CN106932858B - Double-cladding active optical fiber and manufacturing method thereof - Google Patents
Double-cladding active optical fiber and manufacturing method thereof Download PDFInfo
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- CN106932858B CN106932858B CN201710225014.7A CN201710225014A CN106932858B CN 106932858 B CN106932858 B CN 106932858B CN 201710225014 A CN201710225014 A CN 201710225014A CN 106932858 B CN106932858 B CN 106932858B
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
- C03B37/01—Manufacture of glass fibres or filaments
- C03B37/012—Manufacture of preforms for drawing fibres or filaments
- C03B37/01205—Manufacture of preforms for drawing fibres or filaments starting from tubes, rods, fibres or filaments
- C03B37/01211—Manufacture of preforms for drawing fibres or filaments starting from tubes, rods, fibres or filaments by inserting one or more rods or tubes into a tube
- C03B37/01222—Manufacture of preforms for drawing fibres or filaments starting from tubes, rods, fibres or filaments by inserting one or more rods or tubes into a tube for making preforms of multiple core optical fibres
Abstract
The invention discloses a double-cladding active optical fiber and a manufacturing method thereof, wherein the double-cladding active optical fiber sequentially comprises the following components from inside to outside: the fiber comprises a fiber core, an inner cladding, an outer cladding and a protective coating; m filling regions are arranged in the inner cladding, M is a positive integer, and the filling regions are composed of fillers with refractive indexes smaller than that of the inner cladding. The invention solves the technical problem of how to improve the absorption of the cladding pump on the premise of keeping the doping concentration of the fiber core unchanged in the double-cladding active optical fiber in the prior art. In addition, the design can allow the preparation of a circular active optical fiber, greatly improve the matching property and the compatibility with a passive optical fiber, and further improve the efficiency and the reliability of the optical fiber laser.
Description
Technical Field
The invention relates to the technical field of optical fibers, in particular to a double-clad active optical fiber and a manufacturing method thereof.
Background
The technical breakthrough of the high-power fiber laser is started from a double-cladding pumping concept proposed by Snitzer et al in 1988, and is different from the design of common communication fibers, except for an inner cladding surrounding a fiber core, the double-cladding fiber is additionally provided with an outer cladding formed by a low-refractive-index coating, so that the fiber core has a higher refractive index relative to the inner cladding and the inner cladding relative to the outer cladding, a double-waveguide structure of the fiber core and the cladding is formed, the fiber core doped with rare earth ions can be used as a gain medium of laser, and the cladding waveguide can be used for transmitting a pumping light source. The spot size of multimode semiconductor laser emitted by the end face in the long axis direction is generally more than 100 microns, and the diameter of the optical fiber can be flexibly controlled in the range of dozens to hundreds of microns, so that the double-clad optical fiber can effectively utilize high-power low-brightness semiconductor laser as a pumping light source, and a high-power solid laser with an all-fiber structure becomes possible. It is obvious that the pump light propagating in the cladding is absorbed by the rare earth ions only when it passes through the core, and therefore the cladding pump absorption coefficient is generally much lower than the core pump absorption coefficient, and the ratio of the two ultimately depends on the ratio of the cross-sectional areas of the core and the cladding. In addition, a part of the cladding pump light is transmitted in a spiral optical mode and never passes through the fiber core, so that the double-cladding active fiber is generally made into a non-circular cross section, such as an octagon or a 'D' shape, etc., in order to improve the pump absorption efficiency. The octagonal double-cladding active optical fiber is the mainstream optical fiber design for manufacturing a high-power optical fiber laser at present.
The double-clad active optical fiber is an important component of an optical fiber laser, has a lower refractive index outer cladding layer compared with the conventional optical fiber, and mainly comprises a fiber core, an inner cladding layer, a lower refractive index outer cladding layer and a protective coating (a high refractive index coating layer).
The existing double-clad active optical fiber has the following disadvantages:
(1) in the use of fiber lasers, the reduction of the used length of the fiber and the reduction of the nonlinear effect are desired, and therefore, the cladding pumping absorption of the double-cladding active fiber needs to be improved, and the cladding pumping absorption is generally improved by increasing the doping concentration of a fiber core, but the optical darkening phenomenon of the fiber is obvious. Therefore, how to increase the cladding pumping absorption while keeping the doping concentration of the core unchanged has become a problem to be solved.
(2) Under the condition of meeting the same coupling power requirement, the sectional area of the cladding can be properly reduced by improving the numerical aperture of the cladding, so that the pumping absorption of the ytterbium-doped fiber is improved, but the existing low-refractive-index coating is difficult to change greatly due to the property of the material; although the numerical aperture of the cladding can be greatly improved by adopting the air hole cladding, the existence of the air holes makes the optical fiber of the type difficult to cut and weld and difficult to match with the existing optical device.
(3) 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.
Disclosure of Invention
The application provides a double-cladding active optical fiber and a manufacturing method thereof, which solve the technical problem that in the prior art, the double-cladding active optical fiber improves the pump absorption on the premise of keeping the same fiber core doping concentration.
On one hand, the application provides the following technical scheme through an embodiment:
a double-clad active optical fiber comprising, in order from the inside to the outside: the fiber comprises a fiber core, an inner cladding, an outer cladding and a protective coating; m filling regions are arranged in the inner cladding, M is a positive integer, and the filling regions are composed of fillers with refractive indexes smaller than that of the inner cladding.
Preferably, the M filling regions are randomly distributed in the inner cladding, or the M filling regions are distributed in a central symmetry manner.
Preferably, the size and shape of the M filling regions are arbitrary, or the size and shape of the M filling regions are the same.
Preferably, the fill region is doped silica glass.
Preferably, the doping elements in the doped silica glass comprise any combination of F, B, P, Ge, Al.
Preferably, the inner cladding is silica glass.
Preferably, the outer cladding is fluorine-doped silica glass or boron-doped silica glass or a low refractive index resin.
Preferably, the double-clad active optical fiber has a circular outer shape in cross section.
Preferably, the outer shape of the cross section of the double-clad active optical fiber is polygonal.
On the other hand, the present application provides the following technical solutions through an embodiment:
a method of fabricating a double clad active optical fiber, comprising:
preparing an active prefabricated rod, wherein the active prefabricated rod comprises a core layer and an inner cladding layer;
combining the active core rod and the sleeve pipe, and melting to obtain a first optical fiber preform;
drilling M filling areas on the cross section of the first optical fiber prefabricated rod to obtain a second optical fiber prefabricated rod, wherein M is a positive integer;
inserting a filler rod into each filling area to obtain a third optical fiber preform, wherein the refractive index of the filler rod is smaller than that of the inner cladding;
and drawing the third optical fiber perform at high temperature, and sequentially coating an outer cladding layer and a protective coating on the surface of the third optical fiber perform to obtain the double-clad active optical fiber.
One or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages:
in the embodiment of the invention, an optical fiber design for improving the cladding pumping absorption of a double-cladding active optical fiber is disclosed, which sequentially comprises the following components from inside to outside: the fiber comprises a fiber core, an inner cladding, an outer cladding and a protective coating; m filling regions are arranged in the inner cladding, and M is a positive integer. The M filling regions are arranged in the inner cladding, and the refractive index of the filler is lower than that of the inner cladding, so that the effective waveguide area of the cladding is reduced, meanwhile, the formation and transmission of spirorotation are greatly inhibited due to the filling regions, the speed of cladding light passing through a fiber core is improved, and the pumping absorption of the cladding can be increased due to the combination of the filling regions and the fiber core, so that the technical problem of improving the pumping absorption of the double-cladding active optical fiber in the prior art on the premise of keeping the doping concentration of the fiber core unchanged is solved. Furthermore, due to the fact that the suppression of the helical rotation does not need a non-circular optical fiber shape any more, the circular active optical fiber is enabled to be possible, the matching performance and compatibility of the active optical fiber and the passive optical fiber are greatly improved, the geometric control precision in the preparation process of the active optical fiber is improved, welding loss is reduced, and the efficiency and reliability of the laser are improved.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
FIG. 1 is a schematic structural diagram of a double-clad active optical fiber according to an embodiment of the present invention;
FIG. 2 is a flow chart of a method of fabricating a double-clad active optical fiber according to an embodiment of the present invention;
FIG. 3 is a schematic structural diagram of an active core rod in an embodiment of the present invention;
FIG. 4 is a schematic structural diagram of a bushing in an embodiment of the present invention;
FIG. 5 is a schematic view of a structure of a first optical fiber preform according to an embodiment of the present invention;
FIG. 6 is a schematic view of a second optical fiber preform according to an embodiment of the present invention;
FIG. 7 is a schematic structural view of a filler rod in an embodiment of the present invention;
fig. 8 is a schematic structural view of a third optical fiber preform according to an embodiment of the present invention.
Reference numerals: 101-fiber core, 102-active core rod, 103-sleeve, 104-first optical fiber prefabricated rod, 105-second optical fiber prefabricated rod, 106-filling rod, 107-third optical fiber prefabricated rod, 108-inner cladding, 109-outer cladding, 110-protective coating and 111-filling region.
Detailed Description
The embodiment of the application provides an optical fiber design for improving the cladding pumping absorption of a double-cladding active optical fiber and a manufacturing method thereof, and solves the technical problem of improving the pumping absorption of the double-cladding active optical fiber in the prior art on the premise of keeping the same fiber core doping concentration.
In order to solve the technical problems, the general idea of the embodiment of the application is as follows:
a double-clad active optical fiber comprising, in order from the inside to the outside: the fiber comprises a fiber core, an inner cladding, an outer cladding and a protective coating; m filling regions are arranged in the inner cladding, M is a positive integer, and the filling regions are composed of fillers with refractive indexes smaller than that of the inner cladding.
In order to better understand the technical solution, the technical solution will be described in detail with reference to the drawings and the specific embodiments.
Example one
As shown in fig. 1, the present embodiment provides a double-clad active optical fiber, which includes, in order from inside to outside: a core 101, an inner cladding 108, an outer cladding 109 and a protective coating 110; wherein, M filling regions 111 are arranged in the inner cladding layer 108, and M is a positive integer.
Further, the cross section of the double-clad active optical fiber can be polygonal (such as square, regular hexagon, regular octagon, etc.).
Preferably, the cross section of the double-clad active fiber is circular, so that the problems that the common special-shaped double-clad active fiber and the passive fiber are difficult to weld, additional eccentricity is easy to introduce in machining, welding loss is increased, beam quality is reduced, geometric dimension control in a wire drawing process is difficult and the like are solved.
Further, the M filling regions 111 are randomly distributed in the inner cladding 108, or the M filling regions 111 are distributed in a central symmetry manner. The size and shape of the M filling regions 111 are arbitrary, or the size and shape of the M filling regions 111 are the same.
In a specific implementation, the filling region 111 is filled with a filling rod (e.g., filling rod 106) having a refractive index smaller than that of the inner cladding 108, and the filling rod 106 may be a doped silica glass, wherein the doping includes any combination of F (fluorine), B (boron), P (phosphorus), Ge (germanium), and Al (aluminum).
For example, M holes may be drilled in the inner cladding 108, and filler rods 106 inserted into each of the M holes to form a preform and filler rod assembly; and, the M filling rods 106 are centrosymmetric, and M can be 4, 8 or 16(M is an integral multiple of 4). Taking 4 filling rods as an example, the 4 filling rods can be arranged symmetrically up and down and left and right.
In particular implementations, the inner cladding 108 is solid and the inner cladding 108 may be silica glass.
In particular implementations, the outer cladding 109 may be fluorine-doped silica glass or boron-doped silica glass or a low refractive index resin.
In particular implementations, the protective coating 110 is also referred to as a protective layer (or high index coating layer).
The principle of improving the double-clad active fiber cladding pumping absorption in this embodiment is as follows:
when the absorption coefficient of the double-cladding active optical fiber cladding pump is analyzed, an approximate method is adopted, the pump light is absorbed by the fiber core in the propagation process of the inner cladding of the double-cladding active optical fiber, and the cladding pump absorption coefficient of the double-cladding active optical fiber is considered to meet the requirement
Wherein A iscoreIs the area of the core, AcladIs the area of the inner cladding, AinclIs the total area of the filler in the inner cladding, alphacladCladding pumped absorption coefficient, alpha, for double-clad active fiberscoreThe pump absorption coefficient of the core. Therefore, the area A of the core is maintainedcoreAnd the pump absorption coefficient alpha of the corecoreUnder the constant condition, the total area A of the filler in the inner cladding can be increasedinclImproving the cladding pumping absorption coefficient alpha of the double-cladding active optical fiberclad。
Compared with the double-clad active fiber in the prior art, the double-clad active fiber in the embodiment has the advantages that the cladding pumping absorption coefficient is greatly improved, and the position of the inner cladding 108 is replaced by the filling region after the inner cladding is drilled, so that the effective waveguide area of the inner cladding is reduced, and the cladding pumping absorption is improved.
In addition, in the embodiment of the present application, in order to reduce the polarization maintaining performance, the filling rods 106 are arranged in a central symmetry manner, so that the polarization maintaining performance is offset; the filler rod 106 is a fluorine-doped quartz rod, and the polarization maintaining effect is reduced compared to a boron-doped stress rod.
The technical scheme in the embodiment of the application at least has the following technical effects or advantages:
1. in the embodiment of the application, the double-clad active optical fiber is characterized in that the inner cladding region is filled with the filler (namely the filler rod) with the refractive index lower than that of the inner cladding, so that the effective waveguide area of the inner cladding is reduced, and the pumping absorption of the optical fiber is increased, and the pumping absorption of the double-clad active optical fiber cladding is improved on the premise of keeping the doping concentration of the fiber core unchanged.
2. In the embodiment of the application, the double-clad active optical fiber is designed in an all-solid state, and the problems that the double-clad active optical fiber with the air clad is difficult to cut and weld and difficult to match with the existing optical device due to the existence of air holes are solved.
3. In the embodiment of the application, double-clad active optical fiber adopts a circular design, so that the problems that the common special-shaped double-clad active optical fiber and passive optical fiber are difficult to weld, additional eccentricity is easily introduced by machining, the welding loss is increased, the light beam quality is reduced, and the geometric dimension in the wire drawing process is difficult to control are solved.
Example two
Based on the same inventive concept, the present embodiment provides a manufacturing method for improving cladding pump absorption of a double-clad active optical fiber, as shown in fig. 2, including:
step S201: an active core rod 102 is prepared, the active core rod 102 including a core 101 and an inner cladding 108.
In a specific implementation, as shown in fig. 3, the active core rod 102 may be prepared by an MCVD (Modified Chemical Vapor Deposition) process. Specifically, the active core rod 102 is prepared on a quartz substrate tube by sequentially performing the working procedures of etching, inner cladding deposition, core layer deposition, rare earth doping and the like, and then performing rod contraction, polishing and the like.
In a specific implementation, after step S201, the active core rod 102 should be cleaned. Specifically, the active mandrel 102 may be immersed in an HF solution for 200min to remove impurities on the surface of the mandrel.
Step S202: the active core rod 102 is combined with the jacket 103 and fused to obtain a first optical fiber preform 104.
In a specific implementation, as shown in FIG. 4, the sleeve 103 is a quartz sleeve having a circular outer diameter. As shown in fig. 5, an active core rod 102 and a sleeve 103 are combined, the sleeve 103 is sleeved outside the active core rod 102, the matching error between the inner diameter of the sleeve 103 and the diameter of the active core rod 102 is within 0.5mm, and the active core rod 102 and the sleeve 103 are fused in a sleeve system to obtain a solid first optical fiber preform 104.
Step S203: drilling M filling regions 111 on the cross section of the first optical fiber preform 104 to obtain a second optical fiber preform 105; wherein M is a positive integer.
In a specific implementation, the M filling regions 111 are centrosymmetric. For example: as shown in fig. 6, the first optical fiber preform 104 may be placed in a drilling apparatus to drill 4 filled regions 111 symmetrically, and the 4 filled regions 111 are symmetrical up and down, left and right.
Step S204: a filler rod 106 is inserted into each of the filled regions 111 to obtain a third optical fiber preform 107.
In a specific implementation, the filling region 111 is filled with a filling rod 106 having a refractive index smaller than that of the inner cladding as shown in FIG. 7, which may be a fluorine-doped quartz rod.
In a specific implementation process, before step S204, the method further includes: cleaning the second optical fiber preform 105; polishing the filling rod; the polished filler rod 106 is cleaned. When the second optical fiber preform 105 is cleaned, the second optical fiber preform 105 may be placed in an alkaline cleaner for ultrasonic cleaning for more than 15min, then placed in an organic cleaner for ultrasonic cleaning for more than 15min, and then placed in an HF solution for soaking for more than 15min to remove impurities on the surface of the second optical fiber preform 105. When the filler rod 106 is polished, it is required to ensure that the diameter of the polished filler rod 106 is smaller than the diameter of the filling area 111, and the difference between the diameter of the polished filler rod 106 and the diameter of the filling area 111 is controlled within a preset value, where the preset value ranges from 0.3mm to 0.5mm, for example: 0.3mm, 0.4mm, 0.5 mm. When the polished filler rod 106 is cleaned, the filler rod 106 may be placed in an alkaline cleaning agent for ultrasonic cleaning for more than 15min, then placed in an organic cleaning agent for ultrasonic cleaning for more than 15min, and then placed in an HF solution for soaking for more than 15min to remove impurities on the surface of the filler rod 106.
In a specific implementation, a filler rod 106 is inserted into each of the filled regions 111 of the second optical fiber preform 105 to obtain a third optical fiber preform 107, as shown in FIG. 8.
Step S205: the third optical fiber preform 107 is drawn at a high temperature, and the outer cladding 109 and the protective coating 110 are sequentially coated on the surface to obtain a double-clad active optical fiber.
In the specific implementation process, the third optical fiber preform 107 is placed on an optical fiber drawing tower, the third optical fiber preform 107 is drawn and coated in a molten state, and an outer cladding 109 and a protective coating 110 are formed on the surface of the third optical fiber preform, so that the double-clad active optical fiber shown in fig. 1 is finally obtained, wherein the cross section of the double-clad active optical fiber is circular.
The technical scheme in the embodiment of the application at least has the following technical effects or advantages:
1. in the embodiment of the application, the double-clad active optical fiber is characterized in that the inner cladding region is filled with the filler (namely the filler rod) with the refractive index lower than that of the inner cladding, so that the effective waveguide area of the inner cladding is reduced, and the pumping absorption of the optical fiber is increased, and the pumping absorption of the double-clad active optical fiber cladding is improved on the premise of keeping the doping concentration of the fiber core unchanged.
2. In the embodiment of the application, the double-clad active optical fiber is designed in an all-solid state, and the problems that the double-clad active optical fiber with the air clad is difficult to cut and weld and difficult to match with the existing optical device due to the existence of air holes are solved.
3. In the embodiment of the application, double-clad active optical fiber adopts a circular design, so that the problems that the common special-shaped double-clad active optical fiber and passive optical fiber are difficult to weld, additional eccentricity is easily introduced by machining, the welding loss is increased, the light beam quality is reduced, and the geometric dimension in the wire drawing process is difficult to control are solved.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (1)
1. A double-clad active optical fiber, comprising, in order from the inside to the outside: the fiber comprises a fiber core, an inner cladding, an outer cladding and a protective coating; the double-clad active optical fiber comprises an inner cladding, an outer cladding, M filling regions, a filler and a doped element, wherein the inner cladding is made of silica glass, the outer cladding is made of low-refractive-index resin, the inner cladding is internally provided with M filling regions, M is a positive integer and is an integral multiple of 4, the M filling regions are distributed in a centrosymmetric manner, the size and the shape of the M filling regions are the same, each filling region is composed of the filler with the refractive index smaller than that of the inner cladding, the filler is doped silica glass, the doped element comprises F (fluorine), B (boron), P (phosphorus), Ge (germanium) and Al (aluminum), and the cross section of the double-clad active optical fiber is circular in shape.
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| CN112596151B (en) * | 2020-11-24 | 2022-11-04 | 江苏法尔胜光电科技有限公司 | Erbium-doped polarization-maintaining active optical fiber and preparation method thereof |
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| CN102955199A (en) * | 2012-11-09 | 2013-03-06 | 上海飞博激光科技有限公司 | Double-cladding optical fiber for optical fiber laser or optical fiber amplifier |
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