Fabrication And Characterization Of Buffered Proton Exchange Near-stoichiometric LiNbO₃ Optical Waveguides

LiNbO₃(LN)crystal has excellent electro-optical,piezoelectric and nonlinear optical properties,and low transmission loss in visible and near-infrared bands.Compared with congruent lithium niobate(CLN)crystal,near-stoichiometry lithium niobate(NSLN)shows stronger electro-optical and nonlinear effects and lower domain reversal polarization voltage than congruent lithium niobate crystal.Therefore,in this paper,the diffusion coefficients of NSLN under different conditions were studied in detail for the first time by proton exchange method,and two diffusion mechanisms were established.Secondly,the corrosion characteristics of crystals after proton exchange were qualitatively analyzed.Finally,the NSLN strip waveguide was prepared and characterized by buffered proton exchange and annealing.This work opens up a new path for making high quality PPLN waveguide.This paper mainly studies and discusses the following aspects:1.Z-cut CLN crystal is used as the initial material.Use VTE technique was used to prepare the NSLN crystals,CLN crystal and NSLN crystals will be herculean task in different concentration(0%?3%)in the exchange of melt at different temperature(210?,225?,245?),proton exchange,then some samples at different temperature(300?,360?,376?)annealing,made a series of planar optical waveguide,using prism coupling instrument measuring and IWKB method fitting the corresponding waveguide refractive index profile,diffusion coefficient to calculate the exchange and annealing.2.The diffusion coefficients of NSLN crystal and CLN crystal were analyzed.The results show that the annealing diffusion coefficient in CLN crystal is always larger than that in NSLN crystal,and the exchange diffusion coefficient in the two materials depends on the concentration of exchange melt and exchange temperature.By comparing the size relationship between exchange and annealing diffusion coefficient in NSLN crystal and CLN crystal,two diffusion mechanisms are concluded:exchange diffusion mechanism and annealing diffusion mechanism.The proton exchange process is the result of the joint action of these two diffusion mechanisms.After proton exchange,the crystal was put into the mixed acid for corrosion at different times(0?600 min),and corrosion characteristics were obtained,so as to determine the appropriate exchange solution concentration,exchange temperature and time,annealing temperature and time to make the NSLN strip optical waveguide.3.Z-cut CLN and NSLN crystals are used as initial materials.The silica mask was made by magnetron sputtering in the material+Z surface photolithography,and then the 2.5%buffer was used to exchange protons for 60 h at 225?,and then annealed at 320?for 20 h to obtain the 8 microns wide waveguide.Firstly,Rsoft software was used to simulate the near-field mode of the waveguide at 1550 nm wavelength.Secondly,a near-field mode acquisition system was built to collect the near-field modes of CLN and NSLN waveguides.It was found that the profile of the mode field along the width direction met the gaussian profile,and the profile of the mode field along the depth direction met the hermitic gaussian profile,which was consistent with the simulation results.Finally under the waveguide length of 1.2 cm,calculate the herculean task and NSLN waveguide insertion loss of 2.4 d B and 2.9 d B respectively,coupling loss of 0.39 d B and 0.41 d B respectively,it is concluded that herculean task and NSLN waveguide transmission loss were 0.85 d B/cm and 1.23d B/cm,and using the truncation method tests for the two materials of transmission loss is calculated,the article draw a herculean task and NSLN waveguide transmission loss were 0.75 d B/cm and 1.25 d B/cm.