Ultra-wideband single-mode single-polarization terahertz photonic crystal fiber

Abstract

The application discloses an ultra-wideband single-mode single-polarization terahertz photonic crystal fiber, which comprises a base, a cladding and a core; the cladding and the core are arranged in the base, and the core is located at the center position of the cladding; the core comprises three core regions, a first core region is a hexagonal region composed of a plurality of first air holes; a second core region is a hexagonal region composed of a plurality of first core regions; and a third core region is composed of a plurality of second core regions; the three core regions jointly form a core region of a honeycomb type porous core. The application breaks the symmetry of the core structure through the design of the core structure, improves the working bandwidth of the fiber, and makes the single-mode single-polarization working bandwidth of the fiber reach 6.9 THz in the frequency range of 2.6 THz to 9.5 THz.

Description

Technical Field

[0001] This application relates to an ultrawide bandwidth single-mode single-polarization terahertz photonic crystal fiber, belonging to the field of optical fiber communication. Background Technology

[0002] Research has found that by altering the size, shape, or arrangement of air holes in the two polarization directions of the optical fiber, the circular symmetry of the cladding and core structures of the photonic crystal fiber can be broken, thereby achieving the goal of controlling the refractive index distribution characteristics of the fiber. Single-Polarization Single-Mode Terahertz Photonic Crystal Fiber (SPSM-THz-PCF) is a special type of fiber, particularly suitable for high-precision optical devices such as fiber optic gyroscopes, coherent optical transceivers, and micro-displacement sensors. Unlike traditional single-mode single-polarization terahertz fibers, this photonic crystal fiber exhibits a wide single-mode single-polarization operating bandwidth and low transmission loss in the terahertz range.

[0003] There are mainly three ways to achieve single-mode and single-polarization terahertz photonic crystal fibers by breaking the symmetry of the fiber structure: (1) filling the fiber core with substrate materials of different refractive indices; (2) introducing a porous core structure into the fiber core; (3) introducing defects into the cladding. Wang (Wang B K, Tian F J, Liu G Y, et al. A modified single-polarization THz fiber with epsilon-near-zero (ENZ) material [J]. Results in Optics, 2020, 1(100034): 2666 - 9501) proposed a fiber based on a square lattice structure, and chose to fill a near-zero refractive index substrate material called Epsilon-Near-Zero (ENZ) in the square lattice of the cladding, and finally obtained a single-mode and single-polarization working bandwidth of 0.347 THz. Yang (Yang T Y, Ding C, Ziolkowski R W, et al. An Epsilon-Near-Zero (ENZ) Based, Ultra-WideBandwidth Terahertz Single-Polarization Single-Mode Photonic Crystal Fiber [J]. Journal of Lightwave Technology, 2021, 39(1): 223 - 232) proposed a trench-type single-mode and single-polarization photonic crystal fiber filled with ENZ material, and obtained a single-mode and single-polarization working bandwidth of 0.64 THz. Jiang (Jiang Wenli, Zheng Yi. Design of high birefringence single-mode and single-polarization terahertz photonic crystal fibers [J]. Optical Communication Research, 2016, 1: 22 - 25) proposed a single-mode and single-polarization photonic crystal fiber with an asymmetric triangular lattice. By introducing three elliptical small holes into the core to break the fiber symmetry, a working bandwidth of 0.8 THz near 1 THz was achieved. Wang (Wang Jingli, Lu Chi. Achieving single-mode and single-polarization terahertz PCF based on structural adjustment [J]. Optical Communication Research, 2018, (04): 18 - 21) adjusted the two large air holes in the x-axis direction in the sub-inner cladding, and replaced the original two circular large air holes with two regular hexagons composed of countless small air holes, and achieved a single-mode and single-polarization working bandwidth of 0.281 THz near 0.8 THz.

[0004] It can be seen that the existing single-mode and single-polarization terahertz photonic crystal fibers have the problem that the wide single-mode and single-polarization working frequency band and low loss cannot be兼顾 simultaneously. Achieving a terahertz photonic crystal fiber with a wide single-mode and single-polarization working frequency band and low transmission loss is still a challenge in the field of practical engineering applications. It should be noted that the Chinese word "兼顾" in the original text is not accurately translated in the above English text. A more appropriate translation could be "balanced simultaneously" or "taken into account simultaneously". The translation is adjusted according to the context for better understanding.Summary of the Invention

[0005] According to one aspect of this application, an ultrawide bandwidth single-mode single-polarization terahertz photonic crystal fiber is provided, which improves the single-mode single-polarization operating bandwidth of the terahertz photonic crystal fiber through an asymmetric arrangement structure design of the fiber core.

[0006] The ultrawide bandwidth single-mode single-polarization terahertz photonic crystal fiber includes a substrate, a cladding, and a core.

[0007] The cladding and the fiber core are disposed within the substrate, with the fiber core located at the center of the cladding;

[0008] The cladding is composed of a plurality of air holes arranged in a manner;

[0009] The fiber core includes a first fiber core region, a second fiber core region, and a third fiber core region;

[0010] The first fiber core region is a hexagonal region composed of a plurality of first air holes;

[0011] The second core region is a hexagonal region composed of several first core regions;

[0012] The third fiber core region is composed of several second fiber core regions;

[0013] The first core region, the second core region, and the third core region together constitute the core region of the honeycomb porous core.

[0014] Optionally, in the first fiber core region, a plurality of the first air holes are symmetrically arranged with the center of one of the first air holes as the center position;

[0015] In the second fiber core region, a plurality of first fiber core regions are symmetrically arranged with the center of one of the first fiber core regions as the center position;

[0016] The second fiber core region is symmetrically arranged within the third fiber core region.

[0017] Optionally, each of the first fiber core regions includes seven of the first air holes;

[0018] Each second core region includes seven first core regions;

[0019] The third core region includes two of the second core regions.

[0020] Optionally, in the first fiber core region, the distance l1 between the centers of two adjacent first air holes is 7.3 μm to 7.7 μm. Preferably, l1 = 7.5 μm.

[0021] Optionally, in the second fiber core region, the distance l2 between the center positions of two adjacent first fiber core regions is 19 μm to 21 μm. Preferably, l2 = 20 μm.

[0022] Optionally, in the third fiber core region, the distance h between the center positions of two adjacent second fiber core regions is 26 μm to 34 μm. Preferably, h = 30 μm.

[0023] Optionally, the cladding is formed by a second air hole and a third air hole arranged in a circular lattice;

[0024] The cladding has several layers of air holes, counted from the inside out, with the third air hole located in the second layer;

[0025] The diameter of the third air hole is larger than the diameter of the second air hole;

[0026] Preferably, the diameter of the first air hole is smaller than the diameter of the second air hole.

[0027] Optionally, the first air hole, the second air hole, and the third air hole are all circular;

[0028] The radius r of the first air hole is 1.3 μm to 2.1 μm; preferably, r = 1.7 μm.

[0029] The radius R of the second air hole is 33μm to 37μm; preferably, R = 35μm.

[0030] The radius R1 of the third air hole is 68 μm to 72 μm. Preferably, R1 = 70 μm.

[0031] Optionally, the cladding has five layers of air holes, which are, from the inside out, a first air hole layer, a second air hole layer, a third air hole layer, a fourth air hole layer, and a fifth air hole layer.

[0032] The first air hole layer includes six second air holes;

[0033] The second air hole layer includes 10 second air holes and 2 third air holes, with the center of the cladding layer as the coordinate far point, and the third air holes are located in the y-axis direction;

[0034] The third air hole layer includes 18 second air holes;

[0035] The fourth air hole layer includes 24 of the second air holes;

[0036] The fifth air-hole layer includes 30 second air holes;

[0037] Preferably, the distance Λ between the centers of two adjacent second air holes is 100 μm to 104 μm. Preferably, Λ = 102 μm.

[0038] Optionally, the substrate is made of a cyclic olefin copolymer (COC).

[0039] The beneficial effects that this application can produce include:

[0040] 1) The ultra-wideband single-mode single-polarization terahertz photonic crystal fiber provided in this application designs the fiber core as a first fiber core region, a second fiber core region and a third fiber core region. The three regions together form a honeycomb-type porous fiber core region. Due to the asymmetrical arrangement of the porous core structure, the symmetry of the fiber core structure is broken, thereby improving the single-mode single-polarization working bandwidth of the terahertz photonic crystal fiber.

[0041] 2) The ultra-wideband single-mode single-polarization terahertz photonic crystal fiber provided in this application has a cladding arranged in a typical circular lattice. By introducing a third air hole with a different size from the second air hole in the cladding structure, i.e. introducing a defect in the fiber core, the symmetry of the fiber cross section is broken. Combined with the asymmetrically arranged fiber core structure, the single-mode single-polarization working bandwidth of the terahertz fiber is further improved.

[0042] 3) The ultra-wideband single-mode single-polarization terahertz photonic crystal fiber provided in this application has a single-mode single-polarization working bandwidth of up to 6.9THz in the frequency range of 2.6THz to 9.5THz. Attached Figure Description

[0043] Figure 1 A schematic diagram of the cross-sectional structure of the ultrawide bandwidth single-mode single-polarization terahertz photonic crystal fiber provided in this application;

[0044] Figure 2 This is a diagram of the single-mode, single-polarization operating bandwidth of the optical fiber provided in Embodiment 1 of this application;

[0045] Figure 3 A pseudo-color image showing the bending loss of the optical fiber as a function of frequency and bending radius, provided in Embodiment 1 of this application.

[0046] Figure 4 The mode field distribution diagram of the optical fiber provided in Embodiment 1 of this application at 2.6 THz in the y-polarization state is shown.

[0047] Figure 5 The mode field distribution diagram of the optical fiber provided in Embodiment 1 of this application at 2.6 THz in the x-polarization state is shown.

[0048] Figure 6 This is a mode field distribution diagram of the optical fiber in the y-polarization state at 5THz provided in Embodiment 1 of this application;

[0049] Figure 7 This is a mode field distribution diagram of the optical fiber in the x-polarization state at 5 THz provided in Embodiment 1 of this application;

[0050] List of components and reference numerals:

[0051] 1-Substrate; 2-Clad layer; 3-Core; 4-First core region; 5-Second core region; 6-Third core region; 7-First air hole; 8-Second air hole; 9-Third air hole. Detailed Implementation

[0052] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0053] This application provides an ultrawideband single-mode single-polarization terahertz photonic crystal fiber, the cross-sectional structure of which is as follows: Figure 1 As shown, it includes a substrate 1, a cladding 2, and a fiber core 3;

[0054] The cladding 2 and the fiber core 3 are disposed within the substrate 1, and the fiber core 3 is located at the center of the cladding 2;

[0055] The fiber core 3 includes a first fiber core region 4, a second fiber core region 5, and a third fiber core region 6.

[0056] The first fiber core region 4 is a hexagonal region composed of a plurality of first air holes 7; the first fiber core region 4 is the basic unit constituting the fiber core region, and the second fiber core region 5 and the third fiber core region 6 are both formed by arranging a plurality of first fiber core regions 4. Those skilled in the art can select the number and arrangement of the first air holes constituting the hexagonal region of the first fiber core region according to the requirements and feasibility. In the implementation of this application, the first fiber core region 4 is designed with 7 first air holes, one of which is located at the center of the first fiber core region, and the other six first air holes are symmetrically arranged with the center of the first fiber core region as the center position, that is, the six first air holes are respectively located at the six vertices of the regular hexagon.

[0057] The second fiber core region 5 is a hexagonal region composed of several first fiber core regions 4. Those skilled in the art can select the number and arrangement of the first fiber core regions constituting the hexagonal region of the second fiber core region according to the requirements and feasibility. In the implementation of this application, seven first fiber core regions are designed in the second fiber core region. The arrangement of the seven first fiber core regions in the second fiber core region is the same as the arrangement of the first air holes in the first fiber core region. That is, the six first fiber core regions are symmetrically arranged with the center of one of the first fiber core regions as the center position.

[0058] The third fiber core region 6 is composed of several second fiber core regions 5. The third fiber core region 6 is a pseudo-hexagonal region, that is, the outer contour of the region is not completely formed by the outer contour of the multiple second fiber core regions 5 arranged together, but rather by the outer contour of the only second fiber core regions 5 within the region, which can form a partial contour of the hexagonal region's outer contour. For example, in the implementation of this application, the third fiber core region includes two second fiber core regions, and the centers of the two second fiber core regions and the third fiber core region are symmetrically arranged at the center position. The two adjacent edge contours of each second fiber core region are both part of the two edge contours of the third fiber core region. Furthermore, the apex of the second fiber core region is located at the apex of the third fiber core region.

[0059] Since the triangular lattice in the fiber core has a greater impact on the optical waveguide mode characteristics than the circular lattice in the cladding, introducing anisotropic microstructure air holes in the fiber core region makes it easier to obtain a wider single-mode single-polarization operating bandwidth and a larger mode field area, among other excellent characteristics. Therefore, through the design of the above structure, this application enables the first, second, and third fiber core regions to jointly form the core region of a honeycomb porous fiber core, thereby creating an asymmetrical arrangement of porous structures in the core, breaking the symmetry of the core structure, and thus improving the single-mode single-polarization operating bandwidth of the terahertz fiber.

[0060] In a further specific implementation, in the first fiber core region 4, the distance l1 between the centers of two adjacent first air holes is 7.3 μm to 7.7 μm. In the second fiber core region 5, the distance l2 between the centers of two adjacent first fiber core regions 4 is 19 μm to 21 μm. In the third fiber core region 6, the distance h between the centers of two adjacent second fiber core regions 5 is 26 μm to 34 μm.

[0061] The cladding layer 2 is composed of a plurality of air holes arranged in a manner;

[0062] Specifically, the cladding 2 is formed by the second air hole 8 and the third air hole 9 arranged in a circular lattice; that is, the second air hole 8 and the third air hole 9 in the cladding 2 are arranged around the center of the fiber core 3 as a circle, and around circles of different radii.

[0063] The cladding 2 has several layers of air holes, counted from the inside out, with the third air hole 9 located in the second layer;

[0064] The diameter of the third air hole 9 is larger than the diameter of the second air hole 2;

[0065] The diameter of the first air hole 7 is smaller than the diameter of the second air hole 8.

[0066] In the implementation of this application, the air holes in the cladding 2 are designed to be 5 layers, namely the first air hole layer, the second air hole layer, the third air hole layer, the fourth air hole layer and the fifth air hole layer from the inside out;

[0067] The first air hole layer includes six second air holes;

[0068] The second air hole layer includes 10 second air holes and 2 third air holes, with the center of the cladding layer 2 as the origin of the coordinate system, and the third air hole 9 is located in the y-axis direction;

[0069] The third air hole layer includes 18 second air holes;

[0070] The fourth air hole layer includes 24 of the second air holes;

[0071] The fifth air pore layer includes 30 second air pores.

[0072] In a further specific implementation process, the first air hole 7, the second air hole 8, and the third air hole 9 are all circular;

[0073] The radius r of the first air hole 7 is 1.3 μm to 2.1 μm; preferably, r = 1.7 μm.

[0074] The radius R of the second air hole 8 is 33μm to 37μm; preferably, R = 35μm.

[0075] The radius R1 of the third air hole 9 is 68μm to 72μm. Preferably, R1 = 70μm.

[0076] The distance Λ between the centers of two adjacent second air holes is 100μm to 104μm.

[0077] For the substrate 1, those skilled in the art can select it according to actual needs. In this application, a cyclic olefin copolymer (COC) is used as the substrate material. The cyclic olefin copolymer (COC) is an amorphous polymer with a relatively stable refractive index of 1.52 in the range of 2.6–9.5 THz and a low bulk absorption coefficient.

[0078] Example 1

[0079] The ultrawide bandwidth single-mode single-polarization terahertz photonic crystal fiber includes a substrate 1, a cladding 2 and a core 3. The cladding 2 and the core 3 are disposed within the substrate 1, and the core 3 is located at the center of the cladding 2.

[0080] Substrate 1 is a cyclic olefin copolymer (COC);

[0081] The fiber core 3 includes a first fiber core region 4, a second fiber core region 5, and a third fiber core region 6. The three regions together form the fiber core regions of the honeycomb porous fiber core.

[0082] The first fiber core region 4 contains 7 circular first air holes 7. One first air hole 7 is located at the center of the first fiber core region 4, and the other six first air holes 7 are symmetrically arranged with the center of the first fiber core region 4 as the center, forming a regular hexagonal region. The radius of the first air hole 7 is r = 1.7 μm, and the distance between the centers of two adjacent first air holes 7 is l1 = 7.5 μm.

[0083] The first fiber core region 5 contains seven first fiber core regions 4, and the arrangement of the seven first fiber core regions 4 is the same as the arrangement of the first air holes in the first fiber core region 4; the distance between the centers of two adjacent first fiber core regions 4 is l2 = 20 μm.

[0084] The third core region 6 contains two first core regions 5, which are symmetrically arranged with the center of the third core region 6 as the center; the distance between the centers of the two second core regions 5 is h = 30 μm.

[0085] The cladding 2 is composed of circular second air holes 8 and third air holes 9 arranged in a circular lattice. Counting from the inside out, the first layer consists of 6 second air holes 8, the second layer consists of 2 third air holes 9 along the y-axis and the remaining 10 second air holes 8, and the third, fourth and fifth layers consist of 18, 24 and 30 second air holes 8, respectively. The radius of the second air hole 8 is R = 35 μm; the radius of the third air hole 9 is R1 = 70 μm; and the distance between the centers of two adjacent second air holes 8 is Λ = 102 μm.

[0086] The operating bandwidth of the optical fiber provided in Example 1 was simulated and tested. The test results are as follows: Figure 2 As shown, the optical fiber of this application has a single-mode single-polarization operating bandwidth of up to 6.9THz in the frequency range of 2.6THz to 9.5THz.

[0087] Simulation tests were conducted to examine the bending loss of the optical fiber provided in Example 1 as a function of frequency and bending radius. The test results are as follows: Figure 3 As shown in the figure, when the incident light frequency remains constant (fixed y-axis value), as the bending radius increases, the color of the bending loss value changes from red to blue, indicating a decrease in bending loss. When the bending radius remains constant (fixed x-axis value), as the frequency increases, the bending loss value changes from high to low, indicating a decrease in bending loss.

[0088] Simulation tests were performed on the mode field distribution of the optical fiber provided in Example 1 under different polarization states and frequencies. The test results are as follows: Figure 4-7 As shown, where Figure 4 , Figure 6 This is the mode field distribution diagram of the optical fiber y-polarization state at 2.6THz and 5THz provided in Example 1; Figure 5 , Figure 7 This is the mode field distribution diagram of the x-polarization state of the optical fiber provided in Example 1 at 2.6THz and 5THz. Figure 4 It can be seen that the y-polarized mode is well confined within the fiber core and propagates at the single-mode single-polarization initiation frequency of 2.6 THz, with almost no leakage; while from Figure 5 It can be seen that a portion of the mode field energy of the x-polarized mode at the single-mode single-polarization initiation frequency has already entered the cladding of the optical fiber; Figure 6 This is the mode field energy distribution diagram of the y-polarized mode at 5 THz after increasing the incident light frequency, for comparison. Figure 4 It can be seen that as the incident light frequency increases, the y-direction polarization mode is better confined in the fiber core, and the mode field becomes more concentrated. Conversely, Figure 7 The mode field of the x-polarized mode at 5 THz has completely leaked into the cladding, meaning that the fiber has achieved single-mode single-polarization transmission at 5 THz.

[0089] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. An ultra-wide bandwidth single-mode single-polarization terahertz photonic crystal fiber, characterized in that, The photonic crystal fiber includes a substrate, a cladding, and a core. The cladding and the fiber core are disposed within the substrate, with the fiber core located at the center of the cladding; The cladding is composed of a plurality of air holes arranged in a manner; The fiber core includes a first fiber core region, a second fiber core region, and a third fiber core region; The first fiber core region is a hexagonal region composed of a plurality of first air holes; The second core region is a hexagonal region composed of several first core regions; The third fiber core region is composed of several second fiber core regions; The first core region, the second core region, and the third core region together constitute the core region of the honeycomb porous fiber core; The cladding is formed by a second air hole and a third air hole arranged in a circular lattice; The first air hole, the second air hole, and the third air hole are all circular; The radius r of the first air hole is 1.3 μm to 2.1 μm; The radius R of the second air hole is 33μm~37μm; The radius R1 of the third air hole is 68μm~72μm.

2. The ultra-widebandwidth single-mode single-polarization terahertz photonic crystal fiber according to claim 1, characterized in that, In the first fiber core region, a plurality of first air holes are symmetrically arranged with the center of one of the first air holes as the center position; In the second fiber core region, a plurality of first fiber core regions are symmetrically arranged with the center of one of the first fiber core regions as the center position; The second fiber core region is symmetrically arranged within the third fiber core region.

3. The ultra-widebandwidth single-mode single-polarization terahertz photonic crystal fiber according to claim 2, characterized in that, Each of the first fiber core regions includes 7 of the first air holes; Each second core region includes seven first core regions; The third core region includes two of the second core regions.

4. The ultra-widebandwidth single-mode single-polarization terahertz photonic crystal fiber according to claim 1, characterized in that, In the first fiber core region, the distance l1 between the centers of two adjacent first air holes is 7.3 μm to 7.7 μm.

5. The ultra-widebandwidth single-mode single-polarization terahertz photonic crystal fiber according to claim 1, characterized in that, In the second fiber core region, the distance l2 between the center positions of two adjacent first fiber core regions is 19μm~21μm.

6. The ultra-widebandwidth single-mode single-polarization terahertz photonic crystal fiber according to claim 1, characterized in that, In the third fiber core region, the distance h between the center positions of two adjacent second fiber core regions is 26μm~34μm.

7. The ultra-widebandwidth single-mode single-polarization terahertz photonic crystal fiber according to claim 1, characterized in that, The cladding has several layers of air holes, counted from the inside out, with the third air hole located in the second layer; The diameter of the third air hole is larger than the diameter of the second air hole; Preferably, the diameter of the first air hole is smaller than the diameter of the second air hole.

8. The ultra-widebandwidth single-mode single-polarization terahertz photonic crystal fiber according to claim 7, characterized in that, The cladding has five layers of air holes, which are, from the inside out, the first air hole layer, the second air hole layer, the third air hole layer, the fourth air hole layer and the fifth air hole layer; The first air hole layer includes six second air holes; The second air hole layer includes 10 second air holes and 2 third air holes, with the center of the cladding layer as the coordinate far point, and the third air holes are located in the y-axis direction; The third air hole layer includes 18 second air holes; The fourth air hole layer includes 24 of the second air holes; The fifth air-hole layer includes 30 second air holes; Preferably, the distance between the centers of two adjacent second air holes The range is 100μm to 104μm.

9. The ultra-widebandwidth single-mode single-polarization terahertz photonic crystal fiber according to any one of claims 1-7, characterized in that, The substrate is made of cyclic olefin copolymer (COC).

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