Research On Key Technologies Of Laser Frequency Scanning Interference Absolute Distance Measurement

With the rapid development of aerospace,marine,and precision manufacturing,the ranging technology is required.Laser frequency scanning interferometer has advantages of non-contact,non-blind distance and no need for cooperated target in absolute distance measurement.So it becomes a research hotspot in this field.The ranging accuracy of the laser frequency scanning interference absolute distance measurement is increased with the increase of the laser tuning range.However,the measurement accuracy is difficult to be further improved due to the limitation of the frequency modulation bandwidth of the semiconductor laser at present.Then,the measurement accuracy of the laser frequency scanning interferometer has been greatly improved by the appearance of the broadband external cavity frequency modulated laser.However,the use of broadband external cavity tunable laser for ranging system has brought new problems,for example the form of external cavity laser frequency modulation non-linearity is high-order function,which makes correct frequency modulate non-linearity difficult.Wideband frequency modulation also brings problem of dispersion mismatch which leads to ranging precision decrease,large amount of measurement data demands for fast frequency estimation algorithm.These problems have become the factors that limit the measurement of broadband laser frequency scanning interferometry.In view of the above key issues,the paper conducts research into broadband laser frequency scanning interference absolute distance measurement system based on frequency sampling method.The main research contents of this paper are as follows.The broadband external cavity laser frequency scanning interfere measurement system is built.By analyzing frequency modulation non-linear characteristics of external cavity laser,the set of frequency sampling method is used to correct the beat frequency signal nonlinearity.Correction of high order tuning nonlinearity is realized by the method.Due to the limitation of the Nyquist sampling theorem,the measurement range of frequency sampling method can not exceed 1/2 of the auxiliary interferometer.To extended measurement range,the paper puts forward the phase shift frequency sampling method.The measuring signal is phase shifted in accordance with the auxiliary interferometer phase scale that making phase shifted signal satisfies the Nyquist sampling theorem.The experimental results show that the range expand of 7 times.The impact of dispersion mismatch between optical fiber auxiliary interferometer and the measured path to ranging precision is studied.It found that with the frequency modulation bandwidth and distance increases,the quantity of measurement signal beat frequency increases linearly with time,leading to the target spectrum broadening and measurement error.This paper established the theoretical model of dispersion mismatch between optical fiber auxiliary interferometer and the measured path.To compensate the dispersion effect of the measurements,the proposed dispersion compensation based on chirp slope calibration method.The method effectively reduces the target spectral peak broadening effect and can make the target peak full width at half maximum(FWHM)basically reach the level of close to the theoretical value after dispersion compensation.Due to the great tuning bandwidth of broadband laser,a single measurement of the amount of data formed by broadband laser will increase with tuning range.It leading to the existing beat frequency extraction algorithm efficiency decreased.This paper studies the characteristic of beat frequency extraction algorithm,and puts forward the beat frequency extraction algorithm.By frequency shift,down sampling of the measured signal,which can maintain fastest computing speed.The accuracy of the algorithm is same to that of the multiple modulation zoom spectrum analysis based on multiple analytical band-pass filter(ZFFT)algorithm,and the computation time is 27.4% of the ZFFT algorithm.Secondly,frequency extraction of the linear regression method based on phase method is studied.The simulation results indicate that the algorithm has the ability of high precision frequency measurement in the condition of high signal to noise ratio.The influence model of temperature on the optical fiber auxiliary interferometer is studied.Then,the influence of temperature on measurement is reduced by method of model parameters compensation and optical path correction.Finally,the experimental results show that the extended uncertainty of the absolute distance measurement is less than U=(7.6×10-6+2.8×10-6Rm)m(k=2)that in the 12 meters range.