ANSYS-based birefringence property analysis of side-hole fiber induced by pressure and temperature

Photonic Sensors, Dec 2017

In this paper, we theoretically investigate the influences of pressure and temperature on the birefringence property of side-hole fibers with different shapes of holes using the finite element analysis method. A physical mechanism of the birefringence of the side-hole fiber is discussed with the presence of different external pressures and temperatures. The strain field distribution and birefringence values of circular-core, rectangular-core, and triangular-core side-hole fibers are presented. Our analysis shows the triangular-core side-hole fiber has low temperature sensitivity which weakens the cross sensitivity of temperature and strain. Additionally, an optimized structure design of the side-hole fiber is presented which can be used for the sensing application.

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ANSYS-based birefringence property analysis of side-hole fiber induced by pressure and temperature

ANSYS-Based Birefringence Property Analysis of Side-Hole Fiber Induced by Pressure and Temperature Xinbang ZHOU 1 Zhenfeng GONG 0 0 College of Physics and Optoelectronics Engineering, Dalian University of Technology , Dalian, 116024 , China 1 School of Ocean Science and Technology, Dalian University of Technology. Panjin , Panjin, 124000 , China In this paper, we theoretically investigate the influences of pressure and temperature on the birefringence property of side-hole fibers with different shapes of holes using the finite element analysis method. A physical mechanism of the birefringence of the side-hole fiber is discussed with the presence of different external pressures and temperatures. The strain field distribution and birefringence values of circular-core, rectangular-core, and triangular-core side-hole fibers are presented. Our analysis shows the triangular-core side-hole fiber has low temperature sensitivity which weakens the cross sensitivity of temperature and strain. Additionally, an optimized structure design of the side-hole fiber is presented which can be used for the sensing application. Fiber optics; birefringence; pressure measurement; temperature 1. Introduction Elasto-optic and thermo-optic effects exist in all kinds of optical fibers, and both of them affect the birefringence property of the fiber under different pressures and temperatures. Nowadays, side-hole fiber has been widely used to pressure sensing [ 1‒6 ] because of its unique property such as high pressure sensitivity, low temperature sensitivity, and good temperature compensation capability [7]. However, there is no analysis about the optimized structure of the side-hole fibers. Most of these studies are confined to the side-hole fibers with circular holes, and the problem of cross sensitivity between the temperature and strain still exists. In this paper, we propose two novel side-hole fibers with rectangular holes and triangular holes. We analyze the birefringence property of the side-hole fibers under different pressures and temperatures. Comparing the influences of the shape, size, and position of the holes on the birefringence property of these three kinds of side-hole fibers, we demonstrate that the side-hole fiber with triangular holes is more suitable for strain sensing, because the triangular-core side-hole fiber has a lower temperature sensitivity, which solves the problem of cross sensitivity of temperature and strain very well. 2. Principle of birefringence The birefringence property of the optical fiber mainly includes two aspects, which are inherent birefringence and induced birefringence. Inherent birefringence is formed during the fiber fabrication process. Once the optical fiber is fabricated, it is difficult to change the inherent birefringence. The induced birefringence is caused by the change in external environment conditions. An anisotropic stress distribution is induced in the core of the fiber, which can further generate fiber birefringence via the photo-elastic effect. As a result, we can use the induced birefringence of the optical fiber to measure the external conditions such as strain, temperature, and refractive index. nx = nx0 + C1δ x + C2δ y (1) ny = ny0 + C2δ x + C1δ y (2) where nx0 and ny0 are the effective refractive indexes in the x and y directions of the core without ambient pressure, respectively, C1 and C2 refer to stress elasto-optic coefficients of the fiber, and δ x and δ y present the strains of the core in the x and y directions, respectively. The birefringence of the fiber is defined as follows [ 10 ]: B = nx − ny = (nx0 − ny0 ) + (C1 − C2 )(δ x −δ y ) . (3) From (3), we know that the relationship between the birefringence of the fiber and the strain difference in the x and y directions is linear. In other words, the birefringence property analysis of the optical fiber can be converted into the strain difference analysis of the core of the fiber. 3. Simulation results of ANSYS To numerically illustrate the influences of different pressures and temperatures on the birefringence property of side-hole fibers, we use the finite element analysis method [ 11 ] namely ANSYS to simulate the strain field distribution over the cross section of the fiber at a given pressure or temperature. 3.1 Effect of strain In this simulation, the side-hole fibers are in the liquid environment of 20 ℃, and the pressure of 1 × 105 Pa acts uniformly on the fiber surface. The birefringence properties of circular-hole, rectangular-hole, and triangular-hole side-hole fibers are compared. Through this simulation results, we get the optimal size, shape, and location of the holes of side-hole fiber, which exhibits a high strain sensitivity and a low temperature sensitivity. 3.1.1 Circular holes For the side-hole fiber with circular holes, we hope to find the suitable radius and position of the holes in order to realize the largest strain sensitivity. We define δ as the strain difference betwe (...truncated)


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Xinbang Zhou, Zhenfeng Gong. ANSYS-based birefringence property analysis of side-hole fiber induced by pressure and temperature, Photonic Sensors, 2017, pp. 1-9, DOI: 10.1007/s13320-017-0434-0