Cladding light filtering structure and manufacturing method of triple-clad optical fiber

Abstract

A cladding light filtering structure and manufacturing method of a triple-clad optical fiber, comprising an upper cover and an optical fiber base, wherein the base comprises a front stray light filtering structure, a mode scrambling structure, and a rear stray light filtering structure, wherein the mode scrambling structure has a jump notch and is located in the middle of the optical fiber base, wherein the mode scrambling optical fiber is wound in the wire groove of the mode scrambling structure, wherein one end of the front stray light filtering structure is connected to one end of the mode scrambling optical fiber of the inner circle of the mode scrambling structure and is fixed on the optical fiber base, and the optical fiber of the other end extends out of the front of the optical fiber base, wherein one end of the rear stray light filtering structure is connected to one end of the mode scrambling optical fiber of the outer circle of the mode scrambling structure and is fixed on the optical fiber base, and the optical fiber of the other end extends out of the rear of the optical fiber base, and the upper cover covers and is fixed on the optical fiber base. The present invention has a simple structure and good filtering effect, and can achieve controllable output beam quality while ensuring the mechanical properties of the optical fiber.

Description

[0001] This invention is a divisional application of the invention patent entitled “Cladding light filtering structure and manufacturing method of triple-clad optical fiber” with application number 202210073128.5 filed on January 21, 2022. Technical Field

[0002] The invention belongs to the field of laser technology, and in particular relates to a cladding light filtering structure of a triple-cladding optical fiber and a preparation method thereof. Background Art

[0003] With the development of laser technology, the output power of fiber lasers continues to increase, and the pressure on various devices on the fiber link increases accordingly. Filtering out unnecessary cladding light can effectively reduce the heat caused by absorption of the fiber coating layer, reduce the "stray light" with a large divergence angle after the laser spatial output, and increase the reliability of the entire laser link. In addition, during the normal operation or application of the laser, part of the laser will be reflected back along the original path to act on the core components inside the laser. When the intensity of the return light reaches a certain threshold, it will cause the internal components of the laser to operate unstably or be irreversibly damaged.

[0004] In order to reduce the loss, the energy transmission fiber of high-power fiber laser usually adopts a three-cladding structure, in which the core and outer cladding are pure silica layers, and the inner cladding is a fluorine-doped low refractive index layer. The ideal refractive index distribution of the energy transmission fiber is a complete "step type", and the refractive index distribution of the low refractive index layer should also be very flat. However, in actual use, this type of optical fiber is made by the MCVD or PCVD multi-layer deposition process. This process causes the refractive index distribution of the fluorine-doped layer of the inner cladding to be uneven in the radial and axial directions, which makes some of the "stray light" with a large divergence angle in the core transmission (usually including signal light and unabsorbed pump laser) enter the fluorine-doped layer and cannot further enter the outer cladding. This type of "stray light" is directly transmitted in the fluorine-doped layer. The current cladding mode filtering solution is basically to roughen or coat the surface of the optical fiber with a high refractive index material to export the outer cladding light, so it can only filter out the "stray light" of the outer cladding, and cannot remove the "stray light" transmitted by the fluorine-doped inner cladding. Such optical fibers include Nufern's BD-S100 / 120 / 360-STN, BD-S150 / 170 / 360-STN, BD-S200 / 230 / 660-STN, BD-S600 / 660 / 720-STN, etc. In optical fibers of this structure, the ratio of the core to the outer diameter is often small, and the thickness of the fluorine-doped layer is often thin. If the current industry-wide technical solutions are continued to be used, it is necessary to first remove the outer cladding of the entire optical fiber using physical or chemical methods, and then perform cladding light treatment after the internal fluorine-doped cladding is exposed. There are several problems with such treatment: First, the outer cladding of the optical fiber is generally thick, which makes it very difficult to remove and the efficiency is too slow. Second, since the inner cladding is very thin, the removal process can easily damage the waveguide structure of the inner cladding. Finally, the diameter of the treated optical fiber is very thin, and the treatment process will leave microcracks on the surface of the optical fiber, which will significantly reduce the mechanical properties of the optical fiber, causing certain risks in actual use. Summary of the invention

[0005] In order to solve the above problems, the present invention proposes a cladding light filtering structure and preparation method of a triple-cladding optical fiber. The light filtering structure has a simple structure and good filtering effect, and can control the output beam quality while ensuring the mechanical properties of the optical fiber.

[0006] The technical solution of the present invention is as follows:

[0007] A cladding light filtering structure for a triple-clad optical fiber is characterized in that it comprises an upper cover and an optical fiber base, wherein the base comprises a front stray light filtering structure, a mode scrambling structure, and a rear stray light filtering structure, wherein the mode scrambling structure has a jump notch and is located in the middle of the optical fiber base, wherein the mode scrambling optical fiber is wound in the wire groove of the mode scrambling structure, wherein one end of the front stray light filtering structure is connected to one end of the mode scrambling optical fiber of the inner circle of the mode scrambling structure and is fixed on the optical fiber base, and the optical fiber of the other end extends out of the front of the optical fiber base, wherein one end of the rear stray light filtering structure is connected to one end of the mode scrambling optical fiber of the outer circle of the mode scrambling structure and is fixed on the optical fiber base, and the optical fiber of the other end extends out of the rear of the optical fiber base, and wherein the upper cover covers and is fixed on the optical fiber base.

[0008] The core and outer cladding of the triple-clad optical fiber are pure silicon dioxide layers, the inner cladding is a fluorine-doped low-refractive index layer, and the numerical aperture is NA0.12-0.24.

[0009] The optical fiber base is a semicircular long shell with a certain diameter. The cross-sectional diameter of the optical fiber base ranges from 1 to 8 cm. The bending surface angle ranges from 90 to 180 degrees. The optical fiber base may be a wave structure formed by combining multiple curved surfaces.

[0010] The method for manufacturing the cladding light filtering structure of the triple-cladding optical fiber comprises the following steps:

[0011] 1) The outer cladding of the optical fiber is processed by chemical corrosion, laser or mechanical etching, the processing range includes physical size and surface structure, and the processed part is sealed with a capillary;

[0012] 2) Perform software simulation calculations based on the actual refractive index distribution of the fluorine-doped layer and the test results of the beam quality input at the input end, and select the diameter of the fiber scrambling mode of the scrambling mode structure and the number of turns of the fiber scrambling mode based on the calculation results;

[0013] 3) Use mechanical stress to bend a piece of metal into a three-dimensional disturbed mode structure, or a semicircular long shell of a certain diameter, etch a circular or square U-shaped groove on the metal surface, and coil the processed optical fiber through the U-shaped groove. The optical fiber winding can be adjusted by jumping the notch: 1.3 to 10 cm, and the number of optical fiber winding turns can be selected: 2 to 15 turns, and the heat-conductive silicone grease is used to flatten and fix it.

[0014] 4) A surface heat dissipation grille is made on the upper cover;

[0015] 5) According to the simulation calculation result of step 1), the positions of the front stray light filtering structure and the rear stray light filtering structure are determined;

[0016] 6) The front stray light filtering structure is connected to one end of the optical fiber of the inner circle of the mode scrambling structure and fixed to the optical fiber base, and the optical fiber at the other end extends out of the front of the optical fiber base; one end of the rear stray light filtering structure is connected to one end of the optical fiber of the outer circle of the mode scrambling structure and fixed to the optical fiber base, and the optical fiber at the other end extends out of the back of the optical fiber base;

[0017] 7) Cover the upper cover on the optical fiber base and fix it with screws.

[0018] The technical effects of the present invention are as follows:

[0019] The outer cladding of the optical fiber is processed by chemical corrosion, laser or mechanical etching, and the processing range includes physical size and surface structure, and the capillary is used to seal the processed part. The "stray light" with large divergence angles before and after the mode is disturbed is filtered out; the "stray light" with large divergence angles mainly includes the forward transmission stray light of the laser equipment and the backward reflected light;

[0020] The mechanical stress bending three-dimensional mode scrambling structure or the spatial circular body (fixed diameter) winding is adopted to control the bending strength of the fiber winding through its precise fiber winding mechanism, causing the macro bending of the fiber. This will significantly increase the coupling between modes and the coupling of "stray light" with large divergence angle to the radiation mode, further improving the filtering efficiency of stray light.

[0021] The function of the upper cover structure is to fix the optical fiber and dissipate heat on the surface;

[0022] Fiber coiling base structure: cross-sectional diameter range: 1 to 8 cm; bending surface angle range: 90 to 180°; multiple curved surfaces can be combined to form a wave structure;

[0023] Structural function: High-power heat dissipation requirements can be achieved through water cooling on the solid base;

[0024] All the above structures are made or installed on the optical fiber winding base to finally form the present invention.

[0025] 5. Triple-clad optical fiber structure description:

[0026] The fiber core A and the outer cladding C are pure silica layers, the inner cladding B is a fluorine-doped low refractive index layer, and the numerical aperture NA ranges from 0.12 to 0.24.

[0027] The present invention causes macrobending of triple-clad optical fiber by external force winding, thereby increasing coupling between modes and coupling of "stray light" with a large divergence angle to the radiation mode. The radiation mode is transmitted from the core into the cladding and then filtered out by a post-stray light filtering mechanism.

[0028] Technical Effects of the Invention

[0029] 1. Achieve efficient filtering of cladding light in a bidirectional and stable manner for triple-clad optical fiber;

[0030] 2. Realize adjustable output energy distribution and beam quality of triple-clad fiber laser;

[0031] 3. Realize high-power filtering and stable heat dissipation of triple-clad optical fiber cladding light; BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the overall structure of the cladding light filtering structure of the triple-cladding optical fiber of the present invention;

[0033] Figure 2 This is a schematic diagram of the structure of the optical fiber disk mode scrambling base 2 of the present invention;

[0034] Figure 3 It is a left side view of the present invention;

[0035] Figure 4 The refractive index design distribution of the triple-clad optical fiber of the present invention is;

[0036] Figure 5 The refractive index test distribution of the triple-clad optical fiber of the present invention; DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with embodiments and drawings, but the protection scope of the present invention shall not be limited thereto.

[0038] See also Figure 1 , Figure 2 , Figure 3 As can be seen from the figure, the cladding light filtering structure of the triple-clad optical fiber of the present invention comprises an upper cover 1 and an optical fiber base 2, wherein the base 2 comprises a front stray light filtering structure 2.1, a mode scrambling structure 2.2, and a rear stray light filtering structure 2.3, wherein the mode scrambling structure 2.2 has a jump notch 2.21, which is located in the middle of the optical fiber base 2, and a mode scrambling optical fiber is wound in the wire groove of the mode scrambling structure 2.2, wherein one end of the front stray light filtering structure 2.1 is connected to one end of the mode scrambling optical fiber of the inner circle of the mode scrambling structure 2.2 and is fixed on the optical fiber base 2, and the optical fiber at the other end extends out of the front of the optical fiber base 2, wherein one end of the rear stray light filtering structure 2.3 is connected to one end of the mode scrambling optical fiber of the outer circle of the mode scrambling structure 2.2 and is fixed on the optical fiber base 2, and the optical fiber at the other end extends out of the rear of the optical fiber base 2, and the upper cover 1 covers and is fixed on the optical fiber base 2.

[0039] The method for manufacturing the cladding light filtering structure of the triple-cladding optical fiber comprises the following steps:

[0040] 1) The outer cladding of the optical fiber is processed by chemical corrosion, laser or mechanical etching, the processing range includes physical size and surface structure, and the processed part is sealed with a capillary;

[0041] 2) Perform software simulation calculations based on the actual refractive index distribution of the fluorine-doped layer and the test results of the beam quality input at the input end, and select the diameter of the fiber scrambling mode of the scrambling mode structure 2.2 and the number of turns of the fiber winding based on the calculation results;

[0042] 3) A piece of metal is bent into a three-dimensional disturbed mode structure or a semicircular long shell of a certain diameter by mechanical stress, and a circular or square U-shaped wire groove is etched on the metal surface, and the processed optical fiber is coiled through the U-shaped wire groove, wherein the optical fiber coiling can be adjusted by the jump notch 2.21 to achieve an adjustable optical fiber coiling diameter of 1.3 to 10 cm, and the number of optical fiber coiling turns can be selected from 2 to 15 turns, and the heat conductive silicone grease is used to flatten and fix, and a surface heat dissipation grille is made on the upper cover 1;

[0043] 4) A surface heat dissipation grille is made on the upper cover;

[0044] 5) According to the simulation calculation results of step 1), the positions of the front stray light filtering structure 2.1 and the rear stray light filtering structure 2.3 are determined;

[0045] 6) The front stray light filtering structure 2.1 is connected to one end of the inner optical fiber of the mode scrambling structure 2.2 and fixed to the optical fiber base 2, and the optical fiber at the other end extends out of the front of the optical fiber base 2; one end of the rear stray light filtering structure 2.3 is connected to one end of the outer optical fiber of the mode scrambling structure 2.2 and fixed to the optical fiber base 2, and the optical fiber at the other end extends out of the back of the optical fiber base 2;

[0046] 7) Cover the upper cover 1 on the optical fiber base 2 and fix it with screws.

[0047] See also Figure 3 , Figure 4 , Figure 4 The refractive index design distribution of the triple-clad optical fiber of the present invention is; Figure 5 The test distribution of the refractive index of the triple-clad optical fiber of the present invention is shown in the experiment. The present invention has the characteristics of simple structure and good filtering effect, and can control the output beam quality while ensuring the mechanical properties of the optical fiber.

Claims

1. An inner cladding light filtering structure of a multi-clad optical fiber, characterized in that The optical fiber base (2) comprises an upper cover (1) and an optical fiber base (2), wherein the optical fiber base (2) comprises a front stray light filtering structure (2.1), a mode scrambling structure (2.2), and a rear stray light filtering structure (2.3), wherein a mode scrambling optical fiber is wound in a line groove of the mode scrambling structure (2.2), wherein the mode scrambling optical fiber is a multi-clad optical fiber, comprising a core, an inner cladding, and an outer cladding, wherein one end of the front stray light filtering structure (2.1) is connected to one end of the mode scrambling optical fiber and is fixed to the optical fiber base (2), and one end of the rear stray light filtering structure (2.3) is connected to the other end of the mode scrambling optical fiber and is fixed to the optical fiber base (2), and the upper cover (1) covers and is fixed to the mode scrambling optical fiber; The optical fiber base (2) is a heat-conducting material, which is bent into a three-dimensional mode-scrambling structure by mechanical stress. By controlling the bending strength of the optical fiber winding, macrobending of the mode-scrambling optical fiber is caused to guide the stray light transmitted in the inner cladding into the outer cladding.

2. The inner cladding light filtering structure of a multi-clad optical fiber according to claim 1, characterized in that The core (A) and outer cladding (C) of the multi-clad optical fiber are pure silica layers, the inner cladding (B) is a fluorine-doped low refractive index layer, and the numerical aperture NA ranges from 0.12 to 0.

24.

3. The inner cladding light filtering structure of a multi-clad optical fiber according to claim 1 or 2, characterized in that: By means of mechanical stress bending, the optical fiber base (2) is formed into a semicircular long shell with a certain diameter, the cross-sectional diameter of the optical fiber base (2) can be varied within a range of 1 to 8 cm, the bending surface angle can be varied within a range of 90 to 180°, or the optical fiber base (2) can be formed into a wave structure composed of multiple curved surfaces.

4. The inner cladding light filtering structure of a multi-clad optical fiber according to claim 1 or 2, characterized in that: The mode scrambling structure (2.2) has a jump notch (2.21) located in the middle of the optical fiber base (2).

5. The inner cladding light filtering structure of a multi-clad optical fiber according to claim 4, wherein the optical fiber is coiled through the jump notch (2.21) to achieve an adjustable range of optical fiber coiling diameter of 1.3 to 10 cm, and the number of optical fiber coiling turns is optional in the range of 2 to 15 turns, and is flattened and fixed in the wire groove using thermal conductive silicone grease.

6. A method for manufacturing an inner cladding light filtering structure of a multi-clad optical fiber, wherein the inner cladding light filtering structure of the multi-clad optical fiber comprises an upper cover (1) and an optical fiber base (2), the optical fiber base (2) comprises a front stray light filtering structure (2.1), a mode scrambling structure (2.2), and a rear stray light filtering structure (2.3), and a mode scrambling optical fiber is wound in a line groove of the mode scrambling structure (2.2), and the method is characterized by comprising the following steps: 1) The outer cladding of the optical fiber is processed by etching, and the processed part is sealed by a capillary; 2) The inner cladding is a fluorine-doped layer, and software simulation calculation is performed according to the actual refractive index distribution of the fluorine-doped layer and the test results of the beam quality input from the input end, and the diameter of the scrambled mode fiber of the scrambled mode structure (2.2) and the number of turns of the optical fiber are selected based on the calculation results; 3) using mechanical stress to bend a piece of heat-conducting material into a three-dimensional optical fiber base (2), etching a groove on the surface of the heat-conducting material, winding the treated optical fiber through the groove, and controlling the bending strength of the optical fiber winding to cause macrobending of the optical fiber, so as to guide the stray light transmitted in the inner cladding into the outer cladding; 4) Making a surface heat dissipation grille on the upper cover; 5) According to the simulation calculation results of step 2), the positions of the front stray light filtering structure (2.1) and the rear stray light filtering structure (2.3) are determined; 6) connecting the front stray light filtering structure (2.1) to one end of the optical fiber of the mode scrambling structure (2.2) and fixing them on the optical fiber base (2); connecting one end of the rear stray light filtering structure (2.3) to the other end of the optical fiber of the mode scrambling structure (2.2) and fixing them on the optical fiber base (2); 7) Covering the upper cover (1) on the optical fiber base (2) and fixing it.

7. The method for manufacturing the inner cladding light filtering structure of a multi-clad optical fiber according to claim 6, characterized in that The core (A) and outer cladding (C) of the multi-clad optical fiber are pure silica layers, and the numerical aperture NA ranges from 0.12 to 0.

24.

8. The method for manufacturing the inner cladding light filtering structure of a multi-clad optical fiber according to claim 6 or 7, characterized in that: By means of mechanical stress bending, the optical fiber base (2) is formed into a semicircular long shell with a certain diameter, the cross-sectional diameter of the optical fiber base (2) can be varied within a range of 1 to 8 cm, the bending surface angle can be varied within a range of 90 to 180°, or the optical fiber base (2) can be formed into a wave structure composed of multiple curved surfaces.

9. The method for manufacturing the inner cladding light filtering structure of a multi-clad optical fiber according to claim 6 or 7, characterized in that: The mode scrambling structure (2.2) has a jump notch (2.21) located in the middle of the optical fiber base (2).

10. The method for manufacturing the inner cladding light filtering structure of a multi-clad optical fiber according to claim 9, wherein the optical fiber is coiled through the jump notch (2.21) to achieve an adjustable range of optical fiber coiling diameter of 1.3 to 10 cm, and the number of optical fiber coiling turns is optional in the range of 2 to 15 turns, and is flattened and fixed in the wire groove using thermal conductive silicone grease.

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