Research On Absolute Distance Measurement Over A Wide Range Based On Dual Femtosecond Lasers

In recent years,the exploration of space field needs the support of space measurement technology urgently.Due to its advantages in peak power,repetition frequency and stability,femtosecond pulses can achieve high refresh rate and precision measurement of ultra-long distances,and it is regarded as an ideal light source in the field of absolute large-scale measurement.In this paper,we propose a mode-locking laser for the ranging system with nonlinear amplifying loop mirror and figure-of-9,and study pulse shaping of the erbium-doped fiber soliton laser theoretically and experimentally.Based on this laser,we design a long absolute distance ranging system with dual femtosecond short-pulse to achieve the measurement in the space field.The main contents include:The main components of the mode-locking laser are summarized,and the mode-locking mechanisms,nonlinear amplifying loop mirror and nonlinear optical loop mirror,are deduced.The effects of figure-of-8 and the figure-of-9 on the laser stability and pulse characteristics during the mode-locking process are introduced.The master oscillation equation is deduced by lumped description method,theoretical models of soliton mode-locking fiber lasers regarding different saturable absorbers functions were also established respectively.Mode-locking process and intracavity evolution dynamics of soliton fiber lasers were investigated.The pulse shaping theory of mode-locking fiber laser and the most important factor affecting the accuracy of ranging system,time jitter,are introduced.The applicable scenarios of various ranging schemes are summarized and the related theory of long-distance ranging scheme based on pulse echo and balanced optical cross-correlation are introduced.The computational methods of optical equivalent sampling and coherent measurement of double femtosecond pulses are studied,and this shows that the ultra-longdistance ranging system proposed in this paper is scientific and easy to operate,and strikes a balance between long-distance and high precision.The effect of time jitter on ranging accuracy is analyzed in simulation theoretically.Comparative experiments are carried out to study the effects of dispersion and resonator length on soliton shaping.The mode-locking femtosecond fiber laser is built,finlly,and the output pulse repetition rate is 47.8 MHz,spectral width is 38 nm,and time domain width is 114 fs.The ranging system achieves result error within 750 nm when the measured distance is 107 meters theoretically.Compared to other long-range absolute ranging systems,this system combines time-of-flight and phase to complement large range measuring.This system achieves sub-micronlevel errors in the 10,000-kilometer range,which greatly expands the range with high accuracy.The use of optical sparseness to detect echoes greatly reduces the computational complexity.The system has high academic and practical value,and provides an excellent case for the development of advanced laser ranging technology.