The Study On The Theory And Experiment Of Tunable Fiber Fabry-Perot Filter

Optical tunable filters have been considered as one of critical components in dynamic dense wavelength division multiplexing (DWDM) networks. They can provide the required wavelength for the receiver to establish the communication links. Also they can be combined into intelligent, efficient and stable optical modules with other components. Therefore, they are helpful for the flexibility, efficiency and cost of the dynamic DWDM networks. Due to the advantages of narrow bandwidth, large tuning range and high tuning speed, tunable fiber Fabry-Perot (FFP) filters have attracted much attention. In this dissertation, optical transfer properties, tuning characteristics, wavelength tracking and locking applications of the tunable FFP filters have been investigated thoroughly. The main contents are as follows:(1) The relationship between the insertion loss and the peak transmission as well as the finesse of Fabry-Perot (FP) interferometer is analyzed based on the basic theories of the multiple beam interference. The peak transmissions of tunable FFP filters, the transfer property of FP interferometer driven by linear voltage, and the time domain response of the filter with Lorentizan spectrum driven by alternating voltage are derived are analyzed simulatedly. These can be considered as the theoretical basis to investigate e tunable FFP filters in the following chapters.(2) In the cases of infinite mirror size and finite mirror size of air gap type tunable FFP filter, the insertion losses (IL) including the diffraction loss and the mode field coupling loss between the fiber-mirror and the mode of single-mode fiber (SMF) are studied systematically. Combining with the mode mismatch loss between the air gap resonant mode and the mode of SMF regardless of the mirror optical boundary, the theory of IL of tunable FFP filer with arbitrary mirror size is supplemented.(3) A novel design of the tunable FFP filter is proposed. Based on analysis of the diffraction loss and the mode coupling loss between the mirror mode field and the mode of SMF, the optimum mirror size corresponding to the maximum peak transmission is obtained. The spectral properties of reflection and transmission are simulated by using a bi-directional beam propagation method for different situations of tunable FFP filters. And the results demonstrate that the IL of the FFP filter can be improved by selecting the fiber-mirror radius to be about 2-3 times of fiber-core radius. Therefore, a novel design for reducing the IL of the tunalble FFP filter is presented. Meanwhile, the effect of finite mirror size on the IL and practical factors of waveguide mixed air gap type tunable FFP filter are also simulated and analyzed.(4) Static tuning characteristics of a tunable FFP filter are investigated experimentally. The three methods of measuring the cavity length-voltage are compared including the peak-to-peak method, the two adjacent peaks method and the synthesis method. Static tuning characteristics of a tunable FFP filter are measured with the synthesis method. The effects of a tunable FFP filter on the side band and high frequency harmonics have been also investigated experimentally.(5) An impulse response method and Fourier transformation is proposed to theoretically analyze the dynamic characteristics of tunable FFP filter. The dynamic optical spectrum and time domain characteristic of a FFP tunable filter modulated by an alternating current (AC) dithering signal are derived. The simulated and experimental results show that the method can be used to determine the relation between the ac signal parameters and dynamic response through either the output optical signal or the output electrical signal.(6) Dynamic tuning characteristics of a tunable FFP filter are investigated experimentally. The phase frequency characteristics of tunable FFP filter is described by the dynamic time domain model by introducing a factor of PZT delay time, and a simple and accurate measuring method is propsed to measure the phase frequency of tunable FFP filter. And the frequency response including the phase frequency response and amplitude frequency response is measured. The resonant frequency and the working frequency range of the tunable FFP filter are determined. Instantaneous responses of tunable FFP filter with different amplitudes of step function are also measued and discussed.(7) For applications of wavelength scanning and locking, a controller of tunable FFP filter is designed. Through analysis of the time delay of open loop circuit and PZT, and the time constant of the closed-loop system, a wavelength measurement method utilizing the time difference between the theory time and measured time of the output signal is presented. The experimental results show that relative error of wavelength measurement is lower than the resolution ratio of optical spectrum analyzer at the scanning mode, and the preferable locking precision is obtained under the short-time stability with the designed wavelength controller. A digital controller based on MCU (Microcomputer Unit) for improvement is also designed. Finally we propose a design based on FPGA and adaptive filter algorithem.