阅读说明：本技术 一种双包层有源光纤及其制备方法 (Double-clad active optical fiber and preparation method thereof ) 是由 周震华 徐律 宋海瑞 冯术娟 缪振华 侯树虎 卞新海 韩婷婷 赵霞 于 2021-08-11 设计创作，主要内容包括：本发明涉及一种双包层有源光纤,其截面结构由内向外依次为纤芯、包层、内涂层、外涂层,所述包层内设置有四个填充区域,四个填充区域对称设置在所述纤芯两侧,所述内涂层为低折射率内涂层,所述外涂层为丙烯酸树脂高模量外涂层,所述纤芯相对包层的折射率差Δ1为0.0010-0.0015,所述填充区域相对包层的折射率差Δ2为-0.0080～-0.0120。本发明四个填充区域的引入可抑制了螺旋光的形成和传输,增大包层泵浦吸收,且四个填充区域的引入属于一次成型,步骤简单可实施性强,且成本低,对于批量化生产具备优势。且内包层可设计为圆形,大大提高了有源光纤与无源光纤的匹配性和相容性,以及有源光纤制备过程中的几何控制精度,从而降低熔接损耗。(The invention relates to a double-cladding active optical fiber, which is characterized in that the cross-sectional structure of the double-cladding active optical fiber sequentially comprises a fiber core, a cladding, an inner coating and an outer coating from inside to outside, wherein four filling areas are arranged in the cladding, the four filling areas are symmetrically arranged on two sides of the fiber core, the inner coating is a low-refractive-index inner coating, the outer coating is an acrylic resin high-modulus outer coating, the refractive index difference delta 1 of the fiber core relative to the cladding is 0.0010-0.0015, and the refractive index difference delta 2 of the filling areas relative to the cladding is-0.0080-0.0120. The four filling regions are introduced, so that the formation and transmission of spiral rotation can be inhibited, the absorption of the cladding pump is increased, the four filling regions are introduced in one-step forming, the steps are simple, the practicability is high, the cost is low, and the method has the advantages of mass production. And the inner cladding can be designed into a round shape, so that the matching and compatibility of the active optical fiber and the passive optical fiber are greatly improved, and the geometric control precision in the preparation process of the active optical fiber is improved, thereby reducing the fusion loss.)

1. The utility model provides a double-clad active optical fiber, its cross sectional structure is fibre core (1), cladding (2), undercoating (4), overcoating (5) from inside to outside in proper order, its characterized in that: the novel optical fiber core is characterized in that four filling areas (3) are arranged in the cladding (2), the four filling areas (3) are symmetrically arranged at the upper, lower, left and right positions of the fiber core (1), the modulus of the inner coating (4) is smaller than that of the outer coating (5), the refractive index difference delta 1 of the fiber core (1) relative to the cladding (2) is 0.0010-0.0015, and the refractive index difference delta 2 of the stress area (3) relative to the cladding (2) is-0.0080-0.0120.

2. The double-clad active optical fiber of claim 1, wherein: diameter D of the core (1)₁20 to 30 μm, the diameter D of the cladding (2)₂400 to 450 [ mu ] m, the diameter D of the inner coating (4)₃450 to 510 mu m, and the diameter D of the outer coating₄530 to 580 μm, length L of single filling region₁10 to 15 μm in width L₂5 to 7 μm, and the center-to-center distance D between the two symmetrical filling regions (3) is 150 to 200 μm.

3. The double-clad active optical fiber of claim 2, wherein: the main component of the fiber core is pure quartz and comprises the following dopants in mol percent:

Yb₂O₃：0.3~0.6，

Al₂O₃：1~6，

P₂O₅：1~5，

SiF₄：0.1~0.5，

PbO₂：0~0.5；

the material of the cladding (2) is pure quartz;

the main component of the filling area (3) is pure quartz and comprises the following dopants in mol percent:

GeO2：0.1～2，

B₂O₃：20～35。

4. the double-clad active optical fiber of claim 1, wherein: the modulus of the inner coating (4) is less than 1MPa and the modulus of the outer coating is greater than 1 KMPa.

5. A method of making the double-clad active optical fiber of any one of claims 1-4, wherein: the method comprises the following steps:

the method comprises the following steps: pretreating the base tube to eliminate impurities and bubbles on the inner wall of the base tube;

step two: depositing on the inner wall of the base tube, wherein the depositing process comprises pure silicon cladding deposition, filling area deposition and pure silicon cladding deposition in sequence;

after deposition in a filling area is finished, performing directional etching on an annular filling ring obtained by deposition, wherein a base pipe does not rotate any more, introducing corrosive gas into the base pipe, heating two walls of the base pipe by moving two fire sources outside the base pipe back and forth along the axial direction of the base pipe, corroding the heating part of the annular filling area by the corrosive gas to be gradually etched, wherein two fire heads are always symmetrical outside the base pipe, the number of times of moving the fire heads back and forth is the etching times, the etching times are controlled to be 15-20 times, and the base pipe is turned over for 180 ℃ each time to ensure the etching consistency of the two walls of the stress ring until the two walls are completely etched to obtain two completely separated crescent filling area; turning the base pipe by 90 degrees, and repeating the operation until the two walls are completely cut through to obtain another two completely separated crescent filling area areas;

after the etching of the filling area is finished, depositing a pure silicon cladding on the inner ring of the filling area;

step three: continuing to deposit the silica loose body on the inner surface of the substrate tube in the second step, cutting off the tail tube of the substrate tube after the deposition is finished, and then immersing the substrate tube into the substrate tube containing YbCl₃，AlCl₃，H₃PO₄In solution of (2), wherein YbCl₃The molar concentration is 0.01-0.5%, and AlCl is added₃Molar concentration of 0.01-1.0%, H₃PO₄The molar concentration is 0.1-1%, and the silicon dioxide loose body is doped in a solution soaking mode;

step four: taking out the blow-dried base pipe from the solution in the third step, connecting a tail pipe again, then carrying out oxidation drying and vitrification on the loose silica body in the base pipe, and finally collapsing into a solid rod;

step five: polishing the surface of the solid rod, and fusing and shrinking the sleeve into a whole to obtain an optical fiber preform;

step six: and (3) thinning the optical fiber preform into a quartz optical fiber, coating and curing the low-refractive-index coating inner coating and the acrylic resin optical fiber coating outer coating outside the quartz optical fiber in sequence, and preparing the double-cladding active optical fiber.

6. The method of claim 5, wherein the step of preparing the double-clad active optical fiber comprises: the deposition temperature of the initial pure silicon cladding is 1900-2200 ℃, and the deposition temperature of SiCl is₄The deposition flow is 20-300 sccm, the deposition speed is 10-100 mm/min, and the number of deposition layers is 2-5;

the deposition temperature of the filling region is 1700-1900 ℃, and SiO is₂Flow rate: 200-300sccm, GeCl₄Flow rate: 50-100sccm, BCl₃Flow rate: 800-;

the deposition temperature of the pure silicon cladding is 1900-2200 ℃, and the deposition temperature of SiCl is₄The deposition flow is 20-300 sccm, the deposition speed is 50-100 mm/min, and the number of deposition layers is 2-10.

7. The method of claim 5, wherein the step of preparing the double-clad active optical fiber comprises: in the third step, the deposition temperature of the silicon dioxide loose body is 1300-1700 ℃, and SiCl is adopted₄The deposition flow rate is 100-400 sccm.

8. The method of claim 5, wherein the step of preparing the double-clad active optical fiber comprises: and step four, oxidizing the doped elements of the silicon dioxide loose body by oxygen, and drying the loose body by chlorine.

Technical Field

The invention relates to a double-clad active optical fiber and a manufacturing method thereof. Belongs to the technical field of optical fibers.

Background

The fiber laser has the remarkable advantages of small volume, good heat dissipation, high stability, good beam quality, high skew efficiency and the like, gradually becomes the leading strength in the laser industry, is always concerned by scholars and engineering technicians in the field, and is widely applied to the aspects of industrial processing, weaponry, medical appliances and the like at present. The large-mode-field double-cladding ytterbium-doped active fiber serving as the most important component in the ytterbium-doped active fiber laser is important to the performance of the fiber laser in the design of the structure and the components.

The absorption coefficient is an important index in the performance of the ytterbium-doped active optical fiber, the length of the ytterbium-doped active optical fiber in the optical fiber laser is determined by the height of the absorption coefficient, the actual use length of the active optical fiber can be increased by the low absorption coefficient, the serious nonlinear effect of the laser under high power is caused, and the fiber skew efficiency is reduced. And relatively, the higher absorption coefficient can effectively reduce the use length of the ytterbium-doped optical fiber and improve the output efficiency of the laser.

The cladding absorption coefficient of the existing ytterbium-doped active optical fiber is improved mainly by two methods, and one method is to improve the cladding absorption coefficient by improving the concentration of doped ytterbium ions, but the optical fiber is obviously photodarkened by the method. Therefore, how to increase the cladding pumping absorption while keeping the doping concentration of the core unchanged has become a problem to be solved. The other method is to change the geometric structure of the inner cladding of the quartz glass, and process the outer quartz glass into D-shaped or octagonal by a mechanical processing method so as to reduce the transmission of cladding pumping light in a spiral rotation mode, improve the probability of the pumping light passing through the core layer and achieve the purpose of improving the absorption of the cladding layer. The octagonal double-cladding active optical fiber is the mainstream optical fiber design for manufacturing a high-power optical fiber laser at present.

In order to reduce the spiral rotation and improve the absorption of cladding pumping, the conventional double-cladding active fiber adopts a special-shaped cladding design, so that the active fiber and the passive fiber are difficult to weld, additional eccentricity is easy to introduce by machining, the welding loss can be increased, and the beam quality is reduced. In addition, the geometric dimension control of the profiled optical fiber during drawing is difficult.

Chinese patent 201710225014.7 has invented a circular double-clad active optical fiber, be provided with a plurality of filling regions in the inner cladding, and the refracting index of filler is less than the refracting index of inner cladding, the effective waveguide area of cladding has been reduced, the formation and the transmission of spirorotation have been suppressed greatly, the speed of fibre core is passed to the cladding light of improvement, increase cladding pumping is absorbed, because the suppression of spirorotation no longer needs the optic fibre appearance of non-circle, make circular active optical fiber become possible, active optical fiber and passive optical fiber's matching nature and compatibility have been improved greatly, and the geometric control precision in the active optical fiber preparation process, thereby reduce the butt fusion loss, increase the efficiency and the reliability of laser. However, the introduction of a plurality of filling regions in the method is not one-time molding, a plurality of preforms with refractive indexes lower than that of the inner cladding layer need to be prepared, and the mother rod needs to be perforated for a plurality of times.

Disclosure of Invention

The technical problem to be solved by the present invention is to provide a double-clad active optical fiber in view of the above prior art, wherein four filling regions are disposed in the inner cladding, and the refractive index of the filler is lower than that of the inner cladding, so that the formation and transmission of the helical rotation can be suppressed, the pumping absorption of the cladding can be increased, and the introduction of the four filling regions belongs to one-step molding, and the double-clad active optical fiber has the advantages of simple steps, strong practicability, low cost, and mass production. Due to the fact that the four filling regions are introduced, spiral light can be restrained, the inner cladding can be designed to be circular, matching performance and compatibility of the active optical fiber and the passive optical fiber are greatly improved, geometric control precision in the active optical fiber preparation process is improved, and accordingly fusion loss is reduced.

The technical scheme adopted by the invention for solving the problems is as follows: the cross section structure of the double-cladding active optical fiber sequentially comprises a fiber core, a cladding, an inner coating and an outer coating from inside to outside, wherein four filling areas are arranged in the cladding, the four filling areas are symmetrically arranged at the upper, lower, left and right positions of the fiber core, the modulus of the inner coating is smaller than that of the outer coating, the refractive index difference delta 1 of the fiber core relative to the cladding is 0.0010-0.0015, and the refractive index difference delta 2 of stress areas of the four filling areas relative to the cladding is-0.0080-0.0120.

Preferably, the diameter D of the core₁20 to 30 μm, the diameter D of the cladding₂400 to 450 μm, the diameter D of the inner coating₃450 to 510 mu m, and the diameter D of the outer coating₄530 to 580 μm, length L of single filling region₁10 to 15 μm in width L₂5 to 7 μm, and the center-to-center distance D between the two filling regions is 150 to 200 μm.

Preferably, the main component of the core is pure quartz and comprises the following dopants in mol percent:

Yb₂O₃：0.3～0.6，

Al₂O₃：1～6，

P₂O₅：1～5，

SiF₄：0.1～0.5，

PbO₂：0～0.5；

preferably, the material of the cladding is pure quartz;

preferably, the main component of the filling area is pure quartz and comprises the following dopants in mol percent:

GeO2：0.1～2，

B₂O₃：20～35。

preferably, the modulus of the inner coating is less than 1MPa and the modulus of the outer coating is greater than 1 kMPa.

The preparation method of the double-cladding active optical fiber comprises the following steps:

the method comprises the following steps: pretreating (heating) the base tube to eliminate impurities and bubbles on the inner wall of the base tube;

step two: depositing on the inner wall of the base tube, wherein the depositing process comprises pure silicon cladding deposition, filling area deposition and pure silicon cladding deposition in sequence;

after deposition in a filling area is finished, performing directional etching on an annular filling ring obtained by deposition, wherein a base pipe does not rotate any more, introducing corrosive gas into the base pipe, heating two walls of the base pipe by moving two fire sources outside the base pipe back and forth along the axial direction of the base pipe, corroding the heating part of the annular filling area by the corrosive gas to be gradually etched, wherein two fire heads are always symmetrical outside the base pipe, the number of times of moving the fire heads back and forth is the etching times, the etching times are controlled to be 15-20 times, and the base pipe is turned over for 180 ℃ each time to ensure the etching consistency of the two walls of the stress ring until the two walls are completely etched to obtain two completely separated crescent filling area; the base tube is turned 90 degrees and the above operation is repeated until the two walls are completely cut through to obtain two other completely separated crescent-shaped filling area regions.

After the etching of the filling area is finished, depositing a pure silicon cladding on the inner ring of the filling area;

step three: continuing to deposit the silica loose body on the inner surface of the substrate tube in the second step, cutting off the tail tube of the substrate tube after the deposition is finished, and then immersing the substrate tube into the substrate tube containing YbCl₃，AlCl₃，H₃PO₄In solution of (2), wherein YbCl₃The molar concentration is 0.01-0.5%, and AlCl is added₃Molar concentration of 0.01-1.0%, H₃PO₄The molar concentration is 0.1-1%, and the silicon dioxide loose body is doped in a solution soaking mode;

step four: taking out the blow-dried base pipe from the solution in the third step, connecting a tail pipe again, then carrying out oxidation drying and vitrification on the loose silica body in the base pipe, and finally collapsing into a solid rod;

step five: polishing the surface of the solid rod, and fusing and shrinking the sleeve into a whole to obtain an optical fiber preform;

step six: and (3) thinning the optical fiber preform into a quartz optical fiber, coating and curing the low-refractive-index coating inner coating and the acrylic resin optical fiber coating outer coating outside the quartz optical fiber in sequence, and preparing the double-cladding active optical fiber.

Preferably, in the second step, the deposition temperature of the initial pure silicon cladding is 1900-2200 ℃, and the deposition temperature of the initial pure silicon cladding is SiCl₄The deposition flow is 20-300 sccm, the deposition speed is 10-100 mm/min, and the number of deposition layers is 2-5; the deposition temperature of the filling region is 1700-1900 ℃, and SiO is₂Flow rate: 200-300sccm, GeCl₄Flow rate: 50-100sccm, BCl₃Flow rate: 800-; the deposition temperature of the pure silicon cladding is 1900-2200 ℃, and the deposition temperature of SiCl is₄The deposition flow is 20-300 sccm, the deposition speed is 50-100 mm/min, and the number of deposition layers is 2-10.

Preferably, in the third step, the deposition temperature of the silicon dioxide loose body is 1300-1700 ℃, and the deposition temperature of the SiCl is₄The deposition flow rate is 100-400 sccm.

Preferably, in the fourth step, the doped silica loose body is oxidized by oxygen to the doping element, and the loose body is dried by chlorine.

Compared with the prior art, the invention has the advantages that:

1. according to the invention, four filler structures with refractive indexes lower than those of the fiber core and the cladding are symmetrically introduced around the fiber core of the optical fiber, so that the complexity of the anisotropic processing of the cladding in the later period is avoided, the structure is novel, and the high absorption and good laser performance of the optical fiber can be ensured to the maximum extent;

2. the invention aims to introduce the technological characteristics and advantages of the one-step molding of the optical fiber, the one-step molding on the technology avoids the processing difficulty and the accurate control difficulty, and the method has obvious advantages on cost and personnel configuration;

3. the filler system has the advantages of multiple selectivity, simple process and high maturity, and provides multiple possibilities for the processing technology of the optical fiber.

Drawings

FIG. 1 is a schematic cross-sectional view of a double-clad active optical fiber according to an embodiment of the present invention;

FIG. 2 is a graph of refractive index profile of a double-clad active optical fiber according to an embodiment of the present invention;

fig. 3 is a flow chart of a method for manufacturing a double-clad active optical fiber according to an embodiment of the present invention.

Detailed Description

The present invention will be described in further detail below with reference to the attached drawings, which are illustrative and are not to be construed as limiting the invention. The description of the present embodiment is corresponding to the accompanying drawings, and the description related to the orientation is also based on the description of the accompanying drawings, and should not be construed as limiting the scope of the present invention.

As shown in FIGS. 1-3, the double-clad active optical fiber of the present embodiment includes a core 1 (diameter D)₁) Cladding 2 (diameter D)₂) And a filling region 3 (filling region length L)₁Width of L₂Center-to-center spacing of two filled regions D), inner coating 4 (diameter D)₃) And an outer coating 5 (diameter D)₄). Four rectangular filling areas are symmetrically distributed on two sides of the fiber core, and the cladding surrounds the filling areas.

The preparation method of the double-cladding active optical fiber comprises the following steps:

(1) the preliminary treatment of parent tube makes the parent tube preheat and effectively eliminates the impurity and the bubble of parent tube inner wall, wherein preheats the temperature: preheating time at 800 ℃: 5 min;

(2) performing in-tube deposition, wherein the deposition process comprises pure silicon cladding deposition, filling region deposition and pure silicon cladding deposition in sequence, wherein the deposition temperature of the pure silicon cladding 1 is 1900 ℃, and SiCl is adopted₄The deposition flow is 20-300 sccm, the deposition speed is 10mm/min, and the number of deposition layers is 2; the deposition temperature of the filling area 2 is 1700 ℃, and SiO is generated₂Flow rate: 200sccm, GeCl₄Flow rate: 50sccm, BCl₃Flow rate: 800sccm, and the deposition rate is 20 mm/min; wherein the deposition temperature of the pure silicon cladding 3 is 2200 ℃, SiCl₄The deposition flow is 300sccm, the deposition speed is 100mm/min, and the number of deposition layers is 10;

after the deposition 2 in the filling area is finished, directional etching is carried out, the base tube is kept to not rotate any more, corrosive gas is introduced into the base tube, two walls of the base tube are heated by moving two fire sources outside the base tube back and forth along the axial direction of the base tube, two opposite walls of an annular stress ring in the base tube are heated respectively, the corrosive gas corrodes the heating part of the stress ring to be etched gradually, two fire heads are always symmetrical outside the base tube, the times of moving the fire heads back and forth are etching times which are 15, the base tube is turned over for 180 ℃ each time to ensure the etching consistency of the two walls of the stress ring, and two completely separated crescent filling areas are obtained by completely etching the two walls; the base tube is turned 90 degrees and the above operation is repeated until the two walls are completely cut through to obtain two other completely separated crescent-shaped filling area regions.

(3) The deposition of loose silica on the inner surface of the substrate tube was carried out, and the substrate tube was cut off at the end of the deposition and then dipped into a solution containing YbCl3, AlCl3, H3PO 4. Wherein YbCl₃The molar concentration is 0.01-0.5%, and AlCl is added₃Molar concentration of 0.01-1.0%, H₃PO₄The molar concentration is 0.1-1%;

(4) connecting the base pipe dried in the step (3) with a tail pipe again, then carrying out oxidation drying on the loose body of the silicon dioxide in the base pipe, and finally sintering into a solid rod;

(5) polishing and sleeving the optical fiber preform;

(6) step six: and (3) thinning the optical fiber preform into a quartz optical fiber, coating and curing the low-refractive-index coating inner coating and the acrylic resin optical fiber coating outer coating outside the quartz optical fiber in sequence, and preparing the double-cladding active optical fiber.

In addition to the above embodiments, the present invention also includes other embodiments, and any technical solutions formed by equivalent transformation or equivalent replacement should fall within the scope of the claims of the present invention.