Design Of Optical Coupling System Of Vertical-Grown GaAs Optical Waveguide Phased Array

As a new type of optical phased array,Ga As optical waveguide phased array has the advantages of fast and radom-access beam scanning,low driving voltage,and easy integration,etc which has great application prospect both in military and civilian domain such as laser radar,laser guidance,and laser scanning imaging.However,current optical waveguide phased arrays have problems such as low utilization of light energy and unsatisfactory output beam quality.This paper mainly focuses on the theoretical and experimental research of semiconductor laser to vertical-grown optical waveguide array chip coupling.The main research results are obtained as follows:1 ? Theoretical and simulating analysis of the main factors of the coupling loss of the semiconductor laser-optical waveguide phased array chip is stuidied: Regardless of Fresnel reflection loss and misalignment loss,the coupling efficiency of laser diode to optic waveguide array chip is mainly caused by the spot size of the semiconductor laser beam and the mode field of the optical waveguide array chip.Mismatches cause serious loss of light energy.2?The influence of beam characteristics on the far-field distribution of the exit beam of the phased array chip is simulated and analyzed: 1)When the spot size of the laser beam is smaller than the mode field size of the optical waveguide phased array chip,the width of the main lobe of the far field distribution of the output beam will be widened,and the main lobe will also have a clear split.the spacing between the grating lobes and the main lobe becomes smaller,and there are many side lobes;2)The phase error introduced by the wavefront characteristics of the light beam causes the far field distribution of the output beam to have a certain burr on the main lobe and the grating lobe.The width of the main lobe widens and the scanning accuracy decreases.3?Theoretical analysis is studied that how divergence angle of the semiconductor laser influence the power-off deflection characteristics of the phased array.Under a given loading voltage,the divergence angle of the semiconductor laser in the direction of the slow axis causes different phase delays of the light entering the waveguide,affecting the far field distribution of the output beam,and failing to achieve accurate deflection of thescanning beam.4?Design and optimization of semiconductor laser-optical waveguide phased array chip coupling system is made:cylindrical and plane cylindrical lenses are used to collimate the fast and slow axis beams of semiconductor lasers respectively.The feasibility of the coupled system is verified by simulation and experiments.Experimental studies show that the beam is shaped using a fast-axis collimating lens.After the collimation,the half-divergence angle of the fast-axis beam is 2.04°,the coupling efficiency is increased from 5.4% to 28.7%,While improving the coupling efficiency,the output beam main-to-sidelobe ratio is 7.7d B,the mainlobe half-width is 2.1°,and the far-field beam quality is better.