CN111484242B - Bragg optical fiber preform, Bragg optical fiber, preparation method and application thereof - Google Patents

Bragg optical fiber preform, Bragg optical fiber, preparation method and application thereof Download PDF

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CN111484242B
CN111484242B CN202010443493.1A CN202010443493A CN111484242B CN 111484242 B CN111484242 B CN 111484242B CN 202010443493 A CN202010443493 A CN 202010443493A CN 111484242 B CN111484242 B CN 111484242B
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refractive index
medium
optical fiber
low
refractive
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CN111484242A (en
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孟悦
杨坤
杨晨
张心贲
曹蓓蓓
何亮
喻建刚
童维军
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Sichuan Lefei Photoelectric Technology Co.,Ltd.
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Yangtze Optical Fibre and Cable Co Ltd
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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
    • C03B37/02—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor
    • C03B37/025—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor from reheated softened tubes, rods, fibres or filaments, e.g. drawing fibres from preforms
    • C03B37/027—Fibres composed of different sorts of glass, e.g. glass optical fibres
    • 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

Abstract

The invention discloses a Bragg optical fiber preform, a Bragg optical fiber, a preparation method and application thereof, belonging to the field of optics and laser photoelectrons, wherein the optical fiber comprises a high-refractive-index fiber core with a relative refractive index difference delta of 0.05-0.55%, and an optical fiber cladding consisting of high-refractive-index media and low-refractive-index media which are arranged in a staggered manner according to a certain period, wherein the relative refractive index difference delta 1 of the high-refractive-index media is 0.05-1.1%, and the thickness of each layer is 1-3 mu m; the relative refractive index difference delta 2 of the low-refractive-index medium is-0.18% -0.005%, and the thickness of each layer is 3-9 mu m; a layer of high-refractive-index medium and an adjacent layer of low-refractive-index medium form a cycle, a region outside the high-refractive-index and low-refractive-index media which are periodically arranged is made of pure silica materials, a low-refractive-index polymer is coated in the optical fiber, and a high-refractive-index polymer is coated on the outer layer of the optical fiber. The optical fiber can obtain a large mode field area at the wavelength of 1030-1110 nm, supports transmission of a fundamental mode and effectively filters a high-order mode.

Description

Bragg optical fiber preform, Bragg optical fiber, preparation method and application thereof
Technical Field
The invention belongs to the field of optics and laser photoelectrons, and particularly relates to a Bragg optical fiber preform, a Bragg optical fiber, and a preparation method and application thereof.
Background
In order to maintain single-mode operation to ensure beam quality, the conventional means generally includes reducing the numerical aperture of a fiber core or combining an external mode selection technology with a multimode fiber, but the former has the problem of too large bending loss, and the former is contradictory to the latter in terms of low numerical aperture and pursuit of high doping concentration, and the latter is not favorable for realizing compact packaging and miniaturization of a system, so how to obtain a large mode field area, and high gain and excellent beam quality are always research hotspots and difficulties in the field of high-power fiber lasers.
Disclosure of Invention
Aiming at the defects or improvement requirements of the prior art, the invention provides a Bragg fiber preform, a Bragg fiber, a preparation method and application thereof, aiming at reasonably designing the refractive indexes of a fiber core and a cladding, the thickness of each layer and the number of layers of high-low refractive index media of the cladding, so that compared with the common double-cladding rare earth-doped fiber, the fiber core can tolerate higher doping and higher numerical aperture to ensure that a fundamental mode is still bound in the fiber core for stable transmission, and unnecessary high-order modes are leaked due to high loss, and finally the output close to the diffraction limit is obtained, namely, the fiber core of the fiber has the effect of mode selection, wherein the fiber core of the fiber can be an active fiber doped with rare earth or a passive fiber doped with germanium, the former is used as a gain medium of a laser, and the latter is used as a transmission medium of the laser.
To achieve the above object, according to one aspect of the present invention, there is provided a bragg optical fiber preform including a core made of a high refractive index material and a cladding made of a high refractive index medium and a low refractive index medium alternately arranged at a certain period;
the diameter of the fiber core is 2-6 mm, the relative refractive index difference delta of a high-refractive-index material forming the fiber core is 0.05% -0.55%, the relative refractive index difference delta 1 of a high-refractive-index medium is 0.05% -1.1%, and the thickness D of each layer of the high-refractive-index medium10.1-0.3 mm, the relative refractive index difference delta 2 of the low-refractive-index medium is-0.18% -0.005%, and the thickness D of each layer of the low-refractive-index medium20.3-1 mm, a layer of high refractive index medium plusAnd the adjacent layer of low-refractive-index medium forms a period, and the region outside the high-refractive-index and low-refractive-index medium which is periodically arranged is made of pure silicon dioxide material.
Preferably, is prepared from
Figure BDA0002504782490000021
Determining a relative refractive index difference Δ of the core, where ncoreIs the refractive index of the core, nSiIs a pure silicon refractive index;
by
Figure BDA0002504782490000022
Determining a relative refractive index difference Δ 1 of the high refractive index medium in the cladding, wherein nGeIs the refractive index of the high refractive index medium in the cladding;
by
Figure BDA0002504782490000023
Determining the relative refractive index difference delta 2 of the low-refractive-index medium in the cladding, wherein nFIs the refractive index of the low refractive index medium in the cladding.
Preferably, the relative refractive index difference Δ of the high refractive index material constituting the core is 0.085% to 0.19%, the relative refractive index difference Δ 1 of the high refractive index medium is 0.2% to 0.34%, and the relative refractive index difference Δ 2 of the low refractive index medium is-0.06% to-0.02%.
Preferably, the high refractive index material of the core is germanium-doped silica glass or rare earth ion-doped silica glass.
Preferably, the cladding region of the preform has 10 to 16 of the periods, and the outer diameter of the preform is 20 to 60 mm.
According to another aspect of the present invention, there is provided a method of fabricating a bragg optical fiber preform, including:
(1) and depositing a cladding and a core in a liner tube made of pure silica material, and then fusing the deposited hollow tube into a solid rod, wherein the relative refractive index difference delta of the core of the solid rod is 0.05-0.55 percent of the total weight of the alloy, and the diameter of the alloy is 2-6 mm; the cladding is formed by high refractive index medium and low refractive index medium which are arranged in a staggered mode according to a certain period, the relative refractive index difference delta 1 of the high refractive index medium is 0.05% -1.1%, and the thickness D of each layer of the high refractive index medium10.1-0.3 mm, the relative refractive index difference delta 2 of the low-refractive-index medium is-0.18% -0.005%, and the thickness D of each layer of the low-refractive-index medium2The thickness of the prefabricated rod is 0.3-1 mm, a layer of high-refractive-index medium and an adjacent layer of low-refractive-index medium form a period, a plurality of periods are arranged in a cladding region of the prefabricated rod, regions except the periodically-arranged high-refractive-index and low-refractive-index medium are made of pure silicon dioxide materials, and the outer diameter of the prefabricated rod is 25-70 mm;
(2) and (2) polishing or corroding the solid rod obtained in the step (1) until the outer diameter is 20-60 mm.
Preferably, the relative refractive index difference Δ of the core of the solid rod is 0.085% -0.19%, the relative refractive index difference Δ 1 of the high refractive index medium is 0.2% -0.34%, the relative refractive index difference Δ 2 of the low refractive index medium is-0.06% -0.02%, and the cladding region of the preform has 10-16 periods.
According to another aspect of the present invention, there is provided a bragg fiber, including a core with a high refractive index, the core having a diameter of 20 to 50 μm, the core having a relative refractive index difference Δ of 0.05% to 0.55%, and a cladding of the fiber including high refractive index media and low refractive index media alternately arranged in a certain period, wherein the relative refractive index difference Δ 1 of the high refractive index media is 0.05% to 1.1%, and a thickness d of each layer of the high refractive index media11-3 um, the relative refractive index difference delta 2 of the low-refractive-index medium is-0.18% -0.005%, and the thickness d of each layer of the low-refractive-index medium2Is 3 ~ 9um, one deck high refractive index medium and adjacent one deck low refractive index medium constitute a cycle, and the region outside the high low refractive index medium that periodically arranges is pure silica material, the cladding diameter of optic fibre is 250 ~ 600um, the undercoating of optic fibre is low refractive index polymer, the relative refractive index difference of low refractive index polymerDelta 3 is less than or equal to-5 percent, the outer diameter of the optical fiber is 350-700 mu m, the outer coating of the optical fiber is a high-refractive-index polymer, the relative refractive index difference delta 4 of the high-refractive-index polymer is more than or equal to 3.5 percent, and the outer diameter of the optical fiber is 500-800 mu m.
Preferably, is prepared from
Figure BDA0002504782490000041
Determining the relative refractive index difference Δ 3 of the inner coating of said fiber from
Figure BDA0002504782490000042
Determining the relative refractive index difference Δ 4 of the outer coating of the optical fiber, wherein n3Is the refractive index of the inner coating of the optical fiber, nSiIs a refractive index of pure silicon, n4Is the refractive index of the outer coating of the optical fiber.
Preferably, the relative refractive index difference delta of the fiber core is 0.085% -0.19%, the relative refractive index difference delta 1 of the high refractive index medium is 0.2% -0.34%, the relative refractive index difference delta 2 of the low refractive index medium is-0.06% -0.02%, and the cladding of the optical fiber has 10-16 periods.
According to another aspect of the present invention, there is provided a method of manufacturing a bragg fiber, including:
the optical fiber perform prepared by the preparation method of the Bragg optical fiber perform is drawn into a rare earth doped Bragg optical fiber with the cladding of 250-600 um, and is coated with a low refractive index coating with the relative refractive index difference delta 3 being less than or equal to-5% to form an inner coating of the optical fiber, the outer diameter of the inner coating is 350-700 um, a high refractive index coating with the relative refractive index difference delta 4 being greater than or equal to 3.5% is coated to form an outer coating of the optical fiber, and the outer diameter of the outer coating is 500-800 um.
According to another aspect of the present invention there is provided a use of a bragg fibre comprising: the single-mode laser can be used as a gain medium or a transmission medium of the optical fiber laser to realize mode selection and obtain single-mode laser in the wavelength range of 1030 nm-1110 nm.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
according to the invention, the Bragg structure with high and low refractive index media in staggered periodic arrangement is introduced into the cladding of the optical fiber, the refractive index of the fiber core, the refractive index of the cladding periodic arrangement media and the thickness of each layer are reasonably designed to obtain a stable transmission fundamental mode, and meanwhile, a high-order mode is leaked due to large loss, so that the effect of mode selection is finally realized.
Drawings
FIG. 1 is a schematic view of a Bragg optical fiber preform according to example 1 of the present invention;
FIG. 2 is a schematic cross-sectional view of a Bragg fiber according to embodiment 1 of the present invention;
FIG. 3 is a radial refractive index profile of a Bragg fiber according to example 1 of the present invention;
FIG. 4 is a graph of normalized intensity along the axial direction for each order mode of a Bragg fiber according to example 1 of the present invention;
FIG. 5 is a schematic view of a Bragg optical fiber preform according to example 2 of the present invention;
FIG. 6 is a schematic cross-sectional view of a Bragg fiber according to embodiment 2 of the present invention;
FIG. 7 is a radial refractive index profile of a Bragg fiber according to embodiment 2 of the present invention;
FIG. 8 is a graph of normalized intensity along the axial direction for each order mode of a Bragg fiber according to example 2 of the present invention;
the same reference numbers will be used throughout the drawings to refer to the same or like elements or structures, wherein: 1 is a fiber core of a Bragg optical fiber preform, 2 is a medium with a high refractive index in a cladding, 3 is a medium with a low refractive index in the cladding, and 4 is a pure silicon dioxide medium in the cladding; 21 is the core of the Bragg fiber, 22 is medium with high refractive index in the cladding, 23 is medium with low refractive index in the cladding, 24 is pure silica medium in the cladding, 25 is the inner coating of the fiber, and 26 is the outer coating of the fiber.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
In a first aspect, an embodiment of the present invention provides a bragg optical fiber preform, including a fiber core made of a high refractive index material, the fiber core having a diameter of 2-6 mm and a relative refractive index difference Δ of 0.05% -0.55%, wherein the high refractive index material of the fiber core may be germanium-doped silica glass or rare earth ion-doped silica glass; the optical fiber perform rod also comprises a cladding which is formed by high refractive index medium and low refractive index medium which are arranged in a certain period in a staggered mode, wherein the layer close to the fiber core is the high refractive index medium, the relative refractive index difference delta 1 of the high refractive index medium is 0.05% -1.1%, and the thickness D of each layer of the high refractive index medium10.1-0.3 mm, the relative refractive index difference delta 2 of the low-refractive-index medium is-0.18% -0.005%, and the thickness D of each layer of the low-refractive-index medium2The thickness of the prefabricated rod is 0.3-1 mm, a layer of high-refractive-index medium and an adjacent layer of low-refractive-index medium form a period, 10-16 periods are formed in a cladding region of the prefabricated rod, regions except the high-refractive-index medium and the low-refractive-index medium which are periodically arranged are made of pure silicon dioxide materials, and the outer diameter of a cladding of the prefabricated rod is 20-60 mm.
Wherein, the relative refractive index difference Delta of the fiber core is calculated according to the following method:
Figure BDA0002504782490000061
wherein n iscoreIs the core refractive index, nSiIs a pure silicon refractive index.
Wherein, the relative refractive index difference Delta 1 of the high refractive index medium in the cladding is calculated according to the following method:
Figure BDA0002504782490000062
wherein n isGeIs the refractive index of the high refractive index medium in the cladding, nSiIs pure siliconRefractive index.
Wherein, the relative refractive index difference delta 2 of the low-refractive-index medium in the cladding is calculated according to the following method:
Figure BDA0002504782490000063
wherein n isFIs the refractive index of the low-refractive-index medium in the cladding, nSiIs a pure silicon refractive index.
Furthermore, the relative refractive index difference delta of the high refractive index material forming the fiber core is 0.085-0.19%, the relative refractive index difference delta 1 of the high refractive index medium is 0.2-0.34%, and the relative refractive index difference delta 2 of the low refractive index medium is-0.06% -0.02%.
In a second aspect, an embodiment of the present invention provides a method for preparing a bragg optical fiber preform, including the following steps:
(1) depositing a cladding and a fiber core in a liner tube made of pure silica materials, and then fusing the deposited hollow tube into a solid rod, wherein the relative refractive index difference delta of the fiber core of the solid rod is 0.05-0.55%, and the diameter of the fiber core of the solid rod is 2-6 mm; the cladding is composed of high refractive index medium and low refractive index medium arranged alternately according to a certain period, wherein the relative refractive index difference delta 1 of the high refractive index medium is 0.05% -1.1%, and the thickness D of each layer of the high refractive index medium10.1-0.3 mm, the relative refractive index difference delta 2 of the low-refractive-index medium is-0.18% -0.005%, and the thickness D of each layer of the low-refractive-index medium2The thickness of the prefabricated rod is 0.3-1 mm, a layer of high-refractive-index medium and an adjacent layer of low-refractive-index medium form a period, the cladding region of the prefabricated rod has 10-16 periods, regions except the high-refractive-index and low-refractive-index medium which are periodically distributed are made of pure silicon dioxide materials, and the outer diameter of the prefabricated rod is 25-70 mm;
(2) and (2) polishing or corroding the solid rod obtained in the step (1) until the outer diameter is 20-60 mm.
MCVD or PCVD can be used for depositing a cladding and a fiber core in a liner tube made of pure silica materials, and the deposited hollow tube can be fused into a solid rod on a horizontal fusion lathe.
Furthermore, the relative refractive index difference delta of the fiber core of the solid rod is 0.085-0.19%, the relative refractive index difference delta 1 of the medium with high refractive index is 0.2-0.34%, and the relative refractive index difference delta 2 of the medium with low refractive index is-0.06% -0.02%.
On the other hand, the embodiment of the invention provides a Bragg fiber, which comprises a fiber core with a high refractive index, wherein the diameter of the fiber core is 20-50 um, the relative refractive index difference delta is 0.05% -0.55%, and the high refractive index material of the fiber core can be germanium-doped silica glass or rare earth ion-doped silica glass; the cladding of the optical fiber consists of high-refractive-index media and low-refractive-index media which are arranged in a staggered mode according to a certain period, wherein the relative refractive index difference delta 1 of the high-refractive-index media is 0.05% -1.1%, and the thickness d of each layer of the high-refractive-index media11-3 um, the relative refractive index difference delta 2 of the low-refractive-index medium is-0.18% -0.005%, and the thickness d of each layer of the low-refractive-index medium23-9 um, a period is formed by adding one layer of high refractive index medium and an adjacent layer of low refractive index medium, the optical fiber has 10-16 such periods, the region outside the periodically arranged high and low refractive index medium is made of pure silica materials, the diameter of the cladding of the optical fiber is 250-600 um, the inner coating of the optical fiber is low refractive index polymer, the relative refractive index difference delta 3 is less than or equal to minus 5 percent, the outer diameter is 350-700 um, the outer coating of the optical fiber is high refractive index polymer, the relative refractive index difference delta 4 is more than or equal to 3.5 percent, and the outer diameter is 500-800 um.
The relative refractive index difference delta 3 of the inner coating of the optical fiber is calculated according to the following method:
Figure BDA0002504782490000071
wherein n is3Is the refractive index of the inner coating of the optical fiber, nSiIs a pure silicon refractive index.
Wherein, the relative refractive index difference delta 4 of the external coating of the optical fiber is calculated according to the following method:
Figure BDA0002504782490000081
wherein n is4Is the refractive index of the undercoat, nSiIs a pure silicon refractive index.
Furthermore, the relative refractive index difference delta of the fiber core is 0.085-0.19%, the relative refractive index difference delta 1 of the medium with high refractive index is 0.2-0.34%, and the relative refractive index difference delta 2 of the medium with low refractive index is-0.06% -0.02%.
The optical fiber can obtain a large mode field area at the wavelength of 1030-1110 nm, supports fundamental mode transmission, effectively filters high-order modes, and can be used as a transverse mode selector in a high-power optical fiber laser.
In another aspect, an embodiment of the present invention provides a method for manufacturing a bragg fiber, including:
and drawing the prepared optical fiber preform into a rare earth doped Bragg optical fiber with a cladding of 250-600 um, coating a low-refractive-index coating with a relative refractive index difference delta 3 of less than or equal to minus 5% to form an inner coating of the optical fiber, wherein the outer diameter of the inner coating is 350-700 um, coating a high-refractive-index coating with a relative refractive index difference delta 4 of more than or equal to 3.5% to form an outer coating of the optical fiber, and the outer diameter of the outer coating is 500-800 um.
On the other hand, the embodiment of the invention provides application of the Bragg fiber, which can be used as a gain medium or a transmission medium of a fiber laser to realize mode selection and obtain single-mode laser in a wavelength range of 1030 nm-1110 nm.
Compared with the common double-cladding rare earth-doped fiber, the fiber core can tolerate higher doping and higher numerical aperture and ensure that the fundamental mode is still bound in the fiber core for stable transmission, and the unwanted high-order modes are leaked due to large loss, so that the output close to the diffraction limit is finally obtained, namely, the fiber core of the fiber has the effect of mode selection, the fiber core can be an active fiber doped with rare earth or a passive fiber doped with germanium, the former is used as a gain medium of a laser, and the latter is used as a transmission medium of the laser.
The following examples are intended to illustrate the invention in more detail. The embodiments of the present invention are not limited to the following specific examples. The present invention can be modified and implemented as appropriate within the scope of the main claim.
Example 1
A Bragg optical fiber preform, as shown in FIG. 1, includes a core 1 made of a high refractive index material, which may be ytterbium, aluminum, and phosphorus co-doped silica glass, having a diameter of 2.5mm and a relative refractive index difference Delta of 0.1%; the cladding is arranged by high and low refractive index media in a certain period, wherein the relative refractive index difference delta 1 of the high refractive index medium 2 is 0.3%, and the thickness D of each layer10.2mm, and is made of germanium-doped silica glass; a low refractive index medium 3 having a relative refractive index difference Delta 2 of-0.02% and a thickness D of each layer20.4mm, and the material is fluorine-doped silicon dioxide glass; one layer of high refractive index medium and an adjacent layer of low refractive index medium form a period, the cladding region of the prefabricated rod has 12 periods, the region outside the high refractive index medium and the low refractive index medium which are periodically arranged is made of pure silica material 4, and the outer diameter of the prefabricated rod is 40 mm.
(1) The method comprises the following steps of depositing a cladding and a fiber core on a PCVD lathe by using a liner tube made of pure silica material, wherein the cladding is formed by alternately arranging high-refractive-index media and low-refractive-index media according to a certain period, the relative refractive index difference delta 1 of the high-refractive-index media is 0.3%, and the thickness D of each layer is10.2mm, and is made of germanium-doped silica glass; the relative refractive index difference Delta 2 of the low refractive index medium is-0.02%, and the thickness D of each layer20.4mm, and the material is fluorine-doped silicon dioxide glass; one layer of high refractive index medium plus an adjacent layer of low refractive index medium constitutes one period, and the cladding region of the preform has 12 such periods;
(2) continuously depositing the hollow tube with the cladding obtained in the step (1) on an MCVD lathe to deposit a core layer, and then fusing the hollow tube with the cladding on a horizontal fusing lathe to form a solid rod, wherein the relative refractive index difference delta of the core of the solid rod is 0.1%, the diameter of the core of the solid rod is 2.5mm, the diameter of the rod is 17mm, and the core is made of ytterbium, aluminum and phosphorus co-doped silica glass;
(3) sleeving the solid rod obtained in the step (2) into a sleeve made of pure silicon dioxide material with the inner diameter of 17.5-18 mm, and fusing the solid rod and the sleeve to form a solid rod with the outer diameter of 44-50 mm;
(3) and (3) polishing or corroding the solid rod obtained in the step (2) until the outer diameter is 40 mm.
The preform shown in fig. 1 was drawn into a rare earth doped bragg fiber having a cladding of 400um in a drawing furnace, and coated with a low refractive index coating having a relative refractive index difference Δ 3 of-5% to form an inner coating layer of the optical fiber, and coated with a high refractive index coating having a relative refractive index difference Δ 4 of 3.5% to form an outer coating layer of the optical fiber.
The rare earth doped Bragg fiber prepared by the method has a cross section shown in FIG. 2, comprises a fiber core 21 with a relative refractive index difference delta of 0.1% and a diameter of 25um, and comprises a medium 22 with a high refractive index in a cladding and a relative refractive index difference delta 1 of 0.3%, wherein the thickness d of each layer12um, medium 23 with low refractive index in the cladding, relative refractive index difference delta 2 of-0.02%, and thickness d of each layer24um, one layer of high refractive index medium plus an adjacent layer of low refractive index medium forming a period, the fiber cladding region having 12 such periods, pure silica medium 24 in the cladding of the fiber, the cladding diameter of the fiber being 400 um; the inner coating of the optical fiber is low refractive index polymer 25, the relative refractive index difference delta 3 is-5%, the outer diameter is 500um, the outer coating is high refractive index coating 26, the relative refractive index difference delta 4 is 3.5%, and the outer diameter is 600 um.
The optical fiber finally obtains single-mode output in the wavelength range of 1030 nm-1100 nm, and high-order modes are leaked out quickly due to large attenuation.
Referring to fig. 3, which shows a radial refractive index profile of a bragg optical fiber according to embodiment 1 of the present invention, it can be seen from fig. 3 that the optical fiber is composed of a core and a cladding, wherein the cladding is composed of a high refractive index medium and a low refractive index medium alternately arranged in a certain period, and the cladding medium adjacent to the core is the high refractive index medium.
As shown in fig. 4, which is a graph of normalized intensity of each mode of the bragg fiber in embodiment 1 of the present invention along the axial direction, it can be seen from fig. 4 that the loss of the high-order mode is much larger than that of the fundamental mode, and as the optical beam is transmitted, the high-order mode is gradually cut off, the fundamental mode is retained, that is, the fundamental mode finally occupies an absolute advantage, and the output optical beam has good quality.
Example 2
A Bragg fiber preform, as shown in FIG. 5, includes a core 1 made of a high refractive index material, the diameter of which is 30um, the relative refractive index difference Delta is 0.1%, the core material is silica glass doped with germanium; the cladding is arranged by high and low refractive index media in a staggered manner according to a certain period, wherein the relative refractive index difference delta 1 of the high refractive index medium 2 is 0.3%, and the thickness D of each layer10.2mm, and is made of germanium-doped silica glass; the relative refractive index difference Delta 2 of the low refractive index medium 3 is-0.02%, and the thickness D of each layer20.4mm, and the material is fluorine-doped silicon dioxide glass; one layer of high refractive index medium and an adjacent layer of low refractive index medium form a period, the cladding region of the preform has 12 periods, the region outside the periodically arranged high and low refractive index medium is pure silica material 4, and the outer diameter of the preform is 60 mm.
(1) The method comprises the following steps of simultaneously depositing a cladding and a fiber core on a PCVD lathe by using a liner tube made of pure silica material, fusing the deposited hollow tube into a solid rod on a horizontal fusing lathe, wherein the relative refractive index difference delta of the fiber core of the solid rod is 0.1%, the diameter of the fiber core of the solid rod is 3mm, and the fiber core material is silica glass doped with germanium; the cladding is arranged by high and low refractive index media alternately according to a certain period, wherein the relative refractive index difference delta 1 of the high refractive index media is 0.3%, and the thickness D of each layer10.2mm, and is made of germanium-doped silica glass; the relative refractive index difference Delta 2 of the low refractive index medium is-0.02%, and the thickness D of each layer20.4mm, and the material is fluorine-doped silicon dioxide glass; one layer of high refractive index medium and an adjacent layer of low refractive index medium form a period, a cladding region of the prefabricated rod has 12 periods, regions outside the periodically arranged high and low refractive index medium are made of pure silicon dioxide materials, and the outer diameter of the cladding of the prefabricated rod is 20 mm;
(2) sleeving the solid rod obtained in the step (1) into a sleeve with an inner hole of 22-24 mm, and fusing the solid rod and the sleeve into a solid rod with the rod diameter of 70-80 mm;
(3) and (3) polishing the solid rod obtained in the step (2) until the outer diameter is 60 mm.
The preform shown in fig. 5 was drawn into a rare earth doped bragg fiber with a cladding of 600um in a drawing furnace, and coated with a low refractive index coating having a relative refractive index difference Δ 3 of-5% to form an inner coating of the optical fiber with an outer diameter of 700um, and coated with a high refractive index coating having a relative refractive index difference Δ 4 of 3.5% to form an outer coating of the optical fiber with an outer diameter of 800 um.
The rare earth doped Bragg fiber prepared by the method has a cross section shown in FIG. 6, comprises a fiber core 21 with a relative refractive index difference delta of 0.1% and a diameter of 30um, and comprises a medium 22 with a high refractive index in a cladding, with a relative refractive index difference delta 1 of 0.03, and a thickness d of each layer12um, medium 23 with low refractive index in the cladding, relative refractive index difference delta 2 of-0.02%, and thickness d of each layer24um, one layer of high index medium plus an adjacent layer of low index medium forming a period, the fiber cladding region having 12 such periods, pure silica medium 24 in the cladding of the fiber, the cladding diameter of the fiber being 600 um; the inner coating of the optical fiber is a low refractive index polymer 25, the relative refractive index difference delta 3 is-5%, the outer diameter is 700um, the outer coating is a high refractive index coating 26, the relative refractive index difference delta 4 is 3.5%, and the outer diameter is 800 um.
The optical fiber finally obtains single-mode output in the wavelength range of 1030 nm-1100 nm, and high-order modes are leaked out quickly due to large attenuation.
Referring to fig. 7, which shows a radial refractive index profile of a bragg optical fiber according to embodiment 2 of the present invention, it can be seen from fig. 7 that the optical fiber is composed of a core and a cladding, wherein the cladding is composed of a high refractive index medium and a low refractive index medium alternately arranged in a certain period, and the cladding medium adjacent to the core is the high refractive index medium.
As shown in fig. 8, which is a graph of normalized intensity of each mode of the bragg fiber in embodiment 2 of the present invention along the axial direction, it can be seen from fig. 8 that the loss of the high-order mode is much larger than that of the fundamental mode, and as the optical beam is transmitted, the high-order mode is gradually cut off, the fundamental mode is retained, that is, the fundamental mode finally occupies an absolute advantage, and the output optical beam has good quality.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (8)

1. A Bragg optical fiber prefabricated rod is characterized by comprising a fiber core made of high-refractive-index materials and a cladding which is formed by high-refractive-index media and low-refractive-index media which are arranged in a staggered mode according to a certain period;
the diameter of the fiber core is 2-6 mm, the relative refractive index difference delta of a high-refractive-index material forming the fiber core is 0.05% -0.55%, the relative refractive index difference delta 1 of a high-refractive-index medium is 0.05% -1.1%, and the thickness D of each layer of the high-refractive-index medium10.1-0.3 mm, the relative refractive index difference delta 2 of the low-refractive-index medium is-0.18% -0.005%, and the thickness D of each layer of the low-refractive-index medium2The thickness of the high-refractive-index medium is 0.3-1 mm, a layer of high-refractive-index medium and an adjacent layer of low-refractive-index medium form a period, and the region outside the periodically arranged high-refractive-index and low-refractive-index media is made of pure silicon dioxide materials;
wherein, by
Figure FDA0003051647560000011
Determining a relative refractive index difference Δ of the core, where ncoreIs the refractive index of the core, nSiIs a pure silicon refractive index;
by
Figure FDA0003051647560000012
Determining a relative refractive index difference Δ 1 of the high refractive index medium in the cladding, wherein nGeIs the refractive index of the high refractive index medium in the cladding;
by
Figure FDA0003051647560000013
Determining the relative refractive index difference delta 2 of the low-refractive-index medium in the cladding, wherein nFIs the refractive index of the low refractive index medium in the cladding.
2. A bragg optical fiber preform according to claim 1, wherein the relative refractive index difference Δ of the high refractive index material constituting the core is 0.085% to 0.19%, the relative refractive index difference Δ 1 of the high refractive index medium is 0.2% to 0.34%, and the relative refractive index difference Δ 2 of the low refractive index medium is-0.06% to-0.02%.
3. A Bragg fiber preform according to claim 2, wherein the cladding region of the preform has 10 to 16 of said periods and the outer diameter of the preform is 20 to 60 mm.
4. A method for preparing a Bragg optical fiber preform, comprising:
(1) depositing a cladding and a fiber core in a liner tube made of pure silica materials, and then fusing the deposited hollow tube into a solid rod, wherein the relative refractive index difference delta of the fiber core of the solid rod is 0.05-0.55%, and the diameter of the solid rod is 2-6 mm; the cladding is formed by high refractive index medium and low refractive index medium which are arranged in a staggered mode according to a certain period, the relative refractive index difference delta 1 of the high refractive index medium is 0.05% -1.1%, and the thickness D of each layer of the high refractive index medium10.1-0.3 mm, the relative refractive index difference delta 2 of the low-refractive-index medium is-0.18% -0.005%, and the thickness D of each layer of the low-refractive-index medium2The thickness of the prefabricated rod is 0.3-1 mm, a layer of high-refractive-index medium and an adjacent layer of low-refractive-index medium form a period, a plurality of periods are arranged in a cladding region of the prefabricated rod, regions except the periodically-arranged high-refractive-index and low-refractive-index medium are made of pure silicon dioxide materials, and the outer diameter of the prefabricated rod is 25-70 mm;
(2) polishing or corroding the solid rod obtained in the step (1) until the outer diameter is 20-60 mm;
wherein, by
Figure FDA0003051647560000021
Determining the relative refractive index difference delta of the core, where ncoreIs the refractive index of the core, nsiIs a pure silicon refractive index;
by
Figure FDA0003051647560000022
Determining the relative refractive index difference Delta 1 of the high refractive index medium in the cladding, wherein nGeIs the refractive index of the high refractive index medium in the cladding;
by
Figure FDA0003051647560000023
Determining the relative refractive index difference Delta 2 of the low-refractive-index medium in the cladding, wherein nFThe refractive index of the low refractive index medium in the cladding.
5. The Bragg fiber is characterized by comprising a fiber core with a high refractive index, wherein the diameter of the fiber core is 20-50 um, the relative refractive index difference delta of the fiber core is 0.05% -0.55%, a cladding of the fiber consists of a high refractive index medium and a low refractive index medium which are arranged in a certain period in a staggered mode, wherein the relative refractive index difference delta 1 of the high refractive index medium is 0.05% -1.1%, and each layer of the thickness d of the high refractive index medium11-3 um, the relative refractive index difference delta 2 of the low-refractive-index medium is-0.18% -0.005%, and the thickness d of each layer of the low-refractive-index medium23-9 um, a period is formed by one layer of high refractive index medium and an adjacent layer of low refractive index medium, pure silica materials are arranged in regions outside the periodically arranged high and low refractive index medium, the diameter of a cladding of the optical fiber is 250-600 um, an inner coating of the optical fiber is low refractive index polymer, the relative refractive index difference delta 3 of the low refractive index polymer is less than or equal to-5%, the outer diameter of the optical fiber is 350-700 um, an outer coating of the optical fiber is high refractive index polymer, and the relative refractive index difference delta 4 of the high refractive index polymer is more than or equal to 3.5%The outer diameter of the steel tube is 500-800 um;
wherein, by
Figure FDA0003051647560000031
Determining the relative refractive index difference delta of the core, where ncoreIs the refractive index of the core, nSiIs a pure silicon refractive index;
by
Figure FDA0003051647560000032
Determining the relative refractive index difference Delta 1 of the high refractive index medium in the cladding, wherein nGeIs the refractive index of the high refractive index medium in the cladding;
by
Figure FDA0003051647560000033
Determining the relative refractive index difference Delta 2 of the low-refractive-index medium in the cladding, wherein nFThe refractive index of the low-refractive-index medium in the cladding;
by
Figure FDA0003051647560000034
Determining the relative refractive index difference Delta 3 of the inner coating of the optical fiber
Figure FDA0003051647560000035
Determining the relative refractive index difference Δ 4 of the outer coating of the optical fiber, wherein n3Is the refractive index of the inner coating of the optical fiber, n4Is the refractive index of the outer coating of the optical fiber.
6. A Bragg optical fiber as claimed in claim 5, wherein the relative refractive index difference Δ of the core is 0.085% to 0.19%, the relative refractive index difference Δ 1 of the high refractive index medium is 0.2% to 0.34%, the relative refractive index difference Δ 2 of the low refractive index medium is-0.06% to-0.02%, and the cladding of the optical fiber has 10 to 16 of said periods.
7. A method of preparing a bragg fiber, comprising:
drawing the optical fiber preform prepared by the preparation method of the Bragg optical fiber preform of claim 4 into a rare earth doped Bragg optical fiber with a cladding of 250-600 um, coating a low refractive index coating with a relative refractive index difference delta 3 being less than or equal to-5% to form an inner coating of the optical fiber, wherein the outer diameter of the inner coating is 350-700 um, coating a high refractive index coating with a relative refractive index difference delta 4 being greater than or equal to 3.5% to form an outer coating of the optical fiber, and the outer diameter of the outer coating is 500-800 um, wherein the optical fiber preform is prepared by coating a rare earth doped Bragg optical fiber with a relative
Figure FDA0003051647560000036
Determining the relative refractive index difference Delta 3 of the inner coating of the optical fiber
Figure FDA0003051647560000037
Determining the relative refractive index difference Δ 4 of the outer coating of the optical fiber, wherein n3Is the refractive index of the inner coating of the optical fiber, nSiIs a refractive index of pure silicon, n4Is the refractive index of the outer coating of the optical fiber.
8. Use of a bragg fiber according to any one of claims 5 or 6, comprising: the single-mode laser can be used as a gain medium or a transmission medium of the optical fiber laser to realize mode selection and obtain single-mode laser in the wavelength range of 1030 nm-1110 nm.
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