Study On The Acoustic-optical Waveguide Modulators Of Surface Acoustic Wave Type

With the development of surface acoustic wave technology and integrated optical technology,people have paid more and more attention to the acousto-optic waveguide modulators of surface acoustic wave type manufactured by using the principle of acousto-optic interaction.As the acousto-optic waveguide devices driven by surface acoustic wave has the advantages of easy integration,small size,low driving power,and large bandwidth,it has good application prospects in Q-switched lasers,optical signal processing,laser display,and optical communications.As a type of acousto-optic device,acousto-optic waveguide modulators of surface acoustic wave type can be used to modulate the frequency,amplitude,and direction of incident guided light waves outside the laser cavity,it also can be used as an acousto-optic Q switch inside the laser cavity which makes the laser produce pulse output with a high peak power.In this paper,we research and design the acousto-optic waveguide modulators of surface acoustic wave type systematically based on LiNbO3 crystals.Finally,two finished devices are made,and their performances are tested.It is proved that the device occurs the acousto-optic Bragg diffraction.The main work of this paper is as follows:1.Firstly,we select LiNbO3 crystal as the substrate of the waveguide-type acousto-optic modulator.Secondly,we start with the Christoffel equation of the surface acoustic wave and then draw some more valuable conclusions by analyzing the transmission characteristics of the coupled waves in different tangent and propagation directions of the LiNbO3 crystal and the distribution characteristics of the field components of the coupled waves.Finally,a method for solving the linear weighting coefficients of coupled waves is proposed in this paper for the first time.2.The acousto-optic interaction characteristics which based on the 128°YX-LiNbO3 acousto-optic waveguide device are systematically studied,and the superposition integration factor,superposition integration,and acoustic power P100 of the guided light wave in different modes are calculated and discussed.It is theoretically found that the optimal driving acoustic power at a driving frequency of 200 MHz with the thickness of 3?m in the TM mode is 1.05 W.We also simulate and analyze the effects of waveguide depth,length of acousto-optic zone,and driving power on diffraction efficiency.3.We first design the parameters of the interdigital transducer using interference theory,and then use the finite element analysis software COMSOL to perform multiphysics modeling and simulation on the surface acoustic wave device.We perform harmonic response analysis and modal analysis on the designed device to accurately simulate the resonance frequency,surface acoustic wave mode,potential and stress distribution,and simulation analysis of the mass loading effect of different materials.Finally,a single-port interdigital transducer with a resonance frequency of 192.0MHz is designed.4.The effective refractive index method is used to solve the effective refractive index of the Ti-diffused optical waveguide,and the preliminary design of the width and depth of the optical waveguide is obtained based on the derivation and simulation of the waveguide mode characteristic equation.5.We use OptiBPM software which based on the beam propagation method theory to design,analyze and optimize the optical waveguide pattern,and also analyze the effects of acousto-optic effect on the length of the acousto-optic action area in 1000?m and 2000?m.Finally,the theoretically optimal design scheme is given by simulation results.6.We semi-package and impedance-match the two chips that are fabricated and measure their driving frequencies are 203MHz and 189.5MHz respectively.We also theoretically analyze the generation of body waves and surface acoustic standing waves,and experimentally suppress their output well.We design experiments to test the diffraction efficiency of the device,which proves that the theoretical design is feasible.Finally,the experimental deficiencies are summarized more comprehensively and the measures that can be improved are put forward.