Fabrication And Performance Of Thin Film Optical Waveguide Acoustooptic Modulator

The thin film acoustooptic modulator based on lithium niobate film has the advantages of low power consumption,good stability,high extinction ratio,small size,high modulation efficiency and easy integration.In this paper,a series of experimental research and theoretical analysis are carried out for the lithium niobate thin film optical waveguide acoustoptic mod-ulator.The research results are of high practical value and have a good guiding significance for the development of acoustoptic modulator.Since MZ structure optical waveguide has lower additional loss and higher coupling efficiency,this paper chooses MZ optical waveguide as the main research object,and the main work includes:I.An electrode structure and an MZ optical waveguide structure are designed,and the simulation results are as follows:1)The widths of the waveguides are 5.3μm,5.15μm,5.0μm,the angles of the waveguides areθ₁=0.0573°andθ₂=0.0564°,and the lengths of the acous-tooptic interaction zones are 1.8cm and 2.3cm,respectively.2)the cross finger width of the cross finger transducer is 6.75μm,the length of the cross finger is 1.8cm,the cycle is 27μm,the electrode thickness is 100nm,and the electrode logarithm is 8.3)The traveling-wave electrode electrode spacing is 11.5μm,the width is 7μm,the silicon dioxide thickness is1.2μm.In this paper,the working frequency of acoustooptic modulator can be changed ac-cording to the frequency of rf signal,which increases the flexibility of the device.II.The fabrication of thin-film optical waveguide acoustooptic modulator is carried out:1)the buffered proton exchange,the core technology of optical waveguide fabrication,is studied.The exchange conditions are determined as follows:the concentration of exchange solution is 3%,the exchange temperature is 245℃,the exchange time is 5h,the annealing temperature is 370℃,and the annealing time is 3h and 30min;2)In this experiment,X-cut lithium niobate film is selected as the initial material to complete the overall fabrication of thin-film optical waveguide acousto-optic modulator.In this paper,the insertion loss of acoustooptic modulator is effectively reduced by studying the selection of initial materials and exchange conditions.III.Test the performance of thin film optical waveguide acousto-optic modulator:1)test the insertion loss of thin film optical waveguide acousto-optic modulator,and the minimum loss is 3.5d B,which meets the loss requirements of acousto-optic modulator;2)In the near-field mode,the influence of the mode field on the insertion loss is analyzed,and through the judgment of the light intensity of the two arms of the optical waveguide,it is concluded that the thin-film optical waveguide acousto-optic modulator has high modulation efficiency;3)The test system of thin film optical waveguide acoustooptic modulator is designed and built,the diffraction efficiency is tested,and the results are analyzed.In this paper,the design of thin-film optical waveguide acousto-optic modulator is com-pleted,and the acousto-optic modulator is successfully fabricated on X-cut lithium niobate film.After testing and comparative analysis,the results show that the modulator made of thin-film material has great advantages in loss and modulation efficiency compared with bulk material.The work of this paper lays a foundation for the follow-up research of thin film acoustooptic modulator.