The Study Of Optical Fiber Microphone System Based On White-light Interferometer

With the development of optical fiber sensing technology, white light interferometric fiber-optic microphone has become a hot research focus in sensing field. However, the phase sensitivity of white-light interferometric fiber-optic microphone appeared in literature are not very good. We study the phase sensitivity of the white-light interferometric fiber-optic microphone from theory and experiment, accordingly the operating phase point of the system is maintained atπ/2, which is proved the phase point with the highest phase sensitivity.In this paper two simple circuit demodulations for weak voice signal have been proposed by using white-light hybrid interferometer. The two hybrid interferometers are respectively based on fiber-optic waveguide modulator and a 3×3 coupler with dual balanced detection. The two demodulation methods achieve to make the system with the maximum phase sensitivity at the operating phase pointπ/2.The first chapter describes the development of fiber-optic microphone, and the fiber-optic microphone is divided into two categories in this paper. One category is the intensity modulated fiber-optic microphone, the other microphone is interferometric fiber-optic microphone. We describe the working principle of two fiber-optic microphones in detail. Meantime we introduce the main contents and innovation of this paper.In chapterⅡwe introduce the principle of optical interference principle and optical interference conditions, and then introduce the principle of white light interference, which provides a theoretical basis for the white-light interferometric fiber-optic microphone in chapterⅢand in chapterⅣ.In chapter III we study the fiber-optic microphone system theoretically and experimentally. The fiber-optic microphone system is based on a hybrid configuration of Mach-Zehnder and Sagnac interferometer. In this system, fiber-optic waveguide modulator overcomes the limitation in high frequency and nonlinear effect of PZT modulation, improves the flexibility of the system and the frequency response range. The experimental results of the fiber-optic microphone system based on fiber waveguide modulator have been demonstrated that the simple circuit demodulation for the weak voice signal is feasible.In chapter IV a simple fiber white-light interferometric demodulation method is presented and experimentally demonstrated. The balanced detection method is adopted in the experiment, the signal can be demodulated by subtracting the signals from the two detectors. The operating phase point of the system is maintained atπ/2, which is proved the phase point with the highest phase sensitivity. The theoretical analysis and experiment results demonstrated that the simple demodulation method has good performance.