Research On Phase Compensation Technology Of Rough Target In Heterodyne Detection

Laser heterodyne detection technology is widely used in coherent Doppler lidar measurement,laser spectroscopy,optical fiber communication and other fields due to its advantages such as high conversion gain,good spectral filtering performance,and strong spatial and polarization discrimination capabilities.In the case of active laser detection,rough targets will cause the wavefront mismatch between the local oscillation light and the signal light on the detector surface,thereby significantly reducing the heterodyne efficiency.This is the outstanding problem of laser heterodyne active detection technology.This thesis mainly focuses on the decoherence phenomenon of rough targets in optical heterodyne detection,and carries out research work:This article introduces the basic principle of optical heterodyne detection,and on this basis,the decoherence effect formula is caused by the uneven surface of the target is derived in detail.Using the statistical parameters of the rough surface,the Monte Carlo method is used to simulate the rough surface of the actual heterodyne detection.The simulation results show that the root mean square height and correlation length are the main parameters that cause the decoherence effect.Aiming at the technical problem of phase distortion between local oscillator light and signal light,a new method for calculating the random phase compensation of the signal based on sequence shift and cross-correlation is proposed by using the array detector method.This method uses the array signal to perform cross-correlation calculations,and takes the 10 Hz external differential component in the total output signal spectrum as the objective function to quickly and accurately estimate the optimal sequence offset and calculate the compensation phase.The simulation results show that,compared with the intelligent optimization algorithm,the signal processing time of the proposed algorithm can reach the order of milliseconds,and the speed is increased by 10~4 times.In order to evaluate the compensation performance of the cross-correlation algorithm,the cross-correlation method is compared with the improved intelligent optimization algorithm,and the statistical results are used to objectively evaluate the fitness value.It is verified that even in the case of low signal-to-noise ratio,the convergence accuracy of the cross-correlation algorithm is higher,and the signal-to-noise ratio after processing is significantly improved.In order to verify the effectiveness of the cross-correlation algorithm to solve the decoher-ence problem,this paper builds a heterodyne detection experimental system based on the array detector method.In view of the fact that the heterodyne signal has a certain phase difference between two adjacent samples of the analog-to-digital converter,the time-domain phase difference is used to correct the spatial phase difference.The phase correction is achieved by moving the output sequence obtained by the detector elements in the array,and the steps of the movement depend on the number of spatial phase mismatches.The results show that this method can better compensate the decoherence effect caused by phase distortion.