Research On Modulation And Demodulation Technology Of F-P Fiber Interferometer

With the rapid development of ultra-precision manufacturing industry,the demand for miniaturized and high-precision displacement measurement is increasing day by day.Optical fiber interferometry is being studied and applied more and more because of its high precision,strong anti-interference and high environmental adaptability.Compared with other types of fiber-optic interferometers,Fabry-Perot(F-P)fiber-optic interferometers are more simple and reliable in structure and can adapt to more complex environment,which has become a key research project of many countries.For interferometric phase measurement,the performance of phase measurement system is directly related to the demodulation method.Phase Generated Carrier(PGC)is a kind of commonly used homodyne modulation and demodulation method,which has the advantages of high sensitivity and simple demodulation and is widely used in optical fiber interferometry.However,the traditional PGC modulation and demodulation scheme lacks complete precision model analysis,and does not give the influence of modulation depth,modulation carrier frequency and other key parameters on the performance of the demodulation system,which brings difficulties to the design of the modulation and demodulation system for specific performance indicators.In addition,due to the response time of the laser modulation time,analog circuit,photoelectric detector conversion factors such as delay time,need to input relative to the modulation signal demodulation of interference signals output inevitably exist a phase delay,leading to understand the signal fading problem,in the process of the phase delay when the Angle is 15 ° will be introduced as high as 3.09 ° phase measuring error,restrict the improvement of the accuracy of measurement.Due to the above reasons,it is of great significance to study the precision model and phase delay compensation method in PGC modulation and demodulation for the field of optical fiber interferometry.Under the above background conditions,the following aspects are studied in this paper:(1)In view of the existing PGC demodulation scheme for lack of a complete system error model of the problem,this paper analyzes the principle of PGC modulation and demodulation process,the modulation depth,the ADC sampling rate and modem system of displacement measurement parameters,such as performance index are derived,the relationship between the establishment of a complete PGC demodulation mathematical model,established the demodulation system the function of each module division and distribution of precision.(2)In view of the signal fading problem caused by the phase delay in the demodulation process of PGC,this paper analyzes the action form of measurement error introduced by the phase delay,proposes an adaptive phase delay compensation algorithm,which can automatically detect and compensate the current phase delay amount of the modulation and demodulation system.After testing to compensate the phase measuring error introduced by the phase delay is superior to the 0.019 °.(3)The digital PGC modulation and demodulation system based on FPGA highspeed signal processing is designed,the high-speed sinusoidal modulation output unit is designed by using DDS technology,the test optical path of the F-P fiber interferometer is built,and the experimental test platform of the PGC modulation and demodulation system is established.The dynamic range,resolution and precision of the electrical signal and the resolution of the high precision displacement table are tested respectively.The test results of electrical signals show that the displacement measurement speed of the digital PGC modulation and demodulation system designed in this paper is better than 122.8mm/s,the displacement resolution is better than 0.11 nm,and the displacement measurement accuracy is 0.10 nm.The effective resolution of the displacement table is better than 0.4nm.