Beams Optimization And Steering Via Optical Phased Array

The coherent laser synthesis and beam steering accuracy based on optical phased arrays are affected by phase noise,which severely restricts their applications in laser synthesis,longrange laser communication,laser 3D imaging and biological endoscopic imaging.Research shows that the technology of adaptive optics can effectively compensate phase noise,improve output beam quality,and increase steering accuracy,which is one of the key technologies in optical phased array systems.This thesis focuses on the study of the optical phased array phase noise fast compensation method,and high precision beam steering voltage acquisition method,using theoretical analysis and experimental verification,to carry out systematic thesis.The content of this thesis mainly includes the following five aspects.1.Based on the Fronhofer diffraction theory,the far-field intensity distribution of the output beam of the optical phased array is numerically simulated,and its fundamental characteristics such as beam scan,beam width and beam scan range are analyzed.For the needs of beam phase noise compensation,the SPGD algorithm is utilized to optimize the beam,so as to improve the optimization efficiency.2.For the optical phased array system drive and beam optimization needs,the phase control system based on FPGA+DSP architecture is developed independently.This system uses FPGA for data interface control and DSP to execute optimization algorithm.The structure meets the speed of system beam optimization and accuracy requirements.A detailed analysis is given including the design ideas of each module,the process of implementing the SPGD algorithm and its performance.This system with channel expandability can accommodate different requirements of optical phased array system.3.In order to meet the requirements of fast beam optimization and high precision steering of fiber optic phased array system,this thesis studies the fast optimization of multi-beam and steering characteristics of optical fiber phased arrays by adaptive optics technology.One-dimensional 16-array fiber phased array system is built with the high-speed LiNb03 phase modulator,adopting the adaptive optimization algorithm of the SPGD.Besides,the "first correct,then steering" method is used to achieve the optimization and steering of multi-beam fiber phased array.Experimental results show that the single iteration time of SPGD algorithm does not exceed 10μs,the rejection ratio of the primary and secondary flap in output beam is close to the theoretical value,and the steering speed reaches 500kHz.Based on this,this thesis proposes the evaluation function value collector based on the SPGD algorithm and the surface array APD detector with efficient and high accuracy steering voltage acquisition.Experimental study using twodimensional 8×8 array fiber phased array,shows that the output beam quality and beam steering accuracy are as expected,which verifies the feasibility and effectiveness of the method.4.Optimization needs of output beam,especially for extremely weak light field intensity,in fast phase noise compensation for silicon-based optical phased array chips,are studied.A single-point APD detector is used as performance evaluation function value collector based on the SPGD algorithm to design the beam optimization measurement system.The experimental study is conducted with a one-dimensional 64-array non-uniform siliconbased optical phased array chip,and the experimental results show that the system not only can effectively achieve beam optimization,but also the optimization speed of single-pointing beam is improved from the traditional tens of minutes level to the order of seconds,and the efficiency is greatly improved.And the matching problem between the performance of the phase control system and the response characteristics of the silicon-based optical phased array chip is analyzed to improve the quality of beam optimization and effectively solve the beam optimization under weak light signals.5.In order to meet the demand for spectral detection application of silicon-based optical phased array chip,the study on multi-wavelength optical field synthesis and beam control based on silicon-based optical phased array chip is carried out,the theoretical model of multi-wavelength laser synthesis on silicon-based optical phased array chip is established,and the intensity distribution characteristics of the synthesized optical field after fully coherent synthesis and phase noise compensation using SPGD algorithm are simulated and analyzed.Experimentally,the one-dimensional 64-array silicon-based optical phased array chip 1535nm+1565nm dual-wavelength laser synthesis is studied to verify the theoretical results.According to the theoretical guidance,two single-point APD detectors are used to sample the two wavelengths separately.And the product is used as the performance evaluation function value of SPGD algorithm to achieve the effect of adjustable intensity of each wavelength component in the synthesized beam and separable steering angle.In the end,the experimental results are basically consistent with that of theory.