Research On Signal Demodulation Methodof The Fiber F-P Sensorbased On Rapid Cavity Length Estimation

Fiber optical sensors have the advantage of small size,high temperature resistance,immunity to electric-magnetic interference,high resistanceto corrosion,high sensitivity,intrinsic safety,remote sensing,multi sensor multiplexing and so on.Fiber optical sensors have been widely used in areas such as petroleum and chemical industry,bridge safety,electricity system.The optical fiber Fabry Perot(F-P)sensor perceives the measured physical quantity through changes of the cavity length with characteristics of compact structure,short cavity length of 100 ?m and high sensitivity.It could be used in point measurement.Ithas a great prospect in the practical application.Study the demodulation technology of Fabry Perot sensorshas a great impact on improving the detection accuracy of the fiber optic F-P sensor system and the output reliability.It also has the vital significance to promote the application and development of optical fiber F-P sensor.The works done in the article are as follows:1?A discrete gap transformation method(DGT)based on climbing search algorithm with variable step is proposed to solve the problem original DGT algorithm to reduce the calculation amount and realize high precision measurement with high speed.The signal is denoised by wavelet threshold denoising to remove the glitches in original spectrumfirst.Then the starting point for climbing is determined by fast cavity length estimation method.The cavity length is demodulated by searching the corresponding modulated gap of the largest discrete gap coefficient through climbing search algorithm with variable step.The climbing search algorithm with variable step reduces searching rangeby changing the search step in each climbing round for searching the peak.Through several climbing process,the resolution could reach nanometer.Compared with common search method,the climbing search algorithm with variable step reduces 3 orders of magnitude under the search precision of 0.1nm.The new algorithm reduces the computational complexity,and improves the measurement efficiency.2?Awavelet phase extraction cavity length demodulation algorithm is proposed.The cavity length of the EFPI sensor is demodulated through the phase information of interference spectra solved by continuous wavelet transform,and high demodulation precision could be achieved in F-P sensor with large cavity length.Using fast cavity length estimation method to estimate the scale search range of anot only reduces the computation amount,but also is equal to let the signal pass a bandpass filter to reduce the high frequency noise.The simulation result shows that the error is smaller when the cavity length is bigger.The error is less than 10 nm especially when the cavity length is larger than 100?m.3?A fiber MEMS F-P sensor is designed and fabricated.DGT method based on climbing search algorithm with variable step and wavelet phase extraction cavity length demodulation algorithm are used to do the pressure calibrationexperiment to verify the correctness and practicability of the two algorithms.