Research On Optical Filter Based On Birefringent Effect In Photonic Crystal Fiber

Wavelength Division Multiplexing (WDM) / Dense Wavelength Division Multiplexing (DWDM) are the key technologies to achieve high-speed and large-capacity transmission of optical fiber communication system. Stable tunable optical filter is one of the key devices in DWDM system. In this thesis an optical filter based on birefringence in photonic crystal fiber (Hi-Bi PCF) Sagnac loop interferometer is presented, which is supported by Tianjin Key Project of Applied and Basic Research Programs under Grant No. 043800911 and the Key Project of Ministry of Education under Grant No.206006. This filter has potential applications due to its advantages such as insensitive to temperature, wide wavelength span, tunable channel spacing and so on.The characteristics of Hi-Bi PCF are theoretical analyzed using full-vector finite-element method. In addition, a large amount of numerical simulations based on Jones matrix and experiments of the optical filter are taken, which is based on Hi-Bi PCF Sagnac loop interferometer. This thesis lays a foundation for further research and practical application of Hi-Bi PCF Sagnac loop interferometer.The main contents are as follows:First, a kind of Hi-Bi PCF with two big circular air holes adjacent to the core and squeezed hexagonal lattice is proposed. The characteristics such as birefringence, dispersion and temperature of the Hi-Bi PCF are studied using full-vector finite-element method. According to the research, the characteristics of the proposed PCF are as follows: 1) The phase modal birefringence of the PCF is 5.0×10^-3 at 1550nm and the group model birefringence of the PCF is 0 at long-wavelength, which are of great importance to minimize the impact of polarization mode dispersion (PMD) in telecommunication systems. 2) The x-polarization direction (along the large air holes) of the PCF has large negative dispersion at long-wavelength, whereas it has the positive y-polarized dispersion at the same wavelength. That can be used for dispersion compensation for single-polarization direction. 3) High temperature stability.Second, rigorous and systematic theoretical analyses of the transfer functions of the high birefringence fiber Sagnac interferometer are developed using Jones matrix method, and a great deal numerical simulations of Hi-Bi PCF Sagnac interferometer transfer functions have been taken.Third, a novel design of optical filter based on Hi-Bi PCF Sagnac loop interferometer is proposed. The temperature characteristics and channel spacing tuning of the filter are theoretically and experimentally investigated. The results show that the filter has many advantages such as insensitive to temperature, wide wavelength span, tunable channel spacing and so on.