Design And Implementation Of Low Coherence High-speed Demodulation Of F-P Fiber-Optic Sensor

For their advantages of small size,high sensitivity and strong anti-interference ability,and so on,extrinsic fiber-optic F-P sensors have been widely used in biomedical sensing,chemical sensing,structural health monitoring and other fields.Especially,the applications in hash environments,such as high temperature,high pressure and strong radiation,have become one of the research focuses.For the real applications of these fiber-optic F-P sensors,the development of the demodulation technology is the key issue.In this dissertation,the principle and key techniques of low-coherence demodulation are studied systematically,which are also analyzed and compared with the intensity demodulation method,spectral method and polarization correlation demodulation method.The main research works are outlined as follows:(1)Based on the principle of low-coherence correlation demodulation,the corresponding mathematical model was built,and the signal analysis and simulation were carried out by combining with the interference principle of extrinsic fiber-optic F-P sensor.(2)The optical system of a low-coherence correlation demodulation system was built,and Powell lens was introduced into its linear spot shaping system.A cassette was designed to shield the interference of spatial stray lights on the correlation interference signals,by which,the practicability and stability of the system were improved.(3)According to characteristics and performance requirements of interrogation system,a hardware circuit was designed,which mainly includes power circuit,high-speed sampling circuit and high-speed linear array image sensor driver circuit.The signal processing of interrogation system was implemented in an FPGA chip.(4)According to the low coherence correlation demodulation method,an experimental system was built,and was tested through the interrogation of a fiber-optic F-P pressure sensor.A sapphire fiber-optic F-P sensor was assembled and tested.Based on the cross-correlation algorithm,the relationship of the cavity length versus the CMOS pixel serial number was gotten under different pressures and temperatures,and the data refresh rate of the low coherence correlation demodulation system can reach to 2 k Hz.