Study On Tunable Comb Filters Based On High Birefringence Fiber Sagnac Loops

With the increasing of optical channels in dense wavelength division multiplex (DWDM) systems, various optical filters related to DWDM applications become a hot research area in optical fiber communication. High birefringence (HiBi) fiber Sagnac loops attracted widespread attention in recent years due to their simple structure, stable performance and perfect comb filtering characteristics.In this thesis, the characteristics of basic HiBi fiber Sagnac loops are studied theoretically, based on which, various optical filters formed by HiBi fiber Sagnac loops with complex structures were studied and designed using numerical analysis methods. The major works are summarized as follows:1,First, the detailed reflection and transmission characteristics of HiBi fiber Sagnac interferometers are studied using Jones matrix theory, and the effects of the length and birefringence of the HiBi fiber, the state of polarization controller, coupling ratio, and states of polarization of the input fields on the transmission spectra are discussed.2,The characteristics of the Sagnac interferometer composed of multi-section HiBi fibers are studied theoretically. The transfer functions of multi-section HiBi fiber Sagnac interferometer are deduced theoretically, and the effects of various design parameters on the output spectra were analyzed and discussed.3,The spectral characteristics and design method of multi-wavelength filters, which are composed of a number of cascaded high-birefringence fiber Sagnac loops, are studied in detail.4,A tunable comb filter based on high-birefringence fiber Sagnac interferometers is analyzed and designed. The results show that the tunability of HiBi fiber Sagnac interferometer can be achieved by controlling the length birefringence of the HiBi fiber employing PZT technology.5,The widely tunable bandpass filters based on HiBi fiber Sagnac loops are theoretically analyzed and discussed.The results of above research show that many filtering functions can be achieved by using HiBi fiber Sagnac ring based filters. These filters not only have perfect multi-wavelength comb filtering characteristics but also can achieve tenability, and can find many potential applications in the fields of fiber sensor, tunable fiber lasers and DWDM systems.