Fabry - Perot Sensor Demodulation Technique

Fiber-optic Fabry-Perot (F-P) sensor is a kind of high precision interferometric sensor, and this kind of sensor has a broad application prospect. F-P sensors can be classified into two kinds of sensors by their demodulation methods. One is intensity modulation/demodulation, and the other is phase modulation/demodulation. The intensity modulation method is the oldest and simplest method for fiber-optic sensor, in which a homochromatic laser is used as system light source. The advantages of method are simple principle and high sensitivity; while the disadvantage is that it is easy to be disturbed and is hard to control operation.At first, we studied the theory of multi-light beam interfeormetry. After analyzing the modulation/demodulation principle of intensity and phase for fiber-optic Fabry-Perot sensor, we present three demodulation methods: directive (intensity), in-directive (dual-wavelength) and four-wavelength demodulation aiming at MEMS pressure sensor.A technique for demodulating the fiber Fabry-Perot sensor is presented based on the dual-path and dual-wavelength demodulation principle. The dual-path sensor system is constructed. The Theoretical analysis, simulation calculations and experimental result are presented. It is proved that the method can eliminate errors resulting from wavelength-independent variations in the fiber interconnect to the sensor. The F-P displacement sensor system is designed and constructed. The MEMS pressure sensor is demodulated with four-wavelengh method and dual-wavelengh method, the comparison between two demodulation method is given. The result shows that the modulation and demodulation system is of highly precision and highly sensibility.Finally, some problems in the demodulation system and its improvement approach are discussed.