Research On Tunable Comb Filters Based On Hibi Fiber Sagnac Loops

Optical fiber communication becomes the focus of modern communication technology because of its advantages such as large capacity, high noise immunity property, strong security. Tunable optical filter in optical communication field has a very wide range of applications, especially in tunable fiber lasers.The applications of tunable filters can reduce the system's operation and backup costs greatly, so they are valuable. Tunable filters must possess some properties such as large tuning range, tuning flexible, low insertion loss, short tuning period to reach the required of the application optical fiber communication.And the interferometers based on High Birefringence (HiBi) fibers and Sagnac loops have many advantages, such as narrow line width, polarization independence, low insertion loss, easy to fabrication, cost effectiveness, and so on. Optical filters fabricated using HiBi fiber Sagnac loops have the ability of wide tuning range and high tuning flexibility, so it receives much concern. Researchers have attached important to the filters constructed by high-order interferometers because of its properties such as tuning flexible, tuning flexible.This thesis build a system model for tunable fiber filters based on HiBi fiber Sagnac loops, and design two kind of tunable filters which based on HiBi fiber and Sagnac interferometers. According to the demand of tunable fiber filter, the optical properties, tuning methods, and the design of tuning mechanisms of the Sagnac loop based filters were analyzed theoretically and numerically. The main works are summarized as follows:1) In-depth analysis the researches at home and abroad, which of tunable filter and interferometers based on HiBi fiber Sagnac loops. According to this, compare various tunable filters, clear the research value of tunable filters based on HiBi fiber Sagnac interferometers.2) The transfer function of single-stage HiBi Sagnac interferometer was derived, Based on which, the system model of the Sagnac loop based filters was build and the output spectra were simulated. According to the results of simulation, the impactions induced by the parameters of each component of the interferometer, was analyzed.3) The system models of high-order HiBi Sagnac interferometer were built. The optical characteristics of Solc-Sagnac interferometer and Lyot-Sagnac interferometer were simulated and analyzed, the good combinations were found.4) A method for tuning the output spectra of various Sagnac loop based optical filters was proposed, which is based on the PZT technology. The tuning feasibilities were analyzed by employing the theory of elasto-optical effect and piezoceramics.5) Two kinds of combined high-order tunable filters were studied. The optical properties and the tunability of the filters were numerically demonstrated.