Optimizing And Realizing Electro-optic Deflection Of Lithium Niobate Waveguide With Microstructure Electrode

High-speed beam deflection devices are widely used in various fields,such as high-speed optical switch,phased array microwave radar scanning,beam smoothing and so on.At present,there are some problems in beam deflector,such as large driving voltage,large device size and difficult for high-speed deflection.Lithium niobate is an electro-optic material,which has advantages of high electro-optic coefficient of 30.8 pm/V,low transmission loss of 0.2 dB/cm,improved fabrication technology and easy integration.The electro-optic modulation of speed of mode field depends on the response speed of the electro-optic material.In this paper,the electro-optic deflection of lithium niobate waveguide with microstructured electrodes is studied.In the direction of beam propagation,the core of the waveguide will form an array of refractive index prisms due to the electro-optic effect,and the deflection of the optical field in the lithium niobate waveguide can be modulated by the applied voltage of the electrodes through the applied driving voltage to the isosceles sawtooth electrode above the annealed proton(APE)lithium niobate waveguide.The design of deflection scheme based on lithium niobate waveguide is introduced.The waveguide mode deflection is simulated.Then the waveguide mode deflection is experimentally studied.The horizontal divergence angle of the waveguide output beam passing through the objective lens and the response of waveguide scattering(S21)parameters are measured.Firstly,theoretical analysis is performed and COMSOL Multiphysics is used to verify the electric filed enhancement of the micro-structure electrodes.Then RSoft software is used to simulate the waveguide electro-optic deflection and optimize the waveguide width and the electrode structure.For 1064 nm light source,the voltage is applied to the sawtooth electrode.The slope of the linear fitting curve of the optical field mode transverse deflection at the output side of the APE waveguide with the width of 80?m are 1.9 times and 20 times larger than that of the APE waveguides with the width of 30?m and 15?m,respectively.For the waveguide with a width of80?m,A maximum transverse deflection of~15.6?m is obtained for isosceles triangle electrodes under 50 V,which is much larger than the maximum transverse deflection of the rectangular triangle electrode(~7.72?m).The slope of the linear fitting curve of the light field mode transverse deflection at the waveguide output side with the isosceles triangle is 2.5 times larger than that of the right triangle.In the wavelength range 1004-1024 nm under±20 V,0 V,the deviations of output mode deflection are smaller than 0.086?m/V,indicating its good stability in this wavelength range.The results of waveguide electro-optic deflection experiment are consistent with those of RSoft simulation.For 1064 nm light source,the position of optical field mode on the output surface of 15?m and 30?m waveguides is almost unchanged.The APE lithium niobate waveguide electrode with 80?m width is applied with DC voltage(±50 V,±40 V,±30 V,±20 V,±10 V,0 V)for static modulation.The maximum transverse deflection of optical field mode on the output surface are~15.13?m and~15.6?m for experimental and simulated results,respectively.The experimental results and simulation results are presented with mode deflectionof 0.265?m/V and0.267?m/V,respectively,which have a difference of 1.02%.When the AC voltage is 18 V and the frequency is 50 Hz,the peak intensity of the mode decreased by 30%,and the half-width of the Gauss distribution is broadened by 2 times.For 980 nm light source,the mode deflections of the experimental and simulation results are 0.24?m/V and 0.29?m/V,respectively.The horizontal divergence angle of the waveguide output beam through the 20X objective is5.981 mrad measured by M~2 instrument.Measuring the horizontal divergence angle of the waveguide output beam through the 20X objective lens by a mobile CMOS camera is 1.09 mrad.By measuring the S21 parameters of waveguide devices,resonance is generated at relatively low frequency output(1.25 GHz),but the overall-3 dB bandwidth can reach 3.4 GHz.The innovations of this paper are as follows:1.APE lithium niobate waveguide has a horn-shaped input structure,which can effectively reduce the side lobe of the spot.The output mode field is a composite mode with the fundamental mode as the main component.2.The structure of the electrode is isosceles triangle.Under the electro-optic effect,the transverse deflection of the optical field mode on the output side of the waveguide can be increased and the driving voltage can be reduced.3.The broad bandwidth of 980-1064 nm is realized.