A photonic crystal fiber that is resistant to bending and has a high Brillouin scattering gain

Abstract

The application discloses a kind of photonic crystal fiber of bending resistance and with high Brillouin scattering gain, including surface layer, intermediate layer and core layer;Surface layer includes first oval air hole, and first oval air hole is arranged along the circumferential direction of photonic crystal fiber;Intermediate layer includes first part, second part, third part and fourth part, first part and third part are oppositely arranged, and respectively include a plurality of first circular air hole arranged into trapezoidal;Second part and fourth part are oppositely arranged, and respectively include a plurality of first circular air hole arranged into square;Core layer includes two symmetrically arranged second circular air hole, and the gap between each second circular air hole and first part and third part is filled with symmetrically arranged third circular air hole and third oval air hole.The application not only has good bending resistance, but also has higher Brillouin scattering gain.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber communication technology, specifically relating to a photonic crystal fiber that is resistant to bending and has high Brillouin scattering gain. Background Technology

[0002] Photonic crystal fiber is a type of optical fiber with a unique structure and properties. Its bending resistance and Brillouin scattering gain characteristics play a crucial role in applications such as optical communication, sensing, and lasers. The unique feature of this fiber is that, by adjusting its structural parameters, such as pore arrangement, pore size, and material selection, the desired bending resistance and high Brillouin scattering gain can be achieved.

[0003] Traditional optical fibers suffer significant losses during long-distance transmission, resulting in substantial signal strength loss over extended distances. This loss is exacerbated by unavoidable external forces such as stretching and bending. Therefore, the bend resistance of photonic crystal fibers is crucial for stable long-distance optical transmission systems.

[0004] In fields such as industry, medicine, and environmental monitoring, researchers can leverage the unique characteristics of Brillouin scattering gain to monitor physical quantities such as temperature, strain, and pressure. However, for high-speed optical communication systems, the Brillouin scattering gain coefficient of traditional solid-core optical fibers is typically low, which limits the signal-to-noise ratio and measurement accuracy in sensing systems. To address this challenge, the high Brillouin scattering gain characteristics of photonic crystal fibers are particularly important.

[0005] In summary, photonic crystal fibers have broad application prospects in optical communication, sensing, and lasers. Their excellent bending resistance and high Brillouin scattering gain characteristics provide crucial technical support for various application scenarios. In 2019, Lu Yuangang et al. proposed a high Brillouin photonic crystal fiber with a Brillouin gain coefficient of 5.83*10. -12 W / m, and the birefringence coefficient is only 1.6*10. -3 All of these aspects need improvement. Summary of the Invention

[0006] To address the aforementioned problems, this invention proposes a photonic crystal fiber that is both bend-resistant and has high Brillouin scattering gain, exhibiting not only excellent bend resistance but also high Brillouin scattering gain.

[0007] To achieve the above-mentioned technical objectives and effects, the present invention is implemented through the following technical solution:

[0008] A photonic crystal fiber that is bend-resistant and has high Brillouin scattering gain includes a core and a cladding, wherein the cladding includes a top layer, an intermediate layer and a core layer arranged sequentially.

[0009] The surface layer includes several sets of axisymmetrically arranged first elliptical air holes, all of which are arranged along the circumferential direction of the photonic crystal fiber.

[0010] The intermediate layer includes a first part, a second part, a third part, and a fourth part arranged along the circumference of the photonic crystal fiber. The first part and the third part are arranged opposite to each other, and each of them includes a plurality of first circular air holes arranged in a trapezoidal shape. The second part and the fourth part are arranged opposite to each other, and each of them includes a plurality of first circular air holes arranged in a square shape.

[0011] The core layer includes two symmetrically arranged second circular air holes, and the gaps between each second circular air hole and the first and third parts are filled with symmetrically arranged third circular air holes and third elliptical air holes.

[0012] Optionally, the diameter of the second circular air hole is larger than the diameter of the first circular air hole, and the diameter of the first circular air hole is larger than the diameter of the third circular air hole.

[0013] Optionally, the diameter of the first circular air hole is d1 = 0.8-0.9 μm; the diameter of the second circular air hole is d2 = 1.2-1.25 μm; and the diameter of the third circular air hole is d3 = 0.7-0.75 μm.

[0014] Optionally, the spacing between adjacent first circular air holes is k1 = 0.82 µm; the spacing between adjacent second circular air holes is k2 = 2.7 µm in the longitudinal direction; and the spacing between adjacent third circular air holes is k3 = 1.6 µm in the longitudinal direction.

[0015] Optionally, the major axis of the first elliptical air hole is a2 = 3.0-3.1 µm, and the minor axis is b2 = 0.7-0.75 µm.

[0016] Optionally, the photonic crystal fiber further includes a pair of second elliptical air holes, the second elliptical air holes and all the first elliptical air holes being arranged along the circumference of the photonic crystal fiber, and the central axis of the second elliptical air holes coinciding with that of the second circular air holes, the major axis of the second elliptical air holes being a1=1.5-1.6 µm, and the minor axis being b1=0.6-0.65 µm.

[0017] Optionally, the major axis of the third elliptical air hole is a3 = 0.82-0.9µm, and the minor axis is b3 = 0.4-0.45µm.

[0018] Optionally, the spacing between adjacent third elliptical air holes is k4 = 1.8 µm in the horizontal axis direction and k5 = 3.2 µm in the vertical axis direction.

[0019] Optionally, the photonic crystal fiber has a gain factor of 1.03*10 at the acoustic field characteristic frequency of 2533.7 MHz. -11 W / m.

[0020] Optionally, the photonic crystal fiber has an effective refractive index of 1.3515 in the x-polarization direction, an effective refractive index of 1.341 in the y-polarization direction, and a birefringence of 1.05 × 10⁻⁶. -2 .

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] This invention discloses a bend-resistant photonic crystal fiber with high Brillouin scattering gain. Utilizing a multi-cladding structure, it better confines optical energy within the fiber core, resulting in excellent bend resistance. Furthermore, the outermost cladding employs elliptical air holes, which reduce the effective diameter of the fiber core, thereby decreasing the mode field area, enhancing acousto-optic coupling efficiency, and increasing the intensity of the Brillouin scattering gain spectrum. Compared to traditional step-index fibers, the Brillouin scattering gain coefficient is increased by approximately 6 times. Therefore, it meets the requirements of long-distance transmission optical systems and fiber optic sensing. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0024] Figure 1(a) is one of the structural schematic diagrams of a photonic crystal fiber in one embodiment of the present invention;

[0025] Figure 1(b) is a second schematic diagram of the structure of a photonic crystal fiber in one embodiment of the present invention;

[0026] Figure 2 This is a distribution diagram of the mode field in the x-polarization direction of a photonic crystal fiber and its refractive index in the x-polarization direction, according to one embodiment of the present invention.

[0027] Figure 3 This is a distribution diagram of the mode field in the y-polarization direction of a photonic crystal fiber and its refractive index in the y-polarization direction, according to one embodiment of the present invention.

[0028] Figure 4This is a sound field mode distribution diagram of a photonic crystal fiber in one embodiment of the present invention, with the inset on the right representing its intensity.

[0029] Figure 5 This is a Brillouin scattering gain spectrum curve of a photonic crystal fiber in one embodiment of the present invention;

[0030] Figure 6 This is a schematic diagram of a photonic crystal fiber bending in one embodiment of the present invention;

[0031] Figure 7 This is a mode field diagram of a photonic crystal fiber in one embodiment of the present invention when it reaches the bending critical value;

[0032] Figure 8 This is a bending loss curve of a photonic crystal fiber in one embodiment of the present invention;

[0033] Figure label:

[0034] 1. Substrate material; 2. Second elliptical air hole; 3. First elliptical air hole; 4. First circular air hole; 5. Second circular air hole; 6. Third circular air hole; 7. Third elliptical air hole. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may include different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0037] In the description of this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0038] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0039] The application principle of the present invention will be described in detail below with reference to the accompanying drawings.

[0040] As shown in Figure 1, the present invention provides a photonic crystal fiber that is resistant to bending and has high Brillouin scattering gain, comprising a core and a cladding, wherein the cladding comprises a surface layer, an intermediate layer and a core layer sequentially disposed on a substrate material 1.

[0041] The surface layer includes several sets of first elliptical air holes 3 arranged symmetrically, and all the first elliptical air holes 3 are arranged along the circumferential direction of the photonic crystal fiber.

[0042] The intermediate layer includes a first part, a second part, a third part, and a fourth part arranged along the circumference of the photonic crystal fiber. The first part and the third part are arranged opposite to each other, and each of them includes a plurality of first circular air holes 4 arranged in a trapezoidal shape. The second part and the fourth part are arranged opposite to each other, and each of them includes a plurality of first circular air holes 4 arranged in a square shape.

[0043] The core layer includes two symmetrically arranged second circular air holes 5, and the gaps between each second circular air hole 5 and the first and third parts are filled with symmetrically arranged third circular air holes 6 and third elliptical air holes 7.

[0044] In one specific embodiment of the present invention, the diameter of the second circular air hole 5 is larger than the diameter of the first circular air hole 4, and the diameter of the first circular air hole 4 is larger than the diameter of the third circular air hole 6. Specifically, the diameter of the first circular air hole 4 is d1 = 0.8-0.9 μm; the diameter of the second circular air hole 5 is d2 = 1.2-1.25 μm; and the diameter of the third circular air hole 6 is d3 = 0.7-0.75 μm. The spacing between adjacent first circular air holes 4 is k1 = 0.82 μm; the spacing between adjacent second circular air holes 5 in the longitudinal direction is k2 = 2.7 μm; and the spacing between adjacent third circular air holes 6 in the longitudinal direction is k3 = 1.6 μm.

[0045] In one specific embodiment of the present invention, the major axis of the first elliptical air hole 3 is a2 = 3.0-3.1 µm, and the minor axis is b2 = 0.7-0.75 µm. The photonic crystal fiber also includes a pair of second elliptical air holes 2. The second elliptical air holes 2, together with all the first elliptical air holes 3, are arranged along the circumference of the photonic crystal fiber, and the central axis of the second elliptical air holes coincides with that of the second circular air holes. The major axis of the second elliptical air holes 2 is a1 = 1.5-1.6 µm, and the minor axis is b1 = 0.6-0.65 µm. That is, the cladding is symmetrically distributed along an octagonal axis, and the surface layer consists of eight elliptical air holes arranged in an octagonal structure, with two identical and smaller second elliptical air holes 2 directly above and below. The major axis of the third elliptical air hole 7 is a3 = 0.82-0.9 µm, and the minor axis is b3 = 0.4-0.45 µm. In the horizontal axis direction, the hole spacing between adjacent third elliptical air holes 7 is k4=1.8 µm, and in the vertical axis direction, the hole spacing between adjacent third elliptical air holes 7 is k5=3.2 µm.

[0046] Based on the above design, the photonic crystal fiber has a gain factor of 1.03*10 at the acoustic field characteristic frequency of 2533.7 MHz. -11 W / m. The effective refractive index of the photonic crystal fiber is 1.3515 in the x-polarization direction and 1.341 in the y-polarization direction, with a birefringence of 1.05*10. -2 .

[0047] The photonic crystal fiber of the present invention will be described in detail below with reference to a specific embodiment.

[0048] As shown in Figures 1(a) and 1(b), this is a photonic crystal fiber in a specific embodiment of the present invention. In this embodiment, the photonic crystal fiber has a cross-sectional diameter of D = 12 µm and includes a core and a cladding. The substrate material 1 of both the core and the cladding is silicon dioxide. The cladding is symmetrically distributed along an octagonal axis. The surface layer consists of eight elliptical air holes arranged in an octagonal structure. Two identical and smaller second elliptical air holes 2 are located directly above and below, with a major axis of a1 = 1.6 µm and a minor axis of b1 = 0.6 µm. The remaining six are first elliptical air holes 3 of the same size, with a major axis of a2 = 3 µm and a minor semi-axis of b2 = 0.7 µm. The intermediate layer consists of first circular air holes 4 of the same size, which can be divided into four parts: top, bottom, left, and right. The diameter of the first circular air hole 4 is d1 = 0.8 µm. The first circular air holes 4 on both the left and right sides are arranged in a trapezoidal shape, forming a trapezoidal grid consisting of 6 first circular air holes 4 with a hole spacing of k1=0.82 µm at the top base and 10 first circular air holes 4 with a hole spacing of k1=0.82 µm at the bottom base, and the two parts are symmetrical about the vertical axis; the first circular air holes 4 in the upper and lower parts are arranged in a square shape, and are symmetrical about the horizontal axis. The core layer consists of a second circular air hole 5, a third circular air hole 6, and a third elliptical air hole 7. The second circular air hole 5 is located on the vertical axis, with a diameter of d2 = 1.2 µm and a spacing of k2 = 2.7 µm. A pair of third circular air holes 6 and third elliptical air holes 7 are placed vertically and symmetrically distributed on both sides of the second circular air hole 5. The spacing between adjacent third circular air holes 6 is k3 = 1.6 µm, and the diameter of the third circular air hole 6 is d3 = 0.7 µm. The four third elliptical air holes 7 are on a rectangular grid, with a spacing of k4 = 1.8 µm in the horizontal direction and k5 = 3.2 µm in the vertical direction. The major axis of the third elliptical air hole 7 is a3 = 0.82 µm, and the minor axis is b3 = 0.4 µm.

[0049] like Figure 2 , 3 As shown in Figures 4 and 5, the main peak of the Brillouin scattering gain spectrum of the photonic crystal fiber exhibits a Lorentz spectral distribution. The main peak is primarily obtained by the coupling between the acoustic fundamental mode and the optical fundamental mode, and it shows a maximum gain at the characteristic frequency of 2533.7 MHz, with a gain coefficient of 1.03 × 10⁻⁶. -11 W / m. The Brillouin scattering gain of a traditional step-index fiber is 1.6*10. -12W / m, the Brillouin scattering gain of this invention is more than 6 times that. The mode field distribution diagrams of the photonic crystal fiber in the x-polarization and y-polarization directions of this invention are shown. The effective refractive index of the fiber in the x-polarization direction is 1.3515, the effective refractive index in the y-polarization direction is 1.341, and the birefringence is 1.05*10. -2 Compared to existing photonic crystal fibers (which typically have a birefringence of 10), -4 This represents an increase of 1-2 orders of magnitude.

[0050] like Figure 6 , 7 As shown in Figure 8, when the optical fiber is not bent, the incident light energy is well concentrated in the fiber core during propagation. When the optical fiber is bent and the bending radius is small, the fundamental mode spot deforms and shrinks towards one side of the fiber core, but the light energy is still well concentrated in the fiber core, and there is no leakage into the cladding region. Therefore, the use of multiple air holes in the cladding region effectively improves the bending performance of the optical fiber, ensuring that even when the bending radius is as small as millimeters, there is no large-scale energy leakage into the cladding. At a bending radius of 1 mm, the bending loss reaches 1.96 × 10⁻⁶ mm. -5 dB / km.

[0051] This invention calculates the gain coefficient corresponding to the characteristic frequency based on the Brillouin scattering gain calculation formula, and simulates the fiber bending situation in the two-dimensional axisymmetric mode in the finite element analysis software Comsol, and calculates the fiber bending loss according to the bending loss calculation formula.

[0052] This invention achieves symmetry changes by altering the shape, size, or arrangement of air holes near the fiber core, thereby obtaining different optical properties.

[0053] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only used to facilitate the description of the present invention and to simplify the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the scope of protection of the present invention.

[0054] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A photonic crystal fiber which is resistant to bending and has a high Brillouin scattering gain, comprising a core and a cladding, characterized by, The cladding comprises a surface layer, an intermediate layer and a core layer arranged in sequence; The surface layer comprises a plurality of groups of first elliptical air holes arranged in axial symmetry, all the first elliptical air holes being arranged along the circumferential direction of the photonic crystal fiber; The intermediate layer comprises a first portion, a second portion, a third portion and a fourth portion arranged along the circumferential direction of the photonic crystal fiber, the first portion and the third portion being oppositely arranged and each comprising a plurality of first circular air holes arranged in a trapezoidal shape; the second portion and the fourth portion being oppositely arranged and each comprising a plurality of first circular air holes arranged in a square shape; The core layer comprises two symmetrically arranged second circular air holes, each second circular air hole being filled with a symmetrically arranged third circular air hole and a third elliptical air hole in the gap between the first portion and the third portion; The diameter of the second circular air hole is greater than the diameter of the first circular air hole, and the diameter of the first circular air hole is greater than the diameter of the third circular air hole; The diameter of the first circular air hole is d1=0.8-0.9µm; the diameter of the second circular air hole is d2=1.2-1.25µm; and the diameter of the third circular air hole is d3=0.7-0.75µm; The inter-hole spacing of adjacent first circular air holes is k1=0.82µm; In the longitudinal axis direction, the inter-hole spacing of adjacent second circular air holes is k2=2.7µm; In the longitudinal axis direction, the inter-hole spacing of adjacent third circular air holes is k3=1.6µm; The major axis of the first elliptical air hole is a2=3.0-3.1µm, and the minor axis is b2=0.7-0.75µm; The photonic crystal fiber further comprises a pair of second elliptical air holes, the second elliptical air holes being arranged along the circumferential direction of the photonic crystal fiber together with all the first elliptical air holes, and the major axis of the second elliptical air hole coincides with the central axis of the second circular air hole, the major axis of the second elliptical air hole being a1=1.5-1.6µm, and the minor axis being b1=0.6-0.65µm; The major axis of the third elliptical air hole is a3=0.82-0.9µm, and the minor axis is b3=0.4-0.45µm; In the transverse axis direction, the inter-hole spacing of adjacent third elliptical air holes is k4=1.8µm, and in the longitudinal axis direction, the inter-hole spacing of adjacent third elliptical air holes is k5=3.2µm.

2. The photonic crystal fiber according to claim 1, wherein: The photonic crystal fiber has a gain coefficient of 1.03*10 -11 W / m at the acoustic field characteristic frequency of 2533.7 MHz.

3. The bend-resistant photonic crystal fiber with high Brillouin scattering gain according to claim 1, characterized in that: The effective refractive index of the photonic crystal fiber in the x polarization direction is 1.3515, the effective refractive index in the y polarization direction is 1.341, and the birefringence coefficient is 1.05*10 -2 .

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