All-solid-state large-mode-field single-mode optical fiber

Abstract

The invention relates to the technical field of optical fiber design, in particular to an all-solid-state large-mode-field single-mode optical fiber. A fiber core is a medium round rod; the cladding comprises a plurality of micro-structure units and a substrate, the substrate is filled between the fiber core and the micro-structure units, each micro-structure unit is composed of a high-refractive-index medium tube and a low-refractive-index medium rod from outside to inside, and the micro-structure units are arranged by taking the fiber core as a symmetric center. By adjusting structural parameters, an effective refractive index curve of a fiber core high-order mode can be positioned in an effective refractive index band of a cladding mode, so that the effective refractive index of the fiber core high-order mode is equal to that of the cladding mode, the fiber core high-order mode has a high-loss characteristic, the effective refractive index value of a fiber core fundamental mode is far higher than that of the cladding mode, the fiber core fundamental mode can keep ultralow loss, and the fiber core can be used for optical fiber communication. When the size of the fiber core is large, the purpose of single-mode transmission is achieved. The optical fiber has excellent characteristics in the aspects of high-power laser generation and transmission and low bending loss, and provides a high-quality transmission medium for optical transmission.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber design, and in particular to an all-solid-state large mode field single-mode optical fiber. Background Art

[0002] With the advancement of technology, researchers hope to increase the capacity of fiber-optic communication systems by increasing the transmission channels of dense wavelength division multiplexing (DWDM). However, increasing the transmission channels will reduce the channel spacing. This communication system is susceptible to the nonlinear effects of optical fibers, especially the Raman effect, which leads to signal distortion during high-speed transmission. In addition, the output power of fiber lasers is constantly increasing. In lasers, the increase in power will also cause nonlinear effects of optical fibers. For optical fibers, the nonlinear effect is inversely proportional to the mode field area of ​​the optical fiber. The larger the mode field area of ​​the optical fiber, the weaker the nonlinear effect. Therefore, large mode field optical fibers can effectively reduce nonlinear effects and increase the nonlinear threshold of optical fibers. In order to achieve the large mode field characteristics of optical fibers, it is necessary to increase the core diameter. However, increasing the core diameter of optical fibers will cause the existence of multiple transverse modes, which will have an adverse effect on the quality of the output beam. Therefore, in order to ensure the quality of the output light, while achieving a large mode field of optical fibers, it is required that the optical fiber can achieve single-mode operation.

[0003] Therefore, it is urgent to research and develop a large mode field low loss optical fiber that can increase the core diameter or increase the refractive index difference between the core and the cladding while still maintaining the single-mode characteristics. Summary of the invention

[0004] The present invention aims to at least improve one of the technical problems existing in the prior art. To this end, the present invention proposes an all-solid-state large mode field single-mode optical fiber.

[0005] The all-solid-state large mode field single-mode optical fiber according to the first aspect of the present invention comprises: A fiber core, which is located at the center of the optical fiber and is a dielectric round rod; The cladding comprises a plurality of microstructure units and a substrate, wherein the microstructure units are arranged symmetrically with the fiber core as the center, and the substrate is filled between the fiber core and the microstructure units, wherein: The microstructure unit is composed of a dielectric tube and a dielectric rod. The refractive index of the dielectric tube is n 3 is greater than the refractive index of the dielectric rod n 4.

[0006] In a possible implementation of the first aspect, the core radius R0 of the optical fiber is greater than 15 μm, and the normalized parameter Much larger than 2.405, among which, n 1 is the refractive index of the fiber core, n 2 is the refractive index of the substrate, R0 is the radius of the core, λThe larger the core size, the greater the mode area.

[0007] In a possible implementation manner of the first aspect, the microstructure unit is tangential to or separated from the fiber core; When separated, the shortest distance between the edge of the core and the edge of the microstructure unit should be of the order of the operating wavelength to ensure effective coupling of the core high-order mode with the cladding mode, thereby filtering out the core high-order mode.

[0008] In a possible implementation manner of the first aspect, a cross-section of the medium pipe includes a circular ring shape or an elliptical ring shape.

[0009] In a possible implementation manner of the first aspect, a cross section of the dielectric rod may be circular or elliptical.

[0010] In a possible implementation manner of the first aspect, the positional relationship between the dielectric tube and the dielectric rod includes concentricity or non-concentricity.

[0011] In a possible implementation manner of the first aspect, the plurality of microstructure units are arranged at equal intervals with the fiber core as a symmetric center; The connecting lines between the center points of the microstructure units form a regular polygon, and the fiber core is located at the center of the regular polygon, ensuring that the structure is highly symmetrical so that the effective refractive indexes of the x polarization mode and the y polarization mode are equal.

[0012] In a possible implementation manner of the first aspect, the microstructure units can be arranged in a single layer.

[0013] In a possible implementation manner of the first aspect, the number N of the microstructure units is 2, 3, 4, 5, 6, 7, or 8.

[0014] In a possible implementation manner of the first aspect, the refractive index of the dielectric tube is n 3 is greater than the substrate refractive index n 2.

[0015] According to the all-solid-state large mode field single-mode optical fiber of the embodiment of the present invention, the optical fiber comprises a core region with a high refractive index (i.e., the refractive index of silica + Δ) and a cladding region containing an arrangement of microstructure units. The cladding mode in the optical fiber cladding has a large loss, and the effective refractive index of the cladding mode forms an effective refractive index band of the cladding mode.

[0016] Increasing the core diameter can achieve the large mode field characteristics of the optical fiber, reduce the energy of light per unit area, and avoid the adverse effects of nonlinear effects on optical fiber applications. The patent of this invention requires that the core radius R0 be greater than 15μm to achieve a large mode field, but this will cause the normalized frequency to be much greater than 2.405, thereby causing the existence of high-order modes in the core, thereby reducing the beam quality in the optical fiber.

[0017] In addition, increasing the refractive index difference between the optical fiber core and the cladding will also lead to the existence of higher-order modes in the core, thereby reducing the beam quality in the optical fiber.

[0018] The optical fiber structure of the present invention can increase the effective refractive index of the cladding mode in the high refractive index medium tube by increasing the value of R1 or t, so that the effective refractive index curve of the core high-order mode is in the effective refractive index band of the cladding mode, thereby achieving phase matching between the core high-order mode and the cladding mode, so the core high-order mode has a high loss characteristic, and the effective refractive index value of the core fundamental mode is much higher than that of the cladding mode, so the core fundamental mode can maintain ultra-low loss, and the purpose of single-mode transmission is achieved when the core size is large. All units of the optical fiber are circular, and the shape invariance is maintained when the optical fiber is drawn.

[0019] The optical fiber of the present invention can obtain the single-mode characteristics of the optical fiber by increasing the refractive index difference between the optical fiber core and the cladding or increasing the core diameter. Therefore, the optical fiber has excellent characteristics in high-power laser generation, transmission and low bending loss, providing a high-quality transmission medium for optical transmission.

[0020] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 A schematic diagram of the cross-sectional structure of an all-solid-state large mode field single-mode optical fiber provided in Example 1 of the present invention; Figure 2 The curve showing the variation of limiting loss of the all-solid-state large mode field single-mode optical fiber with respect to d1 provided in Example 1 of the present invention; Figure 3 The curve showing the change of the loss ratio of the high-order mode to the fundamental mode of the all-solid-state large mode field single-mode optical fiber as a function of d1 provided in Example 1 of the present invention; Figure 4 A curve showing the variation of the fundamental mode mode field area of ​​the all-solid-state large mode field single-mode optical fiber provided in Example 1 of the present invention with respect to d1; Figure 5 The bending loss curve of the all-solid-state large mode field single-mode optical fiber provided in Example 1 of the present invention varies with d1; Figure 6 A schematic diagram of the cross-sectional structure of an all-solid-state single-mode optical fiber provided in Embodiment 2 of the present invention; Figure 7 This is a schematic diagram of the cross-sectional structure of an all-solid-state single-mode optical fiber provided in Example 3 of the present invention.

[0023] Reference numerals: The fiber core 100 , the cladding 200 , the dielectric tube 210 , the dielectric rod 220 , and the substrate 230 . DETAILED DESCRIPTION

[0024] The embodiments of the present invention are described in detail below. The embodiments described with reference to the accompanying drawings are exemplary. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0025] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may be an intermediate element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an intermediate element at the same time.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0027] The terms "first", "second", "third", etc. in the specification and claims of the present application and the drawings are used to distinguish different objects rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a series of steps or units are included, or optionally, steps or units not listed are included, or optionally, other steps or units inherent to these processes, methods, products or devices are included.

[0028] Only the part relevant to the present application is shown in the accompanying drawings, but not all of the content. Before discussing the exemplary embodiments in more detail, it should be mentioned that some exemplary embodiments are described as processing or methods depicted as flow charts. Although the flow chart describes each operation (or step) as a sequential process, many of the operations therein can be implemented in parallel, concurrently or simultaneously. In addition, the order of each operation can be rearranged. When its operation is completed, the process can be terminated, but it can also have additional steps not included in the accompanying drawings. The process can correspond to a method, function, procedure, subroutine, subprogram, etc.

[0029] The terms "component", "module", "system", "unit", etc. used in this specification are used to represent computer-related entities, hardware, firmware, a combination of hardware and software, software, or software in execution. For example, a unit can be, but is not limited to, a process running on a processor, a processor, an object, an executable file, an execution thread, a program, and / or distributed between two or more computers. In addition, these units can be executed from various computer-readable media having various data structures stored thereon. Units can communicate through local and / or remote processes, for example, based on signals having one or more data packets (e.g., data from a second unit interacting with another unit in a local system, a distributed system, and / or a network. For example, the Internet interacts with other systems via signals).

[0030] Example 1 This embodiment provides an all-solid-state large mode field single-mode optical fiber, which includes: A fiber core 100, which is located at the center of the optical fiber and is a dielectric round rod; The cladding 200 includes a plurality of microstructure units and a substrate 230, wherein the microstructure units are arranged with the core 100 as the symmetric center, and the substrate 230 is filled between the core 100 and the microstructure units, wherein: The microstructure unit is composed of a dielectric tube 210 and a dielectric rod 220 .

[0031] It should be noted that the material of the cladding region is any one of silicon dioxide, soft glass or plastic.

[0032] It should be noted that the core radius R0 of the optical fiber is greater than 15 μm, and the normalized parameter Much larger than 2.405, among which, n 1 is the refractive index of the core 100, n 2 is the refractive index of the substrate 230, R0 is the radius of the core 100, λ is the operating wavelength.

[0033] It should be noted that the microstructure unit is tangential to or separated from the fiber core 100; When separated, the shortest distance between the edge of the fiber core 100 and the edge of the microstructure unit should be of the order of the operating wavelength.

[0034] It should be noted that the shortest distance between the edge of the fiber core 100 and the edge of the microstructure unit refers to the distance between the outer edge of the fiber core 100 and the edge of the microstructure unit close to the fiber core.

[0035] It should be noted that the cross section of the medium pipe 210 includes a circular ring shape or an elliptical ring shape.

[0036] It should be noted that the cross section of the dielectric rod 220 may be circular or elliptical.

[0037] It should be noted that the positional relationship between the dielectric tube 210 and the dielectric rod 220 may be concentric or non-concentric.

[0038] It should be noted that the plurality of microstructure units are arranged at equal intervals with the fiber core 100 as the symmetric center; The connecting lines between the center points of the microstructure units form a regular polygon, and the fiber core is located at the center of the regular polygon.

[0039] It should be noted that the microstructure units can be arranged in a single layer.

[0040] It should be noted that the refractive index of the medium tube 210 is n 3 is greater than the refractive index of the substrate 230 n 2.

[0041] According to the all-solid-state large mode field single-mode optical fiber of the embodiment of the present invention, the optical fiber includes a core region with a high refractive index and a cladding region containing an arrangement of microstructure units. The cladding mode in the optical fiber cladding has a large loss, and the effective refractive index of the cladding mode forms an effective refractive index band of the cladding mode. By adjusting the structural parameters, the effective refractive index curve of the core high-order mode can be placed in the cladding mode effective refractive index band, thereby achieving phase matching between the core high-order mode and the cladding mode, that is, the effective refractive index is equal. Therefore, the core high-order mode has a high loss characteristic, and the effective refractive index value of the core fundamental mode is much higher than that of the cladding mode. Therefore, the core fundamental mode can maintain ultra-low loss, and the purpose of single-mode transmission is achieved when the core size is large. All subunits of the optical fiber are circular, and the shape invariance is maintained when the optical fiber is drawn.

[0042] Increasing the core diameter can achieve the large mode field characteristics of the optical fiber, reduce the energy of light per unit area, and avoid the adverse effects of nonlinear effects on optical fiber applications. Increasing the refractive index difference between the optical fiber core and the cladding or increasing the core diameter will cause the existence of transverse modes, thereby reducing the light beam quality in the optical fiber. The optical fiber of the present invention can obtain the single-mode characteristics of the optical fiber when increasing the refractive index difference between the optical fiber core and the cladding or increasing the core diameter. Therefore, the optical fiber has excellent characteristics in high-power laser generation, transmission and low bending loss, providing a high-quality transmission medium for light transmission.

[0043] In this embodiment, an implementation example in which the number of microstructure units is 3 is provided, wherein the dielectric tube 210 and the dielectric rod 220 have the same center, such as Figure 1 As shown, The radius R0 of the fiber core 100 is 20 μm, the thickness t and the outer radius R1 of the dielectric tube 210 are 4.5 μm and 19 μm respectively, the fiber core 100 and the dielectric tube 210 are separated by a distance d1=3 μm, and the dielectric tube 210 and the outer edge of the optical fiber are separated by a distance d2=2 μm. The refractive index of the material of the fiber core 100 and the dielectric tube 210 is n 1 and n 3 are 1.4521 and 1.4533 respectively, and the refractive index of the dielectric rod 220 and the substrate 230 is equal, that is, n 4= n 2=1.4497.

[0044] The finite element method is used to perform numerical simulation and theoretical analysis. The simulation results of the limiting loss of the optical fiber in a straight line with the distance d1 and d2 are shown in Figure 2 As shown, the fundamental mode loss is 10 -6 ~10 -3 In the order of magnitude range, the minimum loss is 1.15×10 -6 dB / m, the maximum loss is 3.78×10 -3 dB / m. When d1 is in the range of 0μm to 4μm, and d2 is less than or equal to 2μm, the high-order mode is greater than 1dB / m. Its loss is as follows Figure 3 As shown, the maximum can reach 10 -5 The mode field area changes as Figure 4 It can be seen that the mode field area decreases with the increase of d1, but it is greater than 700μm 2 , and d2 has little effect on the change of mode field area. It is generally believed that when the fundamental mode is less than 0.1dB / m and the high-order mode is greater than 1dB / m, it can be considered as single-mode transmission. When the parameters d1=4μm and d2=3μm, the fundamental mode is 8.11×10 -6 dB / m, the high-order mode is 1.27dB / m, the optical fiber has good single-mode characteristics, and the loss ratio is 1.57×10 5 , the mode field area is 732μm 2 When the fiber bending radius is 30cm, the simulation results are as follows: Figure 5 When d1 is greater than or equal to 3μm, the fundamental mode can reach less than 0.1dB / m and the high-order mode is greater than 1dB / m. It can be considered that single-mode transmission is achieved. When d1 and d2 are 4μm and 3μm respectively, the fundamental mode is only 0.02dB / m and the high-order mode is 4.06dB / m.

[0045] It can be seen that the large mode field optical fiber of the present invention can obtain the single-mode characteristics of the optical fiber by increasing the refractive index difference between the optical fiber core and the cladding or increasing the core diameter. Therefore, the optical fiber has excellent characteristics in high-power laser generation, transmission and low bending loss, providing a high-quality transmission medium for optical transmission.

[0046] Example 2 This embodiment provides another all-solid-state large mode field single-mode optical fiber, such as Figure 6 The cross section of the optical fiber is shown in Figure 1 As shown, the optical fiber is composed of a core 100, a dielectric tube 210, a dielectric rod 220 and a substrate 230, and the dielectric tube 210 and the dielectric rod 220 have the same center. The core 100 is the core, which is located at the center of the optical fiber. The dielectric tube 210, the dielectric rod 220 and the substrate 230 are the cladding of the optical fiber. The dielectric tube 210 and the dielectric rod 220 constitute microstructure units in the optical fiber cladding, and these microstructure units are arranged with the core as the symmetric center, and the number of microstructure units N=4. The material of the cladding area is any one of silica, soft glass or plastic.

[0047] When the parameters R1=20μm, R1=19μm, t=4.5μm, d1=3μm, d2=2μm, the fundamental mode is 7.08×10 -5 dB / m, the high-order mode is 2.26dB / m, the optical fiber has good single-mode characteristics, and the loss ratio is 3.19×10 4 , the mode field area is 744μm 2 When the fiber bending radius is 33cm, the fundamental mode is only 0.072dB / m and the high-order mode is 7.42dB / m, which can be considered to achieve single-mode transmission.

[0048] Example 3 The present invention discloses a fully solid large mode field single mode optical fiber, the cross section of which is as follows: Figure 7 As shown, the optical fiber is composed of a core 100, a dielectric tube 210, a dielectric rod 220 and a substrate 230, and the dielectric tube 210 and the dielectric rod 220 are not concentric. The core 100 is the core, which is located at the center of the optical fiber. The dielectric tube 210, the dielectric rod 220 and the substrate 230 are the cladding of the optical fiber. The dielectric tube 210 and the dielectric rod 220 constitute microstructure units in the optical fiber cladding, and these microstructure units are arranged with the core as the symmetric center, and the number of microstructure units N=3. The material of the cladding area is any one of silica, soft glass or plastic.

[0049] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation to the invention.

[0050] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example.

[0051] Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Mentioning "embodiment" in this article means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present embodiment application. The appearance of this phrase in various positions in the specification is not necessarily the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It can be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0052] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. An all-solid-state large mode field single-mode optical fiber, characterized in that: include: A fiber core (100), the fiber core (100) being located at the center of the optical fiber and being a dielectric round rod; A cladding (200), the cladding (200) comprising a plurality of microstructure units and a substrate (230), the microstructure units being arranged with the fiber core (100) as the symmetric center, and the substrate (230) being filled between the fiber core (100) and the microstructure units, wherein: The microstructure unit is composed of a dielectric tube (210) and a dielectric rod (220), and the refractive index of the dielectric tube is n 3 is greater than the refractive index of the dielectric rod n 4.

2. The all-solid-state large mode field single-mode optical fiber according to claim 1, characterized in that: The core radius R0 of the optical fiber is greater than 15 μm, and the normalized parameter Much larger than 2.405, among which, n 1 is the refractive index of the fiber core (100), n 2 is the refractive index of the substrate (230), R0 is the radius of the core (100), λ is the operating wavelength.

3. The all-solid-state large mode field single-mode optical fiber according to claim 1, characterized in that: The microstructure unit is tangential to or separated from the fiber core (100); When separated, the shortest distance between the edge of the fiber core (100) and the edge of the microstructure unit should be of the order of magnitude of the operating wavelength.

4. The all-solid-state large mode field single-mode optical fiber according to claim 1, characterized in that: The cross section of the medium pipe (210) includes a circular ring shape or an elliptical ring shape.

5. The all-solid-state large mode field single-mode optical fiber according to claim 1, characterized in that: The cross section of the dielectric rod (220) may be circular or elliptical.

6. The all-solid-state large mode field single-mode optical fiber according to claim 1, characterized in that: The positional relationship between the dielectric tube (210) and the dielectric rod (220) includes concentricity or non-concentricity.

7. The all-solid-state large mode field single-mode optical fiber according to claim 1, characterized in that: The plurality of microstructure units are arranged at equal intervals with the fiber core (100) as the symmetric center; The connecting lines between the center points of the microstructure units form a regular polygon, and the fiber core is located at the center of the regular polygon.

8. The all-solid-state large mode field single-mode optical fiber according to claim 7, characterized in that: The microstructure units can be arranged in a single layer.

9. The all-solid-state large mode field single-mode optical fiber according to claim 7, characterized in that: The number of the microstructure units N=2, 3, 4, 5, 6, 7, 8.

10. The all-solid-state large mode field single-mode optical fiber according to claim 2, characterized in that: Refractive index of the dielectric tube (210) n 3 is greater than the refractive index of the substrate (230) n 2.

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