Research On Some Key Issues And Precision Evaluation Method Of Frequency Scanning Interferometry

High-precision and high-accuracy measurement has been a topic of constant study in the field of metrology.As time goes on,the pace for seeking a method of higher precision and accuracy measurement has never stopped.At present,the re-quirements of high-speed,multi-target,high dynamic range,high-precision,and high-accuracy seem to be a shared vision in various fields,such as manufacturing,aerospace,biomedical etc.Frequency scanning interferometry(FSI),as a promising measuring method,has proved to be an efficient method in the high-precision and high-accuracy ranging fields.In this thesis,the principle of absolute distance meas-urement and some key issues of frequency scanning interferometry technique are deeply investigated.Meanwhile,a new precision evaluation method for measuring the absolute distance using FSI is also presented.We analyze the frequency-sampling error based on k-clock method—an inter-ferometer that is used to trigger photocurrent sampling at time intervals that corre-spond to equal steps in optical frequency,and identify that the precision and accuracy are affected by two factors,namely,fiber length of auxiliary interferometer and sam-pling errors.To calibrate the fiber length and eliminate the sampling errors,a method based on molecular absorption line is proposed.After calibration,the length accuracy is below±150?m with a fiber length of 55 m,corresponding to a relative precision of5.5 ppm,which is better than the precision calibrated by the reference interferometry.In the experiments,when the distance is up to 8.7 m,the precision of absolute dis-tance is improved by 2 times.We analyze the vibration effect on the FSI distance measurement precision,and perform two consecutive measurements with same values of sweep duration and sweep range to remove the influence of drift.Meanwhile,the models of a sinusoidal vibration and uniform motion are derived and verified by experiments.Under condi-tions of active sinusoidal vibration,when the frequency is below 10 Hz,the precision of absolute distance is improved by 62 times with proposed method.Moreover,the precision is improved by 23 times in natural environment.We propose a combined FSI autofocusing system and a fast compensation method for dispersion mismatch,which could allow high-precision ranging to be per-formed at a long distance.By using the dual-beam laser autofocusing system based on a liquid lens,this system can quickly complete a measurement with high-precision.The experimental results showed that the measurement uncertainty is 4.03?m+2.05?m/m?R_air(k=2)within a range of 1m to 60m.We present a precision evaluation method of measuring the FSI absolute distance based on two-fiber interferometer.A lower Cramer-Rao lower bound on the variance of distance parameter of the resampled signal in the presence of noise is derived.It shows that the precision of absolute distance is affected by the signal-to-noise ratio of the system and chirp bandwidth.Particularly,this precision evaluation method is not restricted to any distance estimation algorithm.This result is verified experimentally.In the large-bandwidth and long-distance measurements,we propose a novel fre-quency estimation method,multiple signal classification(MUSIC),to be used instead of the conventional fast Fourier transform(FFT)-based algorithm to obtain better range precision.The experimental results have shown that the square error of distance using MUSIC estimator is much closer to the CRLB than conventional FFT-based method.Moreover,a simulation of range precision versus signal-to-noise ratio and bandwidth is also demonstrated.When the chirped bandwidth is equal to 2.2 nm and the signal-to-noise ratio of absolute distance measurement interferometer is raised to more than 70 d B,the obtained precision is below 10?m.This method can provide a theoretical reference for improving the precision of FSI distance measurement and it could be widely used in the future.