Research On Some Key Techniques Of Fiber Optic Ring Interferometric Sensor

Following the fast development of fiber-optic communication technology,the fiber sensing technology has made great progress. Fiber optic ringinterferometric sensor (FORIS) is an important category of fiber optic sensor.It has been a success application of fiber optic gyro (FOG) because of its highsensitivity. In this dissertation, some key techniques of FORIS have beenresearched where the FOG has been taken as an example of FORIS. Theseproblems concern some key elements, like multi-function integrated opticchip (MIOC);the thermal effects on the MIOC and the FORIS. A novel signaldetection method for the re-entrant FORIS was also proposed in thedissertation. The research result of these techniques can help to drive theapplication of FORIS.The signal detection is always based on the phase modulation anddemodulation technology. The MIOC is a key element for phase modulation,which the half-wave voltage is one of the key modulation parameters. A novelmethod for measuring the half-wave voltage of MIOC was presented in thedissertation. The method is based on the linear frequency modulation (LFM)and heterodyne interferometric technology. It can avoid the shortcoming ofinaccuracy of the former methods. The measuring accuracy has been improved,as the error can be less than 1‰.The thermal effect is one of the main factors of influencing the FORIS.Because some of the key optical elements of FORIS are very sensitive to thetemperature fluctuation, the FORIS was affected in terms of the bias shift andscale factor instability. In this dissertation, the temperature characteristic ofMIOC was analyzed and was tested. A double loop structure was presented tocompensate the thermal induced effect on MIOC. The experimental resultsshow that the technology presented can restrain the bad effect on the scalefactor and the dynamic performance.Signal processing system and the data communication interface of FORISwas designed. Experiments have been done on the hardware of FORIS. As forthe software, programs of the FORIS, Re-FORIS and compensation of bias ofthe MIOC based on the DSP technology have been developed.Re-entrant FORIS is a new kind of FORIS in which parts of thecounter-propagating lights re-enter the fiber ring. The interferometric signalon the photo-detector is composed of interferometric signals ofcounter-propagating lights of different rounds of recycling in the ring. How todetect the needed signal from the general signal is very important for thesensor to be applied in the real field. A particular signal detection method isproposed in this dissertation. The signal detection method can separate thesignal of interferometric signals for certain rounds of recycling. Theexperiments show that the signal of 1 round of recycling and 2 rounds ofrecycling can be detected. And the signal detection method can be employedto get the measure results for a Re-FORIS.