A new type of high birefringence photonic crystal fiber

Abstract

The present invention discloses a novel high-birefringence photonic crystal fiber, belonging to the field of photonic crystal fiber communication. The optical fiber of the present invention comprises a cladding and a core, and the base material is silica, characterized in that: the left and right sides of the core of the photonic crystal fiber are respectively provided with 5 layers of air holes, the innermost layer of the cladding air holes is composed of elliptical air holes arranged in a hexagonal pattern, and the long axis of the elliptical air holes is perpendicular to the x-axis, the second layer is composed of circular air holes arranged in a hexagonal pattern, the part of the second layer of air holes located on the left side of the y-axis is sequentially translated to the left by the same distance to obtain the 3rd-5th layer of air holes on the left side of the y-axis of the cladding, and the part of the second layer of air holes located on the right side of the y-axis is sequentially translated to the right by the same distance to obtain the 3rd-5th layer of air holes on the right side of the y-axis of the cladding, and the overall structure is axially symmetrically distributed. The novel high-birefringence photonic crystal fiber of the present invention can reduce the coupling in the two polarization directions during signal transmission, improve the transmission distance of the optical signal, and is suitable for the fields of long-distance optical fiber communication and optical fiber sensing.

Description

Technical Field

[0001] The invention relates to the technical field of optical fibers, and in particular to a novel high-birefringence photonic crystal optical fiber. Background Art

[0002] Photonic crystal fiber is a new type of microstructured optical fiber evolved from photonic crystal and optical fiber technology. It consists of a core and periodically arranged air holes around it. Due to the flexible parameter adjustability of photonic crystal fiber in structure, compared with traditional optical fiber, it has the characteristics of non-stop single-mode transmission, high birefringence, low loss and dispersion management. It has a wide range of applications in optical fiber sensing, optical communication, medical equipment and other fields. Distributed optical fiber sensing technology can be used as a means of fault diagnosis and accident warning in many fields such as energy, electricity, construction, communication, and transportation. Optical fiber sensing systems generally use polarization-maintaining optical fibers with high birefringence as sensing fibers to reduce the impact of polarization mode coupling in optical fibers on the signal-to-noise ratio of the sensing system. Zero-dispersion optical fibers also have unique advantages in long-distance and large-capacity optical signal transmission. Therefore, it is very necessary to design a new type of photonic crystal fiber with high birefringence.

[0003] Although existing photonic crystal fibers can achieve some of these characteristics, they cannot simultaneously achieve better birefringence and dispersion. Saha R. (Saha R, Hossain MM, Rahaman ME, et al. Frontiers of Optoelectronics, 2019, 12(2): 165-173) et al. designed a photonic crystal fiber with high birefringence at 1550 nm, with a birefringence index of 2.75×10 -2 , but its dispersion is large and needs to be optimized. Liao Kun et al. (Liao Kun, Liao Jianfei, Li Boxun, Wang Bin, Xu Biao, Xie Yingmao. A defective photonic crystal fiber with high birefringence and double zero dispersion [J]. Journal of Quantum Electronics, 2019, 36(01): 123-128) designed a photonic crystal fiber with symmetrical elliptical air hole defects. It has two zero dispersion points in the visible light band and infrared light band, and the birefringence value is only 3.327×10 -2 It can be seen that the design of new optical fibers with high birefringence and multiple zero-dispersion wavelengths is very necessary. Summary of the invention

[0004] The purpose of the present invention is to provide a photonic crystal fiber with high birefringence and multiple zero dispersion wavelengths to solve the problems existing in the photonic crystal fiber in the prior art.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A photonic crystal fiber with high birefringence and multiple zero dispersion wavelengths, wherein the cross section of the fiber includes a cladding and a core. The characteristic is that: the left and right sides of the core of the photonic crystal fiber are respectively provided with 5 layers of air holes, the innermost layer of the cladding air holes is composed of elliptical air holes arranged in a hexagonal pattern, and the long axis of the elliptical air holes is perpendicular to the x-axis, the second layer is composed of circular air holes arranged in a hexagonal pattern, the part of the second layer of air holes located on the left side of the y-axis is sequentially translated to the left by the same distance to obtain the 3rd to 5th layers of air holes on the left side of the y-axis of the cladding, and the part of the second layer of air holes located on the right side of the y-axis is sequentially translated to the right by the same distance to obtain the 3rd to 5th layers of air holes on the right side of the y-axis of the cladding, and the overall structure is axially symmetrically distributed.

[0007] Furthermore, the base material of the optical fiber is silicon dioxide.

[0008] The present invention designs a novel high birefringence photonic crystal fiber. Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0009] A high birefringence was achieved, with a 4.477×10 -2 The high birefringence coefficient is 1-2 orders of magnitude higher than that of existing optical fibers, which is beneficial to accurate measurements in optical fiber sensing.

[0010] Multiple zero-dispersion wavelengths have been achieved, with dispersions of 0 ps / (nm·km) at wavelengths of 1278nm, 1566nm, and 1645nm, and only -60 ps / (nm·km) at 1550nm, which is conducive to accurate and stable signal transmission.

[0011] The novel photonic crystal optical fiber of the present invention has a simple structure and is easy to integrate and process. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The schematic diagram of the cross-section of the novel photonic crystal fiber structure in a specific embodiment is shown in the figure: 1-base material; 2-circular air hole in the cladding; 3-elliptical air hole in the cladding; r1-radius of the circular air hole; a1-long axis of the elliptical air hole, b1-short axis of the elliptical air hole; d0-hole spacing between adjacent air holes; d1-diameter of the fiber cladding.

[0013] Figure 2 FIG. 1 is a graph showing the relationship between the birefringence of the novel photonic crystal fiber and the wavelength when the radius r1 of the circular air hole takes different values ​​in a specific embodiment.

[0014] Figure 3 : is a graph showing the relationship between the dispersion and wavelength of the novel photonic crystal fiber in a specific embodiment when the radius r1 of the circular air hole takes different values, wherein:

[0015] Figure 3a is the dispersion in the x-polarization direction, Figure 3 b is the dispersion in the y polarization direction. DETAILED DESCRIPTION

[0016] The present invention will be further described in detail below with reference to the accompanying drawings and by way of examples. The following examples are intended to explain the present invention but the present invention is not limited to the following examples.

[0017] Figure 1 The figure shows a cross-sectional schematic diagram of the novel high birefringence photonic crystal fiber of the present invention, wherein the base material 1 is silica. The cladding air holes are distributed in an axisymmetric manner as a whole, and there are 5 layers of air holes on the left and right sides of the fiber core, respectively. The innermost layer of the cladding air holes is composed of elliptical air holes with a major axis of a1 and a minor axis of b1 arranged in a hexagon, and the major axis of the elliptical air holes is perpendicular to the x-axis. The second layer is composed of circular air holes with a radius of r arranged in a hexagon. The part of the second layer of air holes located on the left side of the y-axis is sequentially translated to the left by d0 to obtain the 3rd to 5th layers of air holes on the left side of the y-axis of the cladding, and the part of the second layer of air holes located on the right side of the y-axis is sequentially translated to the right by d0 to obtain the 3rd to 5th layers of air holes on the right side of the y-axis of the cladding, and the fiber diameter is d1.

[0018] In this embodiment, the photonic crystal fiber structural parameters are as follows: the circular air hole radius r1 is 0.35 μm, 0.38 μm, and 0.4 μm respectively, the major axis a1 and minor axis b1 of the elliptical air hole are 0.8 μm and 0.4 μm respectively, the air hole spacing d0 is 0.85 μm, and the fiber cladding diameter d1 = 9.4 μm.

[0019] The present invention can use the finite element method and combine the perfect matching layer boundary absorption condition to perform theoretical calculations to obtain the birefringence characteristics and dispersion characteristics of the present invention.

[0020] In this embodiment, the birefringence characteristics of the photonic crystal fiber obtained when the circular air hole radius r1 is 0.35 μm, 0.38 μm, and 0.4 μm are as follows: Figure 2 As shown, observe Figure 2 We can get:

[0021] The birefringence of the novel high birefringence photonic crystal fiber of the present invention increases with the increase of r1. At the commonly used communication wavelength of 1550nm, when r1=0.4μm, the birefringence can reach up to 4.477×10 -2 The birefringence of ordinary optical fiber is generally 10 -4 The birefringence of existing photonic crystal fibers is generally 10 -3 It can be seen that it is 1-2 orders of magnitude higher than the existing photonic crystal fiber, which reduces the coupling of the transmission signal in the two polarization directions. It plays an important role in high-speed optical communication systems, optical fiber sensing and other fields.

[0022] In this embodiment, when the radius r1 of the circular air hole is 0.35 μm, 0.38 μm, and 0.4 μm, the dispersion characteristics of the photonic crystal fiber in the x and y polarization directions are as follows: Figure 3 (a) Figure 3 As shown in (b), observe Figure 3 We can get:

[0023] The novel high-birefringence photonic crystal fiber of the present invention has three zero-dispersion wavelengths in the x-polarization direction, namely 1278nm, 1566nm and 1645nm, and the dispersion value at 1550nm is only -60ps / (nm·km). The smaller dispersion is conducive to the generation of supercontinuum spectrum and the accurate and stable transmission of optical signals. The y-polarization direction has negative dispersion values, which can offset the positive dispersion in the required communication system by adjusting the structural parameters or wavelength to achieve the function of dispersion compensation.

[0024] The above is only one embodiment of the present invention, not all or the only embodiment. Any equivalent changes made to the technical solution of the present invention by ordinary technicians in this field after reading the specification of the present invention are covered by the claims of the present invention.

Claims

1. A novel photonic crystal fiber with high birefringence and multiple zero dispersion wavelengths, wherein the cross section of the fiber includes a cladding and a core, and is characterized in that: There are 5 layers of air holes on the left and right sides of the core of the photonic crystal fiber, respectively. The innermost layer of the cladding air holes is composed of elliptical air holes with a long axis a1 and a short axis b1 arranged in a hexagon, and the long axis of the elliptical air hole is perpendicular to the x-axis, and the ratio of the long axis a1 to the short axis b1 of the elliptical air hole is 2:1; the second layer is composed of circular air holes with a diameter of 2r1 arranged in a hexagon, and the part of the second layer of air holes located on the left side of the y-axis is successively translated to the left by the same distance d0 to obtain the 3rd to 5th layers of air holes on the left side of the y-axis of the cladding, and the part of the second layer of air holes located on the right side of the y-axis is successively translated to the right by the same distance d0 to obtain the 3rd to 5th layers of air holes on the right side of the y-axis of the cladding, and the overall structure is axially symmetrically distributed.

2. A novel photonic crystal fiber with high birefringence and multiple zero dispersion wavelengths according to claim 1, characterized in that: In the above parameters, the diameter of the circular air hole is equal to the major axis length of the elliptical air hole, and the hole spacings between adjacent air holes are equal.

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