The Study Of New Demodulation Algorithm For High Temperature Optical Fiber Fabry-Perot Sensor

Optical fiber Fabry-Perot sensor optical fiber F-P sensor has many advantages over traditional sensors,such as small size,simple fabrication,anti-electromagnetic interference,high resolution,and can measure a variety of physical parameters,etc.It has been widely used in metallurgy,energy,chemical,aerospace and other fields.Ordinary fiber-optic F-P sensors cannot perform high-temperature measurements due to the material properties of quartz fibers.The sapphire fiber not only has excellent high temperature resistance,but also has the light transmission characteristics of the optical fiber.Combining sapphire single-crystal fiber and fiber Fabry-Perot temperature sensing technology,sapphire optical fiber F-P high-temperature sensor can meet the needs of high-temperature measurement.The slight change of temperature leads to a corresponding change in the cavity length of the fiber-optic F-P sensor,so the demodulation performance of the sensor cavity length directly affects the sensitivity and application of the sensor.The traditional demodulation algorithms,such as the fringe counting method and the Fourier transform demodulation method,all have their advantages and disadvantages.In this thesis,the improved algorithms of the original Fourier transform method and the joint algorithm of the minimum mean square error method FFT-MMSE are proposed,and applied to real-time demodulation system,at the same time proposed a virtual reference path interferometry VRI and MMSE joint demodulation algorithm.The joint algorithm solves the problem of “mode jumping” in the MMSE algorithm,with a resolution of 4.2 nm and a corresponding temperature of 2°C.The main work and main achievements of this paper are as follows:(1)The principle of the cavity length demodulation of the fiber-optic F-P sensor based on the Fourier transform method and the realization process of the demodulation cavity length of the minimum mean square error algorithm are analyzed.The advantages and disadvantages of the FFT and the MMSE algorithm are analyzed.(2)Based on the FFT-MMSE joint algorithm,an improved algorithm is proposed to solve the problem of “mode jumping” of the original algorithm.This improved algorithm is applied to the demodulator system,and the demodulation accuracy and stability of the system are experimentally studied.(3)A demodulation algorithm combining VRI and MMSE is proposed.The demodulation principle and demodulation error of VRI are analyzed.The experimental data show that the joint algorithm can theoretically solve the problem of “mode jumping” and can reach the nano-level demodulation resolution at the same time.(4)The experimental system was set up,and the improved algorithm based on FFTMMSE and the demodulation performance of VRI-MMSE combined algorithm were analyzed and summarized.The experimental results showed that both algorithms can achieve high-precision demodulation of high-temperature F-P cavity length.At the same time,the experimental study on the ability of the sensing system to recognize the rapid change of temperature was conducted.Through analysis of a series of experimental data,the system can identify the temperature change over 80°C/min.Finally,the content of this paper is summarized,and the shortcomings and methods of improvement are pointed out.