Study On The Optical Fiber Fabry-Perot Sensors And Their Multiplexing

As a kind of high-precision interferometric optical fiber sensor, the Fabry-Perot (F-P) interferometric optical fiber sensor has won wide attention for its small size, compact configuration, good reliability and flexibility, immunity to electromagnetic interference, high adaptability in harsh environments, remote signal processing and the possibility of multiplexing. It has been widely used in civil engineering, oil well monitoring, aerospace, medicine and biology. In this dissertation, two types of Fabry-Perot interferometric optical fiber sensors are designed, fabricated and multiplexed. The main research works are outlined as followings:At first, intrinsic Fabry-Perot interferometric(IFPI) fiber sensors of low power loss are fabricated by fused splicing and coating in vacuum, thin gold deposited films used as partial reflectors. They are good candidates for multiplexed sensors networks. Then the mechanism of IFPI optical fiber sensors on the stress and temperature is discussed in detail and the corresponding experiments are carried out. To an IFPI optical fiber sensor with the cavity length of 357.675um, the experimental data indicate that the temperature sensitivity is 2.42nm/℃when the temperature varies from room temperature to 250℃and the stress sensitivity is 0.28 nm/μεwithin the range of 400με. The results, coincided with the theoretical analysis, imply that the IFPI optical fiber sensors can match different measurement conditions by optimizing the cavity length.After that, extrinsic Farby-Perot interferometric(EFPI) optical fiber sensors used for temperature or pressure measurements, are fabricated by using CO₂ laser thermal fusion method. Considering the diverse thermal expansion coefficient of individual material, multi-mode fiber and glass fiber are applied as reflecting fiber of the F-P sensor to design an low temperature and pressure cross-sensitivity EFPI pressure sensor and an EFPI temperature sensor respectively. Benefiting from the novel design, the sensitivity of the EFPI pressure sensor reaches 24.8nm/Mpa and the sensitivity of the EFPI temperature sensor is up to 22.3nm/℃.Finally, the serial frequency division multiplex (FDM) system based on IFPI and EFPI optical fiber sensors are represented. From the discussion of the FDM principle and corresponding simulations, the FIR band pass filter combined with the correlation demodulation fitting to analyze the superposed signal from the IFPI and EFPI sensors. In fact, the Hamming window conduces to suppressing the crosstalk between the two sensors in signal processing. The experimental results show that the crosstalk of the multiplexed system is limited below 0.1%.