Fiber-Optic Sensors Using Photonic Crystal Fiber

Abstract

In this thesis, fiber-optic sensors based on Sagnac interferometer using photonic crystal fiber (PCF) are addressed from the fundamental concepts to the result of their simulations and demonstrations. In chapter 1, the basic concept and the principle of the fiber-optic sensor and its applications that are commonly used are explained. The PCF is also classified into several classes according to its waveguiding principle and structure. In chapter 2, Sagnac interferometer will be discussed. The principle and properties of the optical fiber Sagnac interferometer is addressed. The simulation for the Sagnac interferometer was performed using MATLAB. The purpose of the simulation was to find the relation between the peak-wavelength shift and the change of birefringence. The simulation results showed that the peak-wavelength shifted toward longer wavelength increasing birefringence; to find the relation between the length of birefringent fiber and the spectral width of transmission spectrum-the result showed that the shorter length, the wider spectral width; and to check if the peak-wavelength shift is dependent on the region of sensing fiber perturbation applied or not-it was independent of the region of perturbations. These simulations gave us more assurance to analysis the experimental result. In chapter 3, three types of sensors have been demonstrated by using Highly birefringent Photonic Crystal fibers (Hi-Bi PCFs) such as torsion sensor, curvature sensor, and transverse force sensor. They employ almost the same components and the same setup for sensing the torsion, curvature, and transverse force. But the perturbation applying method and the sensing fiber (two samples were used with different length for different measurement) are slightly different. It showed that the Sagnac interferometer-based sensors are flexible. The sensitivities in measurement for the torsion, curvature, and transverse force showed roughly constant. In chapter 4, the distributed transverse force sensor is demonstrated by using a 90° twisted Hi-Bi PCF. Transverse force induced-birefringence was different depending on the location of the sensing fiber. The peak-wavelength shifts vary with the location.