Study On Dual-Comb Displacement Measurement Based On Electronically Controlled Optical Sampling

Dual-comb time-of-flight(TOF)ranging method utilizes the inherent repetition rate difference between two lasers to realize asynchronous optical sampling(ASOPS)between optical pulses,which takes full advantage of ultrashort laser pulses’ ultrahigh temporal resolution and broadband coherent spectrum in the frequency domain.It has excellent comprehensive performance in terms of measurement rate,precision and range.Therefore,dual-comb TOF ranging method has attracted extensive attention in the fields of precise instruments manufacture,micro-scale structures detection,topography exploration,lidar,planetary detection.However,the update rate of the dualcomb TOF ranging method based on ASOPS technology is limited by the repetition rate difference,and the sampling process has no selectivity,resulting in low sampling efficiency.On the basis of the traditional ASOPS technology,this thesis adds the periodic electronically-controlled modulation to the repetition rate difference of dual combs to generate round-trip scanning between pulses,which effectively shortens the sampling interval and improves the sampling efficiency.The electrically controlled optical sampling(ECOPS)technology is applied to the dual-comb TOF ranging,thus the measurement update rate can be increased by adjusting the frequency of the driving signal of modulation device,further enhancing the practicability of dual-comb ranging method.The main contents of this thesis are as follows:1.Dual-comb TOF micro-displacement measurement based on ECOPS technology.The feasibility of ECOPS technology used in dual-comb ranging was theoretically explored,and the displacement calculation process and the maximum measurable distance were analyzed.The experimental setup of the displacement measurement system was carefully designed,and the structures and characteristics of each key module were introduced.The static displacement measurement was carried out in the range of 40μm,and the experimental results were in good agreement with the results of the standard laser interferometer.At an average time of 25.6ms,the measurement precision reached 26.1nm.2.Dual-comb TOF micro-vibration identification based on ECOPS technology.The vibration measurement system utilizing low repetition-rate dual combs detected the sinusoidal vibration applied to a piezo actuator with a frequency of 100 Hz and an amplitude of 24μm.The update rate was 10 k Hz.In order to measure higher-frequency vibrations and further improve the update rate,the above dual combs were replaced with two high repetition rate nonlinear polarization rotation(NPR)mode-locked lasers.The sinusoidal and triangular vibrations with a frequency of 100 Hz applied to a piezo positioning stage were recorded simultaneously by ECOPS-based vibration measurement system and the standard laser interferometer.The consistency of the two results reflected the accuracy of the vibration measurement system and the update rate reached 80 k Hz.The sinusoidal vibrations of a piezo actuator at a speed of 500 Hz and1k Hz were identified successfully,and the update rate up to 100 k Hz was obtained.