| Interferometric fibre-optics sensor is related to fields of optics, photoelectron, exact mechanism, signal processing technology and so on. Developed countries make a point of doing this research because of its high sensitivity and big dynamic range. Interferometric fibre-optics sensor can realize precise, fast, the non-contact survey. Signal demodulation technique is one of its key techniques. And it directly influences resolution, precision, dynamic range and so on.This paper first elaborates the basic principle of interferometric optical fiber sensor, analyses Michelson interferometers with Farady rotator mirror. Second several kinds of demodulation technique are introduced completely, focused on part of them, analyses their merits and demerits, application situation and technical difficulty, also compares their main performance. Phase generated carrier demodulation is elaborated in detail, included two ways of PZT modulation and direct laser source modulation.This thesis focused on researching passive demodulation scheme using 3×3 couplers. It analyses the principle of quadrature and symmetric demodulation. It does some theoretical analysis and simulation about possible distortion and cause. Improved quadrature demodulation scheme is designed. Improved quadrature demodulation scheme is insensitive to fluctuations in light source intensity and can overcome the influence to the demodulation when the coupler is asymmetric. Against the problem of symmetric demodulation scheme, adjusting the gains of removing direct current circuit and automatic gain control circuit is to eliminate distortion caused by asymmetric three-road outputs. An improved symmetric demodulation scheme is proposed. It is replacing automatic gain control circuit with amplitude normalization processing. On the base of theoretical analysis, improved demodulation schemes are simulated Using MATLAB software. |
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