The Study On The Demodulation Methods Of Optical Fiber Fabry-perot Pressure Sensor Based On Spectrum Demodulation

Diaphragm based optical fiber Fabry-Perot(F-P) pressure sensor can be directly modulated the pressure on the Fabry-Perot cavity length ,because its sensitivity is high, the method has a wide range of applications in the petrochemical and aviation and other fields. To obtain small variation of F-P cavity length , a lot of demodulation methods have been proposed , in which the phase demodulation method based on spectrum has get more attention. In this paper, semiconductor optical amplifier (SOA) and optical fiber F-P tunable filter constructed spectral experimental systems for studying on demodulation method. the method easy to implement F-P sensor multiplexing, and to combine with the fiber grating sensing technology , this paper studied on such problems as the peak wavelength detection error, the jump of interference-order.The main work listed as following is completed in this paper.1、The output spectrum characteristics both of sensor with one cavity and Cascade cavity is analysed with the help of the theory of multi-light interference, In the spectrum demodulation algorithm method the theory and demodulation accuracy factors of single peak method, double-peak method and multi-peak method have been studied.2、The experimental system of F-P pressure sensor system is designed. Fiber ring laser is set up by SOA and tunable Fabry -Perot filter, fiber F-P etalon design is selected to set up the reference light path to get wavelength. Otherwise Experimental data was processed with the help of NI data acquisition card and Labview software.3、In the spectrum demodulation system , peak detection algorithm has been studied and simulated, at last the method based on polynomial fitting algorithm has been used in this system. A novel algorithm based on fitting of interference-order is proposed to calculate the sensor’s cavity length and is verified in simulation.In addition, the spectrum of the cascade optical fiber fabry-perot pressure sensor was anylised, the study show that the lower envolope of the spectrum can be used to demodulate the sensor’s cavity length4、In experiment system ,the application of spectrum demodulation algorithm is discussed. First, the characteristics of the experimental system is test ,the light output spectral range 1535-1590nm, the optimal scanning frequency is below 10Hz.and then the sensor parameter measurement, pressure testing, demodulation method validation were researched in experiments separately from F-P pressure sensor with one cavity and Cascade cavity, experimental results show the sensitivity of two sensors were 6.11nm/kPa and 19.664nm/kPa.