Research On Broadband Sweep Frequency Interferometry Based On Semiconductor Laser

High-precision and high-efficiency measurement and detection methods are required for aircraft shell manufacturing,aircraft design,and ship shape shaping.The laser swept interferometry method has the advantages of high accuracy,non-cooperative target measurement,and the ability to measure targets in all directions at all angles,and because the swept interferometry uses heterodyne interferometry,it can obtain higher signal-to-noise In recent years,it has become a research hotspot in the field of absolute distance measurement.For the ranging system,the ranging accuracy is proportional to the frequency sweep bandwidth,and the accuracy of the ranging system can be improved by increasing the frequency sweep bandwidth.This paper focuses on the method of expanding the frequency sweep bandwidth of semiconductor lasers,and realizes the frequency sweep measurement of broadband by means of spectrum splicing.This paper proposes two different ways to extend the frequency sweep bandwidth for two kinds of semiconductor lasers,DFB laser and array DFB laser.The main research contents of this article are as follows:(1)Study the principle of swept-frequency interferometric ranging,and use frequency sampling method and iterative algorithm pre-correction to perform frequency-sweep nonlinear correction to eliminate spectral broadening caused by laser frequency-sweep nonlinearity.According to the principle and scheme of distance measurement,an experimental optical path was built to complete the frequency sweep experiment for two semiconductor lasers.(2)For the DFB laser,a combination of current and temperature is used.In the case of current frequency modulation,the temperature changes from 12°C to31°C.The external cavity laser was used to pre-calibrate the relationship between the phase change of the auxiliary path and the optical frequency change through the gas chamber,and then the measurement experiment was carried out.According to the absolute wavelength value of the gas absorption peak of the gas chamber signal and the phase change of the signal at different temperatures,the frequency sweep range of the laser at different temperatures can be obtained.Auxiliary signal is used to re-sample the measurement signal with equal optical frequency to eliminate nonlinearity.The resampled signal is spliced while meeting the phase matching principle without affecting the signal integrity and continuity.The sweep frequency range is increased from 0.5nm to 2.3nm,and the sweep frequency range is extended by 4.6 times.(3)For array DFB lasers,multi-tube cascading is used to expand the frequency sweep range.A very high current is applied to the array laser in a very short period of time to ensure that the frequency sweep ranges of adjacent tubes in the laser overlap without damaging the laser.The experiment using 5 adjacent tubes in the array to measure the auxiliary path length of 1.9392 m was completed.The standard deviation of single tube measurement is 1.6×10-5m,and the standard deviation of 5 tubes of continuous optical frequency stitching is3×10-6m.The frequency sweep range is extended from 3.8nm to 19 nm for a single tube,which is 5 times longer.