of 10 microns, so that the array element beams are closely arranged to achieve a high duty cycle. The size of the single-emitting array element is also reduced to only one order of magnitude higher than the laser wavelength, which can achieve a larger angle of beam deflection. The beam deflection angle achievable by the phase-controlled method will increase by two orders of magnitude. The angle of beam deflection achieved by the phase-controlled method is given by the formula Sure, in, θ s is the beam deflection angle, d is the spacing between unit beams, Δ φ is the phase difference between two adjacent light beams, λ is the laser wavelength, 0≤Δ φ ≤2π, while maintaining a high duty cycle, the reduction in the unit beam diameter will make the spacing between unit beams d Reduces the beam deflection angle θ s Increase.

2. The polarization-maintaining single-mode strongly tapered optical fiber combiner according to claim 1, characterized in that: The thin end of the ordinary single-mode optical fiber bundle is fused with an optical fiber end cap or a rod lens collimator.

3. The method for preparing the polarization-maintaining single-mode strongly tapered optical fiber combiner according to claim 1, characterized in that: include: N polarization-maintaining single-mode optical fibers and N ordinary single-mode optical fibers are provided; Each polarization-maintaining single-mode optical fiber is fused with a common single-mode optical fiber to obtain N fused polarization-maintaining single-mode-common single-mode optical fibers; N polarization-maintaining single-mode-ordinary single-mode optical fibers that have been fused are closely arranged in a 60-degree V-groove in the form of a hexagonal close-packed array to form a polarization-maintaining single-mode-ordinary single-mode optical fiber bundle, wherein the N polarization-maintaining single-mode-ordinary single-mode optical fibers in the polarization-maintaining single-mode-ordinary single-mode optical fiber bundle are parallel to each other, and the fusion position of each polarization-maintaining single-mode optical fiber in the N polarization-maintaining single-mode-ordinary single-mode optical fibers is consistent with that of the corresponding ordinary single-mode optical fiber; The polarization directions of the optical fibers in the polarization-maintaining single-mode-ordinary single-mode optical fiber bundle are adjusted in sequence to keep them consistent; A cone-area glass sleeve is sleeved on one side of the common single-mode optical fiber in the polarization-maintaining single-mode-common single-mode optical fiber bundle to form a polarization-maintaining single-mode-common single-mode optical fiber bundle with a cone-area glass sleeve, wherein the cone-area glass sleeve is located close to the optical fiber fusion point on the polarization-maintaining single-mode-common single-mode optical fiber bundle, the inner diameter of the cone-area glass sleeve matches the circumscribed circle size of the polarization-maintaining single-mode-common single-mode optical fiber bundle, and the length of the cone-area glass sleeve meets the taper drawing requirement; The polarization-maintaining single-mode-ordinary single-mode optical fiber bundle with the tapered glass sleeve is fixed to an optical fiber taper machine, and the tapered glass sleeve and N ordinary single-mode optical fibers that are closely arranged in a hexagonal close-packed array and inserted into the tapered glass sleeve are strongly tapered together. When the diameter of the ordinary single-mode optical fiber after the strong taper reaches the preset size requirement, the strong taper is ended, and the cylindrical section in the tapered section formed by the strong taper is cut in the center to form the optical fiber array end face of the thin end of the ordinary single-mode optical fiber bundle, and the polarization-maintaining single-mode strongly tapered optical fiber combiner is obtained. In the prepared polarization-maintaining single-mode strongly tapered optical fiber combiner: the ordinary single-mode optical fiber after the strong taper The diameter of the thick end of the single-mode fiber is equal to the diameter of the ordinary single-mode fiber before the taper, the diameter of the thin end of the ordinary single-mode fiber after the strong taper is the core diameter of the ordinary single-mode fiber before the taper, and the cone section diameter of the ordinary single-mode fiber after the taper gradually changes from the thick end to the thin end. The diameter of the thin end of the ordinary single-mode fiber after the strong taper is reduced to the order of 10 microns, so that the array element beams are closely arranged to achieve a high duty cycle, and the size of the single-emitting array element is reduced to only one order of magnitude higher than the laser wavelength, which can achieve a larger angle of beam deflection. The beam deflection angle that can be achieved by the phase-controlled method will increase by two orders of magnitude. The angle of beam deflection achieved by the phase-controlled method is given by the formula Sure, in, θ s is the beam deflection angle, d is the spacing between unit beams, Δ φ is the phase difference between two adjacent light beams, λ is the laser wavelength, 0≤Δ φ ≤2π, while maintaining a high duty cycle, the reduction in the unit beam diameter will make the spacing between unit beams d Reduces the beam deflection angle θ s Increase.

4. The method for preparing a polarization-maintaining single-mode strongly tapered optical fiber combiner according to claim 3, characterized in that: A fiber end cap or a rod lens collimator is fused at the thin end of a common single-mode fiber bundle to form a fiber combiner fused with a fiber end cap or a fiber combiner fused with a rod lens collimator.

5. The application of the polarization-maintaining single-mode strongly tapered fiber combiner in a fiber laser coherent combining system as claimed in claim 1, characterized in that: The fiber laser coherent synthesis system comprises a seed source laser, a fiber beam splitter, a phase modulator, a fiber amplifier, a polarization-maintaining single-mode strongly tapered fiber combiner, a beam splitter, a collimating lens, a photodetector and a controller; the polarization-maintaining single-mode strongly tapered fiber combiner is a polarization-maintaining single-mode strongly tapered fiber combiner fused with a fiber end cap; The output laser of the seed source laser is divided into N sub-beams by a fiber beam splitter. The N sub-beams are respectively phase-modulated and power-amplified by the corresponding phase modulator and fiber amplifier and then input into a polarization-maintaining single-mode strongly tapered fiber combiner. The sub-beams are output into space through the fiber end cap of the polarization-maintaining single-mode strongly tapered fiber combiner to form a spatial array beam. The spatial array beam is divided into two parts by a beam splitter. Most of the laser power is reflected by the beam splitter and output to the target, and a small part of the laser power is transmitted by the beam splitter and output to the photodetector. The photodetector converts the detected far-field optical signal of the synthetic beam into an electrical signal and transmits it to the controller. The controller calculates the control signal based on the light intensity data and applies it to the phase modulator to achieve phase locking of the array beam.

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