Preparation And Characteristic Of Li-poor Ti In-diffused Linbo₃ Planer Waveguide

With the rapid development of optical communications, integrated optical deviceswhich are used to build all-optical network have become the research focus. Andwaveguide device, especial planar optical waveguide is the important part of manyintegrated optical devices .Currently, the most common planar waveguide is titaniumin-diffusion lithium niobate planar waveguide, and many reports about it, but thosestudies undertaken most are based on congruent or near stoichiometric titaniumin-diffusion lithium niobate waveguides, the Li-poor titanium in-diffusion lithiumniobate waveguides are few reported. This dissertation characterizes the Li-poor Tiin-diffusion lithium niobate waveguides, and obtained some preliminary results, laidthe foundation for further study.The main work of this dissertation include the following aspects:1. Prepared Li-poor crucible: prepared Li₂CO₃and Nb₂O₅by the molar ratio of 4:6, andmixed. The mixed powder was placed in the crucible mold and pressed into shape.Then calcined 10 hours under 1000°C , and calcined 1 hour under 1100°C . So aLi-poor two-phase ( LiNbO₃ + LiNb₃O₈) crucible was prepared.2. Li-poor VTE treated: series 1-mm-thick Z-cut congruent LiNbO₃ plates wereLi-poor VTE treated by the prepared Li-poor two-phase crucible. The VTE treatmentwas carried out fixed at 1100°C for different durations ranging from 100 to 180hours.Then measured the surface birefringence and calculated the lithium componentof each plate.3. Diffusion: deposited Ti film on the LiNbO₃ plates firstly, and the Ti film thicknessrange is (110-135)±5 nm.Then put the plates into the diffusion furnace to prepareLi-poor titanium in-diffusion LiNbO₃ planar waveguides. And the diffusiontemperature is fixed at the 1050°C , the diffusion time range from 8 to15 hours. In themeantime, in order to suppress Li out-diffusion , we accessed wet oxygen to thediffusion furnace at the rate of 1 L /minduring the diffusion process.4.Characterized: prism coupling technique used to measure the effective refractiveindexs of everal guided modes of planar waveguide, then got the corresponding refractive index distribution inversely by software. Fitted the distributionsrespectively by Gaussian model, and confirmed that the refractive index distributionof Li-poor LiNbO3 Ti in-diffusion planar waveguide is fitted Gaussian model,whichwas the same as congruent LiNbO3 Ti in-diffusion planar waveguide.Analysised therelationship between the change of the surface refractive index and the ratio of initialthickness of Ti film and diffusion deepth.,and got that the diffusion coefficient wouldincreased while the Li component declined.While the Li component declined from48.6mol% to 48.0mol% and 47.mol%, the diffusion coefficient increased from2.367×10^-12cm²/sec to 3.424×10^-12cm²/sec and 5.281×10^-12cm²/sec。Finally,calculated the refractive indices of waveguide by using Gaussian distribution model,and calculated the number of modes should appeared in waveguide according thechange value of the surface. Found that the error between the calculated and measuredeffective refractive index were inside 0.00006 and the number of modes consistentwith the calculated results. This fully shows that the accuracy of the measurement.