CN117706681A - Vortex optical broadband dispersion compensation optical fiber and preparation method thereof - Google Patents
Vortex optical broadband dispersion compensation optical fiber and preparation method thereof Download PDFInfo
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- 239000006185 dispersion Substances 0.000 title claims abstract description 113
- 239000013307 optical fiber Substances 0.000 title claims abstract description 113
- 230000003287 optical effect Effects 0.000 title claims abstract description 58
- 238000002360 preparation method Methods 0.000 title claims abstract description 12
- 239000000835 fiber Substances 0.000 claims abstract description 53
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 48
- 239000011162 core material Substances 0.000 claims description 27
- 239000000377 silicon dioxide Substances 0.000 claims description 24
- 230000008859 change Effects 0.000 claims description 20
- 235000012239 silicon dioxide Nutrition 0.000 claims description 20
- 239000000463 material Substances 0.000 claims description 18
- 238000009826 distribution Methods 0.000 claims description 17
- 239000011521 glass Substances 0.000 claims description 12
- 230000008878 coupling Effects 0.000 claims description 9
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- 238000005859 coupling reaction Methods 0.000 claims description 9
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- 238000013461 design Methods 0.000 claims description 8
- KRHYYFGTRYWZRS-UHFFFAOYSA-M Fluoride anion Chemical compound [F-] KRHYYFGTRYWZRS-UHFFFAOYSA-M 0.000 claims description 4
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 claims description 4
- 238000005253 cladding Methods 0.000 claims description 4
- 238000010438 heat treatment Methods 0.000 claims description 3
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 claims 1
- 239000003570 air Substances 0.000 claims 1
- 229910052731 fluorine Inorganic materials 0.000 claims 1
- 239000011737 fluorine Substances 0.000 claims 1
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- 238000010586 diagram Methods 0.000 description 7
- 238000004891 communication Methods 0.000 description 5
- 230000005540 biological transmission Effects 0.000 description 3
- 230000010287 polarization Effects 0.000 description 3
- 238000003860 storage Methods 0.000 description 3
- 238000004590 computer program Methods 0.000 description 2
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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
- G02B6/03616—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference
- G02B6/03661—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 4 layers only
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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
- G02B6/028—Optical fibres with cladding with or without a coating with core or cladding having graded refractive index
- G02B6/0283—Graded index region external to the central core segment, e.g. sloping layer or triangular or trapezoidal layer
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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
- G02B6/028—Optical fibres with cladding with or without a coating with core or cladding having graded refractive index
- G02B6/0283—Graded index region external to the central core segment, e.g. sloping layer or triangular or trapezoidal layer
- G02B6/0285—Graded index layer adjacent to the central core segment and ending at the outer cladding index
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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
- G02B6/24—Coupling light guides
- G02B6/255—Splicing of light guides, e.g. by fusion or bonding
- G02B6/2552—Splicing of light guides, e.g. by fusion or bonding reshaping or reforming of light guides for coupling using thermal heating, e.g. tapering, forming of a lens on light guide ends
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Abstract
The invention belongs to the technical field of optical fibers, and particularly discloses a vortex optical broadband dispersion compensation optical fiber and a preparation method thereof, wherein the broadband dispersion compensation optical fiber sequentially comprises a low refractive index fiber core, a first high refractive index annular region, a first low refractive index annular region, a second high refractive index annular region and a second low refractive index annular region from the center of the optical fiber outwards; the diameter of each region of the broadband dispersion compensation optical fiber is axially changed after the broadband dispersion compensation optical fiber is tapered; wherein: the first high refractive index annular region and the second high refractive index annular region each have a refractive index greater than the other regions. The invention realizes the compensation of positive dispersion in a broadband wavelength range and simplifies the structure of the optical fiber. The optical fiber has a relatively simple structure and is easy to draw and practically apply.
Description
Technical Field
The invention belongs to the technical field of optical fibers, and particularly relates to a vortex optical broadband dispersion compensation optical fiber and a preparation method thereof.
Background
Vortex rotation, with a twisted helical phase front, is considered an additional multiplexing method in the spatial domain, which can provide additional data channels in an information transmission system. The vortex rotation is divided into polarization vortex rotation and phase vortex rotation, the polarization vortex rotation is divided into radial vector beam TM 01 And an angular vector beam TE 01 Two modes are composed, phase vortex rotation is also called Orbital Angular Momentum (OAM) vortex rotation, and an l-order OAM mode is generated by linear combination of an odd mode and an even mode of an optical fiber eigenmode (EH or HE mode), and is as follows:
where l (=1, 2,3 …) represents a topological charge, m is an intensity distribution order in the radial direction corresponding to the mode, 'OAM' superscript '±' represents a circular polarization direction, and l < a > subscript '±' represents a wavefront rotation direction. The OAM modes of different orders are mutually orthogonal, which enables them to be multiplexed along the same optical axis and with low crosstalk. OAM may be a new degree of freedom for space division multiplexing techniques. Through thirty years of intensive research, the application of OAM light beams has been greatly expanded to the fields of light capturing, sensing, classical and quantum communication and the like.
Chromatic dispersion is an optical pulse broadening effect caused by the difference in group velocities of different wavelength components in the spectrum as they propagate in an optical fiber. Chromatic dispersion has been widely used in free space and fiber optic communication systems such as ultra high speed optical oscilloscopes, optical correlation, time lenses and optical buffers. In high-speed optical fiber communication systems, an increase in bit rate results in a narrowing of bit spacing, and an increase in linewidth of an externally modulated laser, thereby reducing dispersion tolerance. In order to balance the chromatic dispersion in optical systems, some studies have incorporated optical devices with opposite signs of chromatic dispersion, such as dispersion compensating fibers, optical phase conjugates, and fiber gratings, in the optical path to compensate for the chromatic dispersion. For dispersion accumulation in fiber-based optical communication systems, dispersion compensating fibers can minimize their adverse effects by negative dispersion compensating positive dispersion. Heretofore, fiber designs with large negative dispersion have been proposed, but the working window width is relatively narrow, the flexibility is poor, and it is difficult to apply to fiber communication systems on a large scale.
Disclosure of Invention
The invention provides a vortex optical broadband dispersion compensation optical fiber and a preparation method thereof, which aim to realize the compensation of positive dispersion in a broadband wavelength range and simplify the structure and manufacturing difficulty of the optical fiber.
The technical scheme adopted by the invention is as follows:
the invention provides a vortex optical broadband dispersion compensation optical fiber, which is characterized in that the cross section of the optical fiber sequentially comprises a low refractive index fiber core, a first high refractive index annular region, a first low refractive index annular region, a second high refractive index annular region and a second low refractive index annular region from the center of the optical fiber outwards; the diameters of all areas of the vortex optical broadband dispersion compensation optical fiber after the vortex optical broadband dispersion compensation optical fiber is tapered uniformly change along the axial direction; wherein: the refractive index of the first high refractive index annular region and the refractive index of the second high refractive index annular region are larger than those of other regions, and the refractive index distribution on the cross section of the optical fiber forms a double concentric annular shape.
As a further improvement of the present invention, the low refractive index core n 1 First high refractive index annular region n 2 First low refractive index annular region n 3 Second high refractive index annular region n 4 And a second low refractive index annular region emissivity n 5 Satisfy n 2 、n 4 The value of (2) is greater than n 1 、n 3 、n 5 Is a value of (2);
the first high-refractive-index annular region and the second high-refractive-index annular region select the same or different refractive index materials and proper refractive index distribution according to actual requirements, and the refractive index distribution is in step or gradual change.
As a further improvement of the invention, the low refractive index fiber core material is air, silicon dioxide, fluorine-doped silicon dioxide or Schott glass; the first low-refractive-index annular region and the second low-refractive-index annular region are made of silicon dioxide, fluorine-doped silicon dioxide and Schott glass; the materials of the first high refractive index annular region and the second high refractive index annular region are germanium-doped silicon dioxide, schott glass, fluoride and sulfide.
As a further improvement of the present invention, the low refractive index core radius r 1 A first high refractive index ringDistance r from outermost side of the shape region to center of the fiber 2 Distance r from outermost side of first low refractive index annular region to center of optical fiber 3 Distance r from outermost side of second high refractive index annular region to center of optical fiber 4 Radius r of optical fiber cladding 5 Satisfy r 1 ＜r 2 ＜r 3 ＜r 4 ＜r 5 。
As a further refinement of the invention, the modes transmitted in the first and second high refractive index annular regions are coupled to form a symmetric mode with negative dispersion and an anti-symmetric mode with positive dispersion.
As a further improvement of the invention, the change in optical field intensity of the optical fiber producing negative dispersion satisfies the following conditions: at wavelengths less than lambda 0 The intensity of the time light field is mainly distributed in the first high refractive index annular region; when the wavelength is equal to lambda 0 When the same mode refractive index in the first high refractive index annular region and the second high refractive index annular region is lambda 0 Near each other at the wavelength, the vortex mode has negative dispersion in a narrower range around that wavelength, where the optical field intensity is present in both the first and second high refractive index annular regions; when the wavelength is greater than lambda 0 When the optical field intensity is mainly distributed in the second high refractive index annular region.
As a further improvement of the invention, after the optical fiber is tapered, the structural parameters of the optical fiber at different axial positions are slowly changed, and the wavelength range of negative dispersion is also slowly and orderly changed; the flat broadband negative dispersion is realized by controlling the tapering speed or temperature.
As a further improvement of the invention, the vortex optical broadband dispersion compensation optical fiber adopts a symmetrical mode with negative dispersion; after the optical fiber is tapered, the structural parameters of the optical fiber at different axial positions are slowly changed, and the wavelength range of negative dispersion is also slowly and orderly changed; the flat broadband negative dispersion is realized by controlling the tapering speed or temperature.
The low-refractive-index fiber core is characterized in that the first low-refractive-index annular region and the second low-refractive-index annular region are made of silicon dioxide, the first high-refractive-index annular region and the second high-refractive-index annular region are made of germanium-doped silicon dioxide, and the germanium-doped molar concentration of the first high-refractive-index annular region and the second high-refractive-index annular region is 40mol%.
As a further improvement of the present invention, the low refractive index core, the first low refractive index annular region and the second low refractive index annular region are each internally provided with air holes periodically arranged.
As a further improvement of the invention, a third high refractive index annular region and a third low refractive index annular region are also arranged outside the second low refractive index annular region in sequence; mode coupling occurs between the first high refractive index annular region and the second high refractive index annular region when the vortex rotation is incident from the first high refractive index annular region, and mode coupling occurs between the second high refractive index annular region and the third high refractive index annular region when the vortex rotation is incident from the third high refractive index annular region.
In a second aspect, the present invention provides a method for preparing a vortex optical broadband dispersion compensating fiber, comprising:
determining optical fiber materials and structural parameters before tapering according to the required negative dispersion value and a working window;
obtaining narrow-band negative dispersion curves of optical fibers at different cross sections after tapering;
based on the dispersion curve, designing a tapered optical fiber axial diameter change curve to realize the required broadband negative dispersion;
and (5) performing preparation of the preform and drawing and tapering of the optical fiber according to the design parameters.
As a further improvement of the invention, the axial diameter change curve of the optical fiber after tapering is used for controlling the positive and negative of the dispersion slope of the dispersion flat area.
As a further improvement of the invention, the preparation of the preformed rod and the drawing of the optical fiber are carried out according to design parameters, and the tapering speed and the heating temperature are controlled, thereby realizing the vortex optical broadband dispersion compensation optical fiber.
Compared with the prior art, the invention has the advantages and beneficial effects that:
the invention can realize the adjustment of the size, the slope and the wavelength range of the broadband negative dispersion by selecting the materials of the fiber core and the annular region and the refractive index distribution, properly adjusting the thickness or the position of the annular region and controlling the tapering speed and the temperature. The diameter of the optical fiber before tapering is close to that of the single-mode optical fiber, so that the matching of the core diameter and the mode field of the front-end single-mode optical fiber is facilitated, and the coupling loss of the front-end single-mode optical fiber is reduced. The optical fiber has a relatively simple structure, is suitable for vortex light stable transmission, and is easy to draw and practical application. The invention realizes the compensation of positive dispersion in a broadband wavelength range and simplifies the structure of the optical fiber. The optical fiber has a relatively simple structure and is easy to draw and practically apply.
Drawings
FIG. 1 is a schematic diagram of the structure of a vortex optical broadband dispersion compensating fiber of the present invention along the axial fiber diameter variation; wherein the A-B region is a tapered region;
FIG. 2 is a schematic diagram of a cross-sectional structure and refractive index profile of an optical fiber according to the present invention;
FIG. 3 is a flow chart of the present invention;
FIG. 4 is a graph showing the change in optical field intensity during the process of producing negative dispersion in an optical fiber according to the present invention;
FIG. 5 is a graph of narrow band negative dispersion of the fiber of the present invention at axially different cross sections from A to B in FIG. 1;
FIG. 6 is a graph of broadband flat negative dispersion for an optical fiber of the present invention;
FIG. 7 is a schematic diagram of positive and negative slope adjustability of a flat negative dispersion region of an optical fiber in accordance with the present invention;
FIG. 8 is a schematic diagram of a second embodiment of a vortex optical broadband dispersion compensating fiber with a diameter variation along the axial direction of the fiber;
FIG. 9 is a schematic cross-sectional view of an optical fiber having three concentric rings.
Detailed Description
In order to make the technical solution of the present invention better understood by those skilled in the art, the technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, shall fall within the scope of the invention.
A first object of the present invention, as shown in fig. 1, is to provide a vortex optical broadband dispersion compensating fiber, which aims to achieve compensation of positive dispersion in a broadband wavelength range and to simplify the fiber structure and manufacturing difficulty.
The optical fiber cross section comprises a low refractive index fiber core, a first high refractive index annular region, a first low refractive index annular region, a second high refractive index annular region and a second low refractive index annular region from the center of the optical fiber outwards in sequence; the diameters of all areas of the vortex optical broadband dispersion compensation optical fiber after the vortex optical broadband dispersion compensation optical fiber is tapered uniformly change along the axial direction; wherein: the first high refractive index annular region and the second high refractive index annular region have refractive indexes larger than those of other regions, and the refractive index distribution on the cross section of the optical fiber forms a double-ring shape.
FIG. 1 is a schematic diagram of the structure of a vortex optical broadband dispersion compensating fiber of the present invention along the axial fiber diameter variation. Wherein the a-B region is a tapered region. The vortex optical broadband dispersion compensation optical fiber sequentially comprises a low refractive index fiber core, a first high refractive index annular region, a first low refractive index annular region, a second high refractive index annular region and a second low refractive index annular region from the center of the optical fiber to the outside, wherein the diameters of all regions of the optical fiber are changed along the axial direction after tapering.
Wherein: the low refractive index core, the first high refractive index annular region, the first low refractive index annular region, the second high refractive index annular region, and the second low refractive index annular region index n 1 、n 2 、n 3 、n 4 、n 5 Satisfy n between 2 、n 4 The value of (2) is greater than n 1 、n 3 、n 5 I.e. the first high refractive index annular region and the second high refractive index annular region each have a refractive index greater than the other regions.
The first high refractive index annular region and the second high refractive index annular region can be made of materials with the same or different refractive indexes according to actual requirements, and the refractive index distribution of the materials can be in step or gradual change distribution. The low refractive index fiber core material is air, silicon dioxide, fluorine-doped silicon dioxide, schott glass or the like; the first low refractive index annular region and the second low refractive index annular region are made of silicon dioxide, fluorine-doped silicon dioxide, schott glass and the like; the materials of the first high refractive index annular region and the second high refractive index annular region are germanium-doped silicon dioxide, schott glass, fluoride, sulfide and the like; the diameter of each region of the optical fiber can be controlled by the preparation temperature, the tapering speed and the like along the axial direction.
In this configuration, since the first and second high refractive index annular regions have higher refractive indices than the other regions, modes are confined to transmission within the first and second high refractive index annular regions, and the effective refractive index of the modes in the first high refractive index annular region decreases with wavelength faster than the effective refractive index in the second high refractive index annular region, under certain refractive index contrast and structural parameters, the refractive indices of the same modes in the two regions approach each other at a wavelength at which strong mode coupling occurs, resulting in a composite mode, i.e., a symmetric mode having negative dispersion in a narrower range around the wavelength and an antisymmetric mode having positive dispersion in this wavelength range.
The vortex optical broadband dispersion compensation optical fiber adopts a symmetrical mode with negative dispersion. After the optical fiber is tapered, the structural parameters of the optical fiber at different axial positions are slowly changed, the wavelength range of negative dispersion is also slowly and orderly changed, the wavelength range of negative dispersion is enlarged, and flat broadband negative dispersion can be realized by controlling the tapered speed or temperature.
As shown in fig. 2, the low refractive index core radius r 1 Distance r from outermost side of first high refractive index annular region to center of optical fiber 2 Distance r from outermost side of first low refractive index annular region to center of optical fiber 3 Distance r from outermost side of second high refractive index annular region to center of optical fiber 4 Radius r of optical fiber cladding 5 Satisfy r 1 ＜r 2 ＜r 3 ＜r 4 ＜r 5 。
A second object of the present invention is to provide a flow chart of a vortex optical broadband dispersion compensating fiber design, as shown in fig. 3.
Designing optical fiber materials and structural parameters before tapering according to the required negative dispersion value and a working window;
obtaining narrow-band negative dispersion curves of optical fibers at different cross sections after tapering;
based on the dispersion curve, designing a tapered optical fiber axial diameter change curve to realize the required broadband negative dispersion; and finally, preparing a preform and drawing and tapering the optical fiber according to the design parameters.
The method specifically comprises the following steps:
step one: the cross section structure of the optical fiber is shown in figure 2 and comprises a low refractive index fiber core, a first high refractive index annular region, a first low refractive index annular region, a second high refractive index annular region and a second low refractive index annular region from inside to outside, wherein the refractive indexes of the second high refractive index annular region and the second low refractive index annular region are respectively n 1 、n 2 、n 3 、n 4 、n 5 The refractive index of the first high-refractive-index annular region and the second high-refractive-index annular region is larger than that of other regions, the first high-refractive-index annular region and the second high-refractive-index annular region can be made of materials with the same or different refractive indexes according to actual requirements, the refractive index distribution of the materials can be in step or gradual change distribution, and the low-refractive-index fiber core material is air, silicon dioxide, fluorine-doped silicon dioxide, schott glass or the like; the first low refractive index annular region and the second low refractive index annular region are made of silicon dioxide, fluorine-doped silicon dioxide, schott glass and the like; the materials of the first high refractive index annular region and the second high refractive index annular region are germanium-doped silicon dioxide, schott glass, fluoride, sulfide and the like.
In this embodiment, the low refractive index core, the first low refractive index annular region and the second low refractive index annular region are made of silica, the first high refractive index annular region and the second high refractive index annular region are made of germanium-doped silica, and the germanium-doped molar concentration of the first high refractive index annular region and the second high refractive index annular region is 40mol%.
FIG. 2 is a schematic view of the cross-sectional structure and refractive index distribution of an optical fiber according to the present inventionA drawing. The left side of fig. 2 is a schematic cross-sectional view of the optical fiber. The black and gray regions correspond to high refractive index materials, the black region has a higher refractive index than the gray region, the white region corresponds to low refractive index materials, the first high refractive index annular region and the second high refractive index annular region can be made of the same or different refractive index materials and appropriate refractive index distribution according to actual requirements, and gradient refractive index distribution is shown in the figure. The refractive index profile of the fiber structure is given by the right graph of fig. 2. Wherein r is 1 Is the radius of the low refractive index fiber core, r 2 R is the distance from the outermost side of the first high refractive index annular region to the center of the optical fiber 3 R is the distance from the outermost side of the first low refractive index annular region to the center of the optical fiber 4 R is the distance from the outermost side of the second high refractive index annular region to the center of the optical fiber 5 The parameters of the radius of the fiber cladding can be selected according to the coupling requirement of the front-end fiber.
FIG. 4 is a graph showing the negative dispersion produced by the fiber of the present invention and the change in optical field intensity during this process. At wavelengths less than lambda 0 The intensity of the time light field is mainly distributed in the first high refractive index annular region; when the wavelength is equal to lambda 0 The refractive index of the same mode in the two regions is lambda 0 Near each other at the wavelength, the vortex mode has negative dispersion in a narrower range around that wavelength, as shown in the upper side of fig. 4, when the optical field intensity is present in both the first and second high refractive index annular regions; when the wavelength is greater than lambda 0 When the optical field intensity is mainly distributed in the second high refractive index annular region. The lower side of FIG. 4 shows that the light field intensity is less than lambda throughout 0 Equal to lambda 0 And greater than lambda 0 Distribution diagram of time.
Step two: calculating structural parameter r 1 ＝0.6μm，r 2 ＝1.8μm，r 3 ＝12μm，r 4 ＝12.4μm，r 4 OAM at axially different cross sections after fiber tapering of =62.5 μm 1,1 The mode narrow band negative dispersion curve is shown in fig. 5, the dispersion curves sequentially correspond to the parameters of the optical fibers at different axial cross sections from A to B in fig. 1 from right to left, and the negative dispersion values and the change order of the wavelength ranges can be seen from the graph.
Fig. 5 is a graph of narrow band negative dispersion of an optical fiber of the present invention at axially different cross sections a through B in fig. 1.
FIG. 6 is a graph of broadband flat negative dispersion for an optical fiber of the present invention.
Step three: the axial diameter change curve of the optical fiber after tapering is designed based on the dispersion curve, so that the broadband flat negative dispersion shown in fig. 6 is realized. According to the actual requirements, as shown in fig. 7, the positive and negative of the dispersion curve slope of the dispersion flat area can be controlled by adjusting the axial diameter change curve of the optical fiber after tapering, so that the method has wider application prospect.
FIG. 7 is a schematic diagram of the positive and negative slope adjustment of a flat negative dispersion region of an optical fiber according to the present invention. Wherein the slope of the dotted line is positive, the slope of the solid line is close to 0, and the slope of the dotted line is negative.
Step four: and (3) performing preparation of the preform and drawing of the optical fiber according to design parameters, and controlling the tapering speed and the heating temperature to realize the vortex optical broadband dispersion compensation optical fiber.
In addition, the fiber may be radially realized by introducing periodically arranged air holes to achieve a relatively low refractive index core and annular regions, two relatively high refractive index annular regions being shaded in FIG. 8, while the refractive index of the two high refractive index annular regions may be further adjusted by changing the arrangement and number of air holes or by using a high refractive index material. The optical fiber comprises a low refractive index fiber core 1, a first high refractive index annular region 2, a first low refractive index annular region 3, a second high refractive index annular region 4 and a second low refractive index annular region 5 from the center of the optical fiber outwards in sequence; in particular, the low refractive index core, the first low refractive index annular region and the second low refractive index annular region each have air holes 10 periodically arranged therein. The working principle is the same as that of the vortex optical broadband dispersion compensation optical fiber, and the diameters of all areas of the optical fiber are uniformly changed along the axial direction after the optical fiber is tapered, so that the vortex optical broadband dispersion compensation optical fiber is realized.
Due to the profile similar to the vortex mode, the ring core fiber has considerable scalability. Multiple concentric high refractive index annular regions may be further cascaded into the fiber to provide multiple selectable working windows for the vortex mode. FIG. 9 is a cross-section of an optical fiber having three concentric rings, the cross-section of the optical fiber including, in order from the center of the optical fiber, a low refractive index core 1, a first high refractive index annular region 2, a first low refractive index annular region 3, a second high refractive index annular region 4, a second low refractive index annular region 5, a third high refractive index annular region 6, and a third low refractive index annular region 7; when light carrying vortex modes is launched into the fiber from the first high refractive index annular region, mode coupling occurs between the first high refractive index annular region and the second high refractive index annular region, and large negative dispersion occurs. When the light beam enters the optical fiber through the third high refractive index annular region, a large negative dispersion occurs due to the coupling between the second high refractive index annular region and the third high refractive index annular region. After tapering, the diameters of all regions of the optical fiber change uniformly along the axial direction, negative dispersion changes slowly and orderly, vortex light enters from different annular regions, and vortex optical rotation broadband dispersion compensation can be realized in different wavelength ranges. The high index annular region may be further increased to provide more selectable working windows for the vortex mode.
It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
While the invention has been described with reference to certain preferred embodiments, it will be understood by those skilled in the art that various changes and substitutions may be made without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the protection scope of the invention is subject to the protection scope of the claims.
Claims (10)
1. The vortex optical broadband dispersion compensation optical fiber is characterized in that the cross section of the optical fiber sequentially comprises a low refractive index fiber core, a first high refractive index annular region, a first low refractive index annular region, a second high refractive index annular region and a second low refractive index annular region from the center of the optical fiber outwards; the diameters of all areas of the vortex optical broadband dispersion compensation optical fiber after the vortex optical broadband dispersion compensation optical fiber is tapered uniformly change along the axial direction; wherein: the refractive index of the first high refractive index annular region and the refractive index of the second high refractive index annular region are larger than those of other regions, and the refractive index distribution on the cross section of the optical fiber forms a double concentric annular shape.
2. The vortex optical broadband dispersion compensating fiber of claim 1 wherein the low refractive index core n 1 First high refractive index annular region n 2 First low refractive index annular region n 3 Second high refractive index annular region n 4 And a second low refractive index annular region emissivity n 5 Satisfy n 2 、n 4 The value of (2) is greater than n 1 、n 3 、n 5 Is a value of (2);
the first high-refractive-index annular region and the second high-refractive-index annular region select the same or different refractive index materials and proper refractive index distribution according to actual requirements, and the refractive index distribution is in step or gradual change.
3. The vortex optical broadband dispersion compensating fiber of claim 1 wherein the low refractive index core material is air, silica, fluorine doped silica, schott glass; the first low-refractive-index annular region and the second low-refractive-index annular region are made of silicon dioxide, fluorine-doped silicon dioxide and Schott glass; the materials of the first high refractive index annular region and the second high refractive index annular region are germanium-doped silicon dioxide, schott glass, fluoride and sulfide.
4. The vortex optical broadband dispersion compensating fiber of claim 1 wherein the low refractive index core radius r 1 Distance r from outermost side of first high refractive index annular region to center of optical fiber 2 Distance r from outermost side of first low refractive index annular region to center of optical fiber 3 Distance r from outermost side of second high refractive index annular region to center of optical fiber 4 Radius r of optical fiber cladding 5 Satisfy r 1 ＜r 2 ＜r 3 ＜r 4 ＜r 5 。
5. The vortex optical broadband dispersion compensating fiber of claim 1 wherein the modes transmitted in the first high refractive index annular region and the second high refractive index annular region are coupled to form a symmetric mode and an anti-symmetric mode, the symmetric mode having negative dispersion and the anti-symmetric mode having positive dispersion;
the change in optical field intensity of the fiber producing negative dispersion satisfies the following conditions: at wavelengths less than lambda 0 The intensity of the time light field is mainly distributed in the first high refractive index annular region; when the wavelength is equal to lambda 0 When the same mode refractive index in the first high refractive index annular region and the second high refractive index annular region is lambda 0 Near each other at the wavelength, the vortex mode has negative dispersion in a narrower range around that wavelength, where the optical field intensity is present in both the first and second high refractive index annular regions; when the wavelength is greater than lambda 0 When the optical field intensity is mainly distributed in the second high refractive index annular region.
6. The vortex optical broadband dispersion compensating fiber according to claim 1, wherein after the fiber is tapered, the structural parameters of the fiber at different axial positions are slowly changed, and the wavelength range of negative dispersion is also slowly and orderly changed; the flat broadband negative dispersion is realized by controlling the tapering speed or temperature.
7. The vortex optical broadband dispersion compensating fiber of claim 1 or 2 wherein the low refractive index core, the first low refractive index annular region and the second low refractive index annular region each have air holes periodically arranged therein.
8. The vortex optical broadband dispersion compensating fiber according to claim 1 or 2, wherein a third high refractive index annular region and a third low refractive index annular region are further provided in sequence outside the second low refractive index annular region; mode coupling occurs between the first high refractive index annular region and the second high refractive index annular region when the vortex rotation is incident from the first high refractive index annular region, and mode coupling occurs between the second high refractive index annular region and the third high refractive index annular region when the vortex rotation is incident from the third high refractive index annular region.
9. The preparation method of the vortex optical broadband dispersion compensation optical fiber is characterized by comprising the following steps of:
determining optical fiber materials and structural parameters before tapering according to the required negative dispersion value and a working window;
obtaining narrow-band negative dispersion curves of optical fibers at different cross sections after tapering;
based on the dispersion curve, designing a tapered optical fiber axial diameter change curve to realize the required broadband negative dispersion;
and (5) performing preparation of the preform and drawing and tapering of the optical fiber according to the design parameters.
10. The method for preparing a vortex optical broadband dispersion compensating fiber according to claim 9, wherein the axial diameter change curve of the fiber after tapering controls the positive and negative of the dispersion curve slope in the dispersion flattening area; and (3) performing preparation of the preform and drawing of the optical fiber according to design parameters, and controlling the tapering speed and the heating temperature to obtain the vortex optical broadband dispersion compensation optical fiber.
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