Optical fiber end face pump-signal coupler, method of manufacture and use

Abstract

The application discloses an optical fiber end face pump-signal coupler, a preparation method and application, and relates to the technical field of optical fiber end face pump-signal couplers.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fiber laser, in particular to a fiber end-face pump-signal coupler, a preparation method and application thereof. BACKGROUND

[0002] At present, fiber lasers have been widely used in many fields including industrial processing, medical surgery and national defense technology due to high conversion efficiency, good beam quality and convenient heat management. As one of the core devices of fiber lasers, pump-signal coupler determines the pumping capacity of the system, and its performance directly affects the output power level of the laser. With the continuous expansion of the application demand of lasers, the requirements for passive devices are also increasing. For example, lasers used in some extreme environments require their components to work stably in vacuum, strong vibration and high irradiation. As a core passive device of fiber lasers, the performance improvement of fiber end-face pump-signal coupler, especially the stability improvement under extreme environment, is crucial.

[0003] From the coupling mechanism of the device, fiber pump-signal coupler can be divided into end-face pump coupler and side-face pump coupler. The end-face pump coupler refers to coupling pump light into the inner cladding from the end face of the signal fiber, while the side-face pump coupler refers to coupling pump light into the inner cladding from the side face of the signal fiber.

[0004] At present, end-face pump coupler can be generally divided into N×1 type fiber end-face pump coupler (without signal fiber) and (N+1)×1 type fiber end-face pump-signal coupler (centered on signal fiber). Compared with N×1 type fiber end-face pump coupler (without signal fiber), the advantage of (N+1)×1 type fiber end-face pump-signal coupler (centered on signal fiber) is that it can be used in laser amplifiers or backward-pumped structure lasers.

[0005] The preparation method of the fiber end face pump-signal coupler of the (N+1) * 1 type comprises the following steps: firstly, N multimode pump fibers are tightly surrounded around a signal fiber to form a bundle; the bundle is cut from the middle of the waist region; and finally, the cut taper is fused with a double-clad output signal fiber. However, in general, the bundle is directly tapered to the size of the inner cladding of the output signal fiber, and the bundle is cut and fused to complete the preparation of the coupler. The disadvantage of this scheme is that the signal fiber will also be reduced in proportion during the tapering process, which may cause the core mode field of the input and output signal fibers to be mismatched, thereby affecting the signal transmission quality. In this method, for a given output signal fiber, the specific core and cladding sizes of the input signal / pump fiber need to be considered and selected to ensure the transmission efficiency of the signal light and the tightness of the bundle, which greatly reduces the practicability of the coupler. In addition, when the tapering ratio of the pump fiber in the bundle is too large, the brightness of the pump light transmitted in the pump fiber will be significantly degraded, which may cause a sharp temperature rise at the stripping opening of the coating layer of the output signal fiber, thereby affecting the use of the device at high power. SUMMARY

[0006] In view of the technical problems existing in the prior art, the present application provides a fiber end face pump-signal coupler, a preparation method and an application.

[0007] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0008] On the one hand, the present application provides a preparation method of a fiber end face pump-signal coupler, comprising the following steps:

[0009] The pump fibers are pretreated, the pretreated pump fibers and a hollow glass tube are twisted and knotted, and the pump fibers are heated and tapered to form a primary bundle, wherein the hollow glass tube is located at the center position, and the pump fibers are tightly combined around the hollow glass tube;

[0010] The signal fiber is pretreated, the pretreated signal fiber is inserted into the hollow glass tube of the primary bundle to form a secondary bundle;

[0011] The secondary bundle is re-bundled to form a tertiary bundle;

[0012] The tertiary bundle is cut and fused with an output signal fiber to complete the preparation of the fiber end face pump-signal coupler.

[0013] Further, the application pre-processes the pump optical fiber, including: stripping a certain length of coating layer of a middle section of each pump optical fiber to form a bare fiber section, the bare fiber section of the pump optical fiber comprising a cladding and a core, the cladding wrapping the core, and etching the bare fiber section of the pump optical fiber using a hydrofluoric acid solution to form an etching taper region, an etching waist region, and an etching roughened portion.

[0014] Further, the application provides a method for primary bundling, including:

[0015] Two porous twist clamps are provided, and the two porous twist clamps are oppositely arranged, wherein the porous twist clamp comprises a clamp body, and a plurality of through holes are arranged on the clamp body, wherein one through hole is a center hole, and the remaining plurality of through holes are uniformly distributed in a ring shape around the center hole with the center hole as the center.

[0016] A hollow glass tube is provided, the hollow glass tube is inserted into the center hole of the two porous twist clamps, and the pre-processed pump optical fibers are inserted into the through holes around the center hole of the two porous twist clamps one by one.

[0017] The pump optical fibers and the hollow glass tube are tightly combined together by twisting the porous twist clamps.

[0018] The twisted fiber bundle is heated and tapered to form a taper region, the primary bundling is completed, and a primary bundled fiber bundle is obtained.

[0019] Further, the outer diameter of the taper region of the primary bundled fiber bundle is consistent with the outer diameter of the inner cladding of the output signal optical fiber.

[0020] Further, the application pre-processes the signal optical fiber, including: stripping a certain length of coating layer of a first end of the signal optical fiber to form a bare fiber section, and etching a free end of the bare fiber section of the signal optical fiber to form a taper-waist end, the taper-waist end comprising a taper region with a certain length and a waist region with a certain length, and the waist region being located at the outermost end.

[0021] Further, the taper-waist end of the pre-processed signal optical fiber is inserted into the hollow glass tube in the primary bundled fiber bundle to complete a secondary bundled fiber bundle.

[0022] Further, the application provides a re-bundling process for the secondary bundled fiber bundle, including: heating and weakly tapering the secondary bundled fiber bundle using a heat source, and the entire weak tapering process does not change the core size of the input signal optical fiber, so that the signal optical fiber is fused together with the hollow glass tube and the pump optical fiber, and a tertiary bundled fiber bundle is obtained.

[0023] Further, the application provides a process for fusion splicing the tertiary bundled fiber bundle after flat cutting and an output signal optical fiber, including:

[0024] The three-bundle fiber bundle is flatly cut, and the end of the three-bundle fiber bundle after cutting is flatly cut and a waist region of a certain length of signal fiber is reserved;

[0025] The output signal fiber is pretreated, a certain length of coating layer of one end of the output signal fiber is stripped to form a bare fiber segment, the bare fiber segment of the output signal fiber is wiped clean with an acetone or alcohol solution, and finally the end of the bare fiber segment of the output signal fiber is flatly cut;

[0026] The three-bundle fiber bundle after flat cutting is fused with the output signal fiber by using a fusion machine to complete preparation of the fiber end face pump-signal coupler.

[0027] Further, the prepared fiber end face pump-signal coupler is packaged in a glass clamp.

[0028] On the other hand, the application provides a fiber end face pump-signal coupler prepared according to the preparation method of the fiber end face pump-signal coupler.

[0029] On the other hand, the application provides a fiber laser, comprising a seed laser and a plurality of pump lasers, which are coupled and connected through the fiber end face pump-signal coupler prepared according to the preparation method of the fiber end face pump-signal coupler.

[0030] Compared with the prior art, the application can produce the following technical effects:

[0031] In the primary bundling process of the application, the pre-processed multiple pump fibers and the hollow glass tube are twisted and knotted, heated and tapered to complete the primary bundling. On the one hand, the primary bundling is performed by using the twisting method, and the tapering ratio of the pump fiber is much smaller than that of the general sleeve method. Therefore, the fiber end face pump-signal coupler produced in this way can effectively alleviate the temperature rise caused by the degradation of the pump light brightness when applied to the fiber laser. On the other hand, the signal fiber does not participate in the primary bundling, i.e. does not participate in the twisting and knotting and heating and tapering of the primary bundling. The stress introduced by the simultaneous twisting of the signal fiber and the pump fiber can be avoided. The process of twisting and knotting and heating and tapering is participated in, and the stress of the central signal fiber can be effectively eliminated. Therefore, the fiber end face pump-signal coupler produced in this way can maintain the transmission quality of the signal light in the signal fiber when applied to the fiber laser.

[0032] In the secondary beam bundle, the signal fiber and the pump fiber are bundled by means of the hollow glass tube, the input signal fiber is not tapered, the insertion loss caused by the mismatch of the core mode field of the input and output signal fibers in the fiber end face pump-signal coupler is improved. In addition, no torsional stress is applied to the signal fiber during the entire preparation process, effectively ensuring the beam quality characteristics of the device.

[0033] The secondary beam bundle is re-bundled, including: the secondary beam bundle is heated and weakly tapered by a heat source, the core size of the input signal fiber is not changed during the entire weak tapering process, the signal fiber is bonded with the hollow glass tube and the pump fiber, and a tertiary beam bundle is obtained. In this way, the fiber end face pump-signal coupler is finally prepared through primary beam bundling, secondary beam bundling and re-bundling. The signal fiber does not participate in torsion during the entire preparation process, and only the secondary beam bundle is heated and weakly tapered by a heat source during the re-bundling process, the core size of the input signal fiber is not changed during the entire weak tapering process, thereby avoiding the insertion loss caused by the mismatch of the core mode field of the input and output signal fibers in the fiber end face pump-signal coupler. In addition, no torsional stress is applied to the signal fiber during the entire preparation process, effectively ensuring the beam quality characteristics of the device. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative labor based on the drawings shown.

[0035] Figure 1 The flow chart of the preparation method of the fiber end face pump-signal coupler provided for an embodiment;

[0036] Figure 2 The structure diagram of the roughened and etched pump fiber in an embodiment;

[0037] Figure 3 The structure diagram of the seven-hole torsion clamp used in an embodiment;

[0038] Figure 4 The primary beam bundling diagram in an embodiment;

[0039] Figure 5 The diagram of completing the primary beam bundling by torsion knotting and heating tapering in an embodiment;

[0040] Figure 6 The structure diagram of the pretreated signal fiber in an embodiment;

[0041] Figure 7 FIG. 1 is a structural schematic diagram of a fiber end-pumped signal coupler prepared in an embodiment;

[0042] Figure 8 FIG. 2 is a structural schematic diagram of a glass clamp for packaging the fiber end-pumped signal coupler provided in an embodiment. DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0044] Reference Figure 1 In an embodiment, a preparation method of a fiber end-pumped signal coupler is provided, comprising:

[0045] The pump fibers are pretreated, and the pretreated pump fibers and the hollow glass tube are twisted and knotted, heated and tapered to complete primary bundling, to obtain a primary bundled fiber bundle;

[0046] The hollow glass tube is located at a central position in the primary bundled fiber bundle, and the pump fibers are tightly combined around the hollow glass tube at the periphery of the hollow glass tube;

[0047] The signal fibers are pretreated, and the pretreated signal fibers are inserted into the hollow glass tube in the primary bundled fiber bundle to complete secondary bundling, to obtain a secondary bundled fiber bundle;

[0048] The secondary bundled fiber bundle is subjected to re-bundling treatment to obtain a tertiary bundled fiber bundle;

[0049] After the tertiary bundled fiber bundle is cut flat, the tertiary bundled fiber bundle is fused with the output signal fibers to complete preparation of the fiber end-pumped signal coupler.

[0050] Compared with the general twisting method in the above embodiments, the above embodiments can avoid the signal fibers from participating in the twisting and tapering process of the pump fibers by introducing the hollow glass tube to assist in bundling the signal fibers and the pump fibers, thereby effectively eliminating the stress of the central signal fibers. The fiber end-pumped signal coupler prepared in this way can effectively maintain the transmission quality of the signal light when applied to a fiber laser system.

[0051] In addition, in the above embodiment, the signal fiber and the pump fiber are bundled by means of the hollow glass tube, the signal fiber is inserted into the hollow glass tube of the primary bundled fiber bundle, the stress introduced by twisting the signal fiber and the pump fiber at the same time is eliminated, and the long-term stability of the output spot of the combiner is improved. On the other hand, the signal fiber is not tapered at all in the present application, and the insertion loss introduced by the mismatch of the core mode field of the input and output signal fibers in the pump coupler is improved. In addition, no torsional stress is applied to the signal fiber during the entire preparation process, and the beam quality characteristics of the device are effectively ensured.

[0052] Further, in an embodiment, a method for pre-processing the pump fiber is provided, comprising: stripping a certain length of coating layer from the middle section of each pump fiber to form a bare fiber section 1, the bare fiber section 1 of the pump fiber comprising a cladding and a core, the cladding wrapping the core, and etching and roughening the bare fiber section of the pump fiber by using a hydrofluoric acid solution to form an etching taper region 12, an etching waist region 13, and an etching roughening part 11, as shown in Figure 2 The structure of the pump fiber after etching and roughening in an embodiment is shown in the figure, wherein 14 represents the diameter of the etching waist region of the pump fiber after etching. By etching and roughening the bare fiber section of the pump fiber by using a hydrofluoric acid solution, on the one hand, the tapering proportion of the core of the pump fiber can be further reduced, and on the other hand, when the finally obtained fiber end face pump-signal coupler is applied to a fiber laser system, due to the existence of the etching roughening part of the pump fiber in the fiber end face pump-signal coupler, the severe temperature rise caused by back light at the etching roughening part can be prevented, the problem of heating of the coating layer of the output signal fiber caused by degradation of the pump light brightness can be effectively alleviated, and the stability of the device under high-power operation is improved. Further, by etching and roughening the bare fiber section of the pump fiber by using a hydrofluoric acid solution, when the finally prepared fiber end face pump-signal coupler is applied to a fiber laser system with a backward pumping structure, the damage of the pump source caused by the incompletely absorbed pump light and the partially leaked signal light in the backward application can be effectively prevented, and the safety of the pump source is protected.

[0053] In an embodiment, a primary bundling method is provided, comprising:

[0054] Referring to Figure 4 Two multi-hole twist clamps 2 are provided, and the two multi-hole twist clamps 2 are oppositely arranged, wherein the multi-hole twist clamp 2 comprises a clamp body, and a plurality of through holes 21 are arranged on the clamp body, one of which is a center hole, and the remaining plurality of through holes are uniformly distributed in a ring shape around the center hole with the center hole as the center;

[0055] The hollow glass tube 32 is inserted into the center hole of the two porous twist clamps 2, and the pre-processed pump optical fibers 31 are inserted into the through holes around the center hole of the two porous twist clamps.

[0056] Referring to Figure 3 Fig. 2 is a structural schematic diagram of a seven-hole twist clamp used in an embodiment, the porous twist clamp 2 includes a clamp body, and the clamp body is provided with seven through holes 21, one of which is a center hole, and the remaining through holes are uniformly distributed in a ring around the center hole.

[0057] Referring to Figure 5 The pump optical fibers 31 and the hollow glass tube 32 are tightly combined together by twisting the porous twist clamp 2, the twisted fiber bundle is heated and tapered to form a taper zone, the primary assembly is completed, and a primary assembly fiber bundle is obtained. In the present application, the outer diameter of the taper zone of the primary assembly fiber bundle is consistent with the outer diameter of the inner cladding of the output signal optical fiber. In this way, the fabrication of the fiber end face pump-signal coupler based on any size signal optical fiber and any size pump optical fiber can be realized, and the input and output signal optical fiber modes can be completely matched. The fiber end face pump-signal coupler prepared finally does not introduce beam quality degradation and signal efficiency when used in reverse, and has extremely high practical value.

[0058] In this way, the present application corrodes and roughens the bare fiber section of the pump optical fiber by using a hydrofluoric acid solution, completes the assembly of the signal optical fiber and the pump optical fiber by means of the hollow glass tube, does not twist and taper the signal optical fiber at all, realizes a back light prevention function, effectively ensures the beam quality characteristics of the device, can prepare a (N+1)×1 type fiber end face pump-signal coupler based on any optical fiber size, considers and optimizes the preparation scheme from multiple aspects, effectively improves the performance of the prepared fiber end face pump-signal coupler in all aspects, ensures the stability of the prepared fiber end face pump-signal coupler working in extreme environments, and further lays a foundation for realizing higher power, higher beam quality, and more stable fiber lasers.

[0059] In an embodiment, a method for pre-processing an input signal optical fiber is provided, which includes: stripping a certain length of signal optical fiber coating 51 from the first end of the signal optical fiber 5 to form a bare fiber section 52, and corroding the free end of the bare fiber section 52 of the signal optical fiber 5 to form a taper-waist end, the taper-waist end includes a taper zone 53 with a certain length and a waist zone 54 with a certain length, and the waist zone 54 is located at the outermost end. Figure 6 , Figure 6Figure 1 is a schematic diagram of a signal fiber structure after pretreatment in an embodiment. The diameter of the taper region of the taper-waist end is determined by the inner diameter of the hollow glass tube after drawing, and the length is about 5 cm. The taper-waist end of the signal fiber after pretreatment is inserted into the hollow glass tube after drawing, and the taper-waist end of the signal fiber is located in the taper-waist section of the hollow glass tube after drawing, thereby completing the secondary bundled fiber bundle.

[0060] Next, the secondary bundled fiber bundle is subjected to re-bundling treatment, which includes heating and weakly drawing the secondary bundled fiber bundle by using a heat source, and the whole weak drawing process does not change the core size of the input signal fiber, so that the signal fiber, the hollow glass tube and the pump fiber are fused together at high temperature, thereby obtaining a tertiary bundled fiber.

[0061] The tertiary bundled fiber bundle is subjected to flat cutting, and the end of the tertiary bundled fiber bundle after cutting is required to be flat and to retain a certain length of the waist region of the signal fiber; that is, the tertiary bundled fiber bundle is subjected to flat cutting from the waist region of the tertiary bundled fiber.

[0062] The output signal fiber is subjected to pretreatment, and the output signal fiber 6 includes an output signal fiber coating layer 61 and an output signal fiber cladding layer 62. One end of the output signal fiber is stripped of a certain length of the coating layer to form a bare fiber section, and the bare fiber section of the output signal fiber is wiped clean with an acetone or alcohol solution, and finally the end of the bare fiber section of the output signal fiber is cut flat.

[0063] The tertiary bundled fiber bundle after flat cutting is fused with the pretreated output signal fiber by using a fusion machine, thereby completing the preparation of the fiber end face pump-signal coupler. Figure 7 Figure 2 is a schematic diagram of the fiber end face pump-signal coupler after fusion in an embodiment.

[0064] Further, after flat cutting of the tertiary bundled fiber bundle, the end of the tertiary bundled fiber bundle after cutting is feedback aligned and fused with the output signal fiber, and the beam quality M 2 factor or power is used as the feedback reference quantity to reduce the off-axis loss during fusion, and the feedback reference quantity can also be used to evaluate the good or bad of the fusion parameters, so that the fusion parameters can be improved in time.

[0065] The present application is based on the etching method of the input signal fiber and the drawing method of the pump fiber, and can realize the manufacture of the pump / signal coupler based on the sizes of any signal fiber and pump fiber, the input and output signal fiber modes can be completely matched, and the reverse use will not introduce beam quality degradation and signal efficiency. It has very high practical value.

[0066] The preparation method of the fiber end face pump-signal coupler provided by the embodiment further requires that the etching degree of the pump fiber and the tapering degree of the pump fiber after etching meet the following requirements: the etching of the pump fiber cladding cannot be too large, and a cladding diameter greater than 5 μm is required to be left after etching to prevent the pump light from leaking. The signal fiber is etched according to the size of the inner diameter of the hollow glass tube, and the etched signal fiber is inserted into the taper formed by the tapering of the hollow glass tube to complete the bundling. The waist taper end of the signal fiber has a waist end face diameter substantially the same as the inner diameter of the hollow glass tube after tapering, to meet the requirement of close bundling. The fiber bundle end face after bundling has a diameter the same as the inner cladding diameter of the input signal fiber after stripping and coating. The fiber bundle end face after bundling and meeting the above requirements is cut and flattened, and then low-loss feedback fusion is performed with the output signal fiber, to reduce the signal insertion loss caused by off-axis. The fiber end face pump-signal coupler after fusion is packaged in a nested glass tube using ultraviolet curing glue, and the two ends of the nested glass tube are sealed with sealing glue, so that the fiber end face pump-signal coupler packaged in the nested glass tube can be isolated from the external environment, and the stability of the coupler in extreme environments is enhanced.

[0067] To ensure the mode field matching of the input and output signal fiber cores of the combiner, the input signal fiber and the output signal fiber of the present application have the same fiber type, and then the etching ratio of the input signal fiber and the tapering ratio of the pump fiber are determined according to the inner cladding size of the output signal fiber.

[0068] Further, the prepared fiber end face pump-signal coupler is packaged in a glass clamp. The fiber end face pump-signal coupler after fusion is sealed in a specially designed nested glass tube by ultraviolet curing glue, completely isolated from the external environment, and the stability of the device is improved.

[0069] Figure 8The structural diagram of the glass fixture for packaging the fiber end-pumped signal coupler provided in an embodiment includes a semi-cylindrical glass tank 71 and a cylindrical glass tube 72. The fiber end-pumped signal coupler after fusion is fixed in the semi-cylindrical glass tank 71 by ultraviolet curing glue, and the coating layer of the output fiber is coated with low refractive index ultraviolet glue at the stripping position to reduce the temperature rise at the position. Then the semi-cylindrical glass tank 71 is inserted into the cylindrical glass tube 72 together with the fiber end-pumped signal coupler, and the two ends of the cylindrical glass tube 72 are sealed with high refractive index ultraviolet glue. The packaging purpose of the fiber end-pumped signal coupler is mainly as follows: firstly, it plays a heat dissipation function. When the fiber end-pumped signal coupler is applied to the fiber laser, the semi-cylindrical glass tank 71 and the cylindrical glass tube 72 can effectively conduct the leaked laser and the generated waste heat in the fiber end-pumped signal coupler out, thereby improving the power bearing capacity of the fiber end-pumped signal coupler; secondly, it isolates the interference of the external environment, increases the stability of the long-time operation of the fiber end-pumped signal coupler, and prolongs the service life of the fiber end-pumped signal coupler. Compared with the traditional packaging fixture, the glass fixture has only two ends directly in contact with the air, and the sealing performance is more favorable to ensure that the glass tube is sealed by the sealing glue, so that the fiber end-pumped signal coupler can be effectively isolated from the external environment. In the embodiment, the fiber end-pumped signal coupler is placed in the semi-cylindrical glass tank 71, and the cylindrical glass tube 72 is sealed. As long as the two ends of the cylindrical glass tube 72 are tightly sealed, the tightness of the fiber end-pumped signal coupler can be ensured. When the fiber end-pumped signal coupler is applied to the fiber laser, the scattered light of the fiber end-pumped signal coupler can be transmitted to the air, and no additional heat is absorbed by the fiber end-pumped signal coupler, which is conducive to the long-term stable operation of the fiber end-pumped signal coupler.

[0070] In an embodiment of the present application, an (N+1)×1 fiber end-pumped signal coupler is prepared based on the preparation method of the fiber end-pumped signal coupler provided in the present application. In the embodiment, the input signal fiber and the output signal fiber both adopt double-cladding signal cladding fibers with a core / cladding size of 25 / 400 μm (NA=0.06 / 0.46), and the embodiment has six double-cladding pump fibers with a structure parameter of 220 / 242 μm (NA=0.22).

[0071] 1) Preprocessing of the pump fiber:

[0072] Figure 2Fig. 1 is a schematic diagram of the structure of the pump fiber after the hair-like corrosion in an embodiment, mainly comprising a pump fiber 1, the pump fiber 1 adopts a 220 / 242 μm (NA=0.22) double-clad fiber, wherein 11 is a hair-like region of the fiber, the length is about 1.5 cm, 12 is a corrosion taper region, 13 is a corrosion waist region, the diameter of the corrosion waist region is about 230 μm, and 14 represents the diameter of the corrosion waist region of the pump fiber after the corrosion.

[0073] The specific processing method is as follows: six 220 / 242 μm (NA=0.22) double-clad pump fibers are prepared, the coating layer of each 220 / 242 μm (NA=0.22) double-clad pump fiber is stripped off to a length of about 8 cm, and the fiber cladding surface is cleaned with anhydrous ethanol. Then, a corrosion agent prepared by mixing 55% concentrated hydrofluoric acid and glass frosting paste is used to hair-like the cladding at a distance of 4 cm from the stripped end of the pump fiber coating layer, and the length is 1.5 cm. Then, high-purity hydrofluoric acid is used to corrode the middle section of the stripped section of the double-clad pump fiber coating layer, and the corrosion length is about 2 cm, so as to ensure that the taper waist diameter formed after the corrosion is about 230 μm.

[0074] 2) Primary bunching.

[0075] Figure 3 Fig. 2 is a schematic diagram of the structure of a seven-hole torsion clamp used in an embodiment. Six pretreated pump fibers and a hollow glass tube (the inner and outer diameters are 200 / 240 μm) are sequentially inserted into the through holes of the seven-hole torsion clamp, wherein the hollow glass tube is inserted into the through hole at the center, and then the six pump fibers and the hollow glass tube are correspondingly inserted into the through holes of another seven-hole torsion clamp, as shown in Fig. 3, wherein 31 represents the pump fiber, and 32 represents the hollow glass tube. Figure 4 The two seven-hole torsion clamps are twisted in opposite directions for several turns, the pump fibers and the hollow glass tube are tightly attached by the torsion, and the taper is formed after heating and drawing, as shown in Fig. 4. Figure 5 Figure 5 Fig. 5 is a schematic diagram of the primary bunching completed by twisting and knotting and heating and drawing in an embodiment. The diameter of the fiber bundle after the drawing needs to be consistent with the inner cladding diameter of the output signal fiber, so as to facilitate the fusion operation. In this embodiment, the taper waist diameter of the fiber bundle after the drawing is 400 μm, the taper length is 2 cm, and the waist length is 1.5 cm.

[0076] 3) Pretreatment of the input signal fiber;

[0077] ​The input signal fiber is a 25 / 400 μm (NA=0.06 / 0.46) double-clad fiber, and the input signal fiber 5 needs to be etched using pure hydrofluoric acid. The first end of the signal fiber 5 is stripped of a certain length of the signal fiber coating layer 51 to form a bare fiber segment 52. The free end of the bare fiber segment 52 of the signal fiber 5 is etched to form a taper-waist end. The taper-waist end includes a taper region 53 with a certain length and a waist region 54 with a certain length, and the waist region 54 is located at the outermost end. As shown in the figure Figure 6 The taper-waist end has a waist region length of about 2 cm, the taper region diameter of the taper-waist end is determined by the inner diameter of the hollow glass tube after tapering, and the taper region length of the taper-waist end is about 5 cm.

[0078] 4) The pre-processed signal fiber is inserted into the hollow glass tube in the primary bundled fiber bundle to complete the secondary bundled fiber bundle.

[0079] 5) The secondary bundled fiber bundle is subjected to re-bundling treatment to obtain a tertiary bundled fiber bundle.

[0080] Subsequently, the taper containing the input signal fiber and the pump fiber is heated and weakly tapered to ensure that the input signal fiber and the surrounding six pump fibers are fused tightly at high temperature, which facilitates subsequent fusion. The entire weak tapering process does not change the core size of the input signal fiber.

[0081] 6) The tertiary bundled fiber bundle is flatly cut and then fused with the output signal fiber to complete the preparation of the fiber end face pump-signal coupler.

[0082] Figure 7 The figure shows the structure of the taper end face after twisting. The output signal fiber 6 is also a 25 / 400 μm (NA=0.06 / 0.46) double-clad fiber. The output signal fiber 6 includes an output signal fiber coating layer 61 and an output signal fiber cladding layer 62.

[0083] First, the output signal fiber is stripped of the coating layer at one end using a middle section stripping machine to form a bare fiber segment. The bare fiber segment of the output signal fiber is wiped clean with acetone or alcohol solution to ensure that the fiber cladding is free of contaminants. The end of the output signal fiber is flatly cut using a cutting knife to ensure that the end length is about 2 cm and the end face quality is good.

[0084] The tertiary bundled fiber bundle is flatly cut, and the end of the tertiary bundled fiber bundle after cutting is flatly cut and retains a certain length of the waist region of the signal fiber. That is, the tertiary bundled fiber bundle is flatly cut from the waist region of the tertiary bundled fiber.

[0085] The flat cut three times group bundle fiber bundle is fused with the preprocessed output signal fiber by a fusion machine to complete the preparation of the fiber end face pump-signal coupler. Feedback alignment is used in the fusion process to ensure the core alignment of the input signal fiber and the output signal fiber in the fiber bundle, to reduce the insertion loss and the influence on the device spot characteristics. Figure 7 Fig. 2 is a structural schematic diagram of the fiber end face pump-signal coupler fused in an embodiment.

[0086] The input signal fiber and the output signal fiber of the end face pump / signal coupler in the embodiment are of the same type of fiber. Then, the etching proportion of the input fiber and the tapering proportion of the pump fiber are determined according to the inner cladding size of the output signal fiber. The inner cladding size of the etched signal fiber should be the same as the inner diameter size of the tapered hollow glass tube, to ensure the tightness of the subsequent fiber bundle grouping, and the size of the fiber bundle should be the same as the inner cladding size of the output signal fiber. The embodiment solves the problems of the traditional (6+1) x 1 pump coupler, such as the increase of transmission loss and mode degradation caused by the mismatch of the core mode field between the input fiber and the output signal fiber due to the tapering of the input fiber, and can realize the high-quality preparation of the pump / signal coupler with any type of fiber.

[0087] 7) Coupler packaging.

[0088] Figure 8 Fig. 7 is a structural schematic diagram of the glass clamp provided in an embodiment for packaging the fiber end face pump-signal coupler. The fused fiber end face pump-signal coupler is fixed in the semicylindrical glass tank 71 by ultraviolet curing glue, and low refractive index ultraviolet glue is coated at the stripped coating layer of the output signal fiber to reduce the temperature rise at this position. Then, the semicylindrical glass tank 71 is inserted into the cylindrical glass tube 72 together with the coupler, and the two ports of the cylindrical glass tube 72 are sealed with high refractive index ultraviolet glue.

[0089] In summary, in view of the problems of excessive signal light transmission loss, mode degeneration, excessive output signal fiber temperature rise caused by pump light and unstable operation in vacuum and vibration environment in the traditional (N+1) x 1 type end-pumped / signal coupling device manufacturing scheme, the application proposes a preparation method of an optical fiber end-pumped-signal coupling device based on a twisting method. In this method, the signal fiber is not subjected to tapering, but the signal fiber and the pump fiber are bundled by means of a self-designed hollow glass tube. The first advantage of this treatment is that the central signal fiber does not participate in the twisting and tapering process, effectively eliminating the influence of the twisting stress on the signal light transmission quality. The second advantage is that the (N+1) x 1 type optical fiber end-pumped / signal coupling device can be manufactured according to the size of the output signal fiber, improving the practicability of the coupling device. In addition, by etching the cladding of the pump fiber to reduce the tapering ratio, the temperature characteristics of the coupling device under high-power operation can be improved, providing a guarantee for realizing higher-power and higher-beam-quality fiber laser systems. When the coupling device is applied to backward pumping, in order to prevent damage to the pump source and the coupling device caused by back light, the pump fiber is subjected to partial roughening treatment in the preparation scheme mentioned in the specification. In terms of packaging fixtures, the application specially designs a nested glass tube with good sealing performance as a packaging fixture, so that the coupling device can operate more stably in complex environments such as vacuum and vibration.

[0090] The remaining matters of the application are known technologies.

[0091] The technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the technical features in the above embodiments are not described, but as long as the combinations of the technical features do not exist contradictory, they should be considered as the scope of the specification.

[0092] The above-described embodiments only express several implementation manners of the application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for ordinary skilled persons in the art, without departing from the concept of the application, some modifications and improvements can be made, which are within the protection scope of the application. Therefore, the protection scope of the patent of the application should be subject to the appended claims.

[0093] The above-described embodiments only express several implementation manners of the application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for ordinary skilled persons in the art, without departing from the concept of the application, some modifications and improvements can be made, which are within the protection scope of the application. Therefore, the protection scope of the patent of the application should be subject to the appended claims. The above-described embodiments only express several implementation manners of the application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for ordinary skilled persons in the art, without departing from the concept of the application, some modifications and improvements can be made, which are within the protection scope of the application. Therefore, the protection scope of the patent of the application should be subject to the appended claims.

Claims

1. A method of making a fiber end-pumped signal coupler, characterized in that, The application relates to a method for preparing a fiber end-surface pump-signal coupler. The method comprises the following steps: pretreating pump fibers, and then twisting and knotting the pretreated pump fibers and a hollow glass tube to form a primary bundled fiber bundle, wherein the hollow glass tube is located at a center position of the primary bundled fiber bundle, and the pump fibers are tightly combined around the hollow glass tube at the periphery of the hollow glass tube; pretreating a signal fiber, including stripping a coating layer of a first end of the signal fiber to form a bare fiber segment, and etching a free end of the bare fiber segment to form a taper-waist end, wherein the taper-waist end comprises a taper region and a waist region, and the waist region is located at an outermost end; inserting the pretreated signal fiber into the hollow glass tube in the primary bundled fiber bundle to form a secondary bundled fiber bundle; performing a re-bundling treatment on the secondary bundled fiber bundle, including heating and weakly tapering the secondary bundled fiber bundle by using a heat source, and keeping the size of a fiber core of the input signal fiber unchanged during the whole weak tapering process, so that the signal fiber is fused with the hollow glass tube and the pump fibers to form a tertiary bundled fiber bundle; and performing a flat cutting on the tertiary bundled fiber bundle, and then fusing the tertiary bundled fiber bundle with an output signal fiber to complete the preparation of the fiber end-surface pump-signal coupler. The method comprises the following steps: pretreating the pump fibers, including stripping a coating layer of a middle segment of each pump fiber to form a bare fiber segment, etching the bare fiber segment by using a hydrofluoric acid solution to form an etching taper region, an etching waist region and an etching roughened part, and then performing a primary bundling on the pretreated pump fibers. The method comprises the following steps: Two multi-hole twist clamps are prepared, and the two multi-hole twist clamps are oppositely arranged, wherein the multi-hole twist clamp comprises a clamp body, and a plurality of through holes are arranged on the clamp body, wherein one through hole is a center hole, and the remaining through holes are uniformly distributed in a ring shape around the periphery of the center hole; 2. The method of claim 1, wherein the step of forming the optical fiber end face pump-signal coupler is performed by a process comprising: A hollow glass tube is prepared, the hollow glass tube is inserted into the center hole of the two multi-hole twist clamps, and the pretreated pump fibers are inserted into the through holes around the periphery of the center hole of the two multi-hole twist clamps one by one; ​ 3. A method of making a fiber end-pumped-signal coupler as claimed in claim 1 or claim 2, wherein, The pump fibers and the hollow glass tube are tightly combined by twisting the multi-hole twist clamps; The twisted fiber bundle is heated and tapered to form a taper region, and the primary bundling is completed to obtain a primary bundled fiber bundle. The outer diameter of the taper region of the primary bundled fiber bundle is consistent with the outer diameter of the inner cladding of the output signal fiber. The taper-waist end of the pretreated signal fiber is inserted into the hollow glass tube in the primary bundled fiber bundle to form a secondary bundled fiber bundle. The tertiary bundled fiber bundle is flatly cut and then fused with the output signal fiber, including the following steps:

4. The method of claim 3, wherein the step of forming the optical fiber end face pump-signal coupler is performed by a process comprising: The tertiary bundled fiber bundle is flatly cut, and the end of the tertiary bundled fiber bundle is required to be flatly cut and to retain a certain length of the waist region of the signal fiber after the cutting; ​ 5. The method of claim 1 to 4, wherein: The output signal fiber is pretreated, a bare fiber segment is formed by stripping a coating layer of one end of the output signal fiber, and the end of the bare fiber segment of the output signal fiber is flatly cut.

6. The method of claim 5, wherein the step of forming the optical fiber end face pump-signal coupler is performed by the steps of: ​ ​ ​ ​ The three times group bundle optical fiber bundle after flat cutting is fused with output signal optical fiber by using a fusion machine to complete the preparation of the fiber end face pump-signal coupler.

7. The method of claim 6, wherein the step of forming the optical fiber end face pump-signal coupler is performed by the steps of: providing a first optical fiber having a first end face; providing a second optical fiber having a second end face; and joining the first and second optical fibers together to form the optical fiber end face pump-signal coupler. The prepared fiber end face pump-signal coupler is packaged in a glass clamp. 8.The fiber end face pump-signal coupler prepared by the preparation method of the fiber end face pump-signal coupler according to claim 1.

9. A fiber laser characterized by, The preparation method comprises the following steps: preparing a seed laser and a plurality of pump lasers, and coupling and connecting the seed laser and the plurality of pump lasers through the fiber end face pump-signal coupler prepared by the preparation method of the fiber end face pump-signal coupler according to claim 1.

Images