Numerical Simulation On Mode Field Distribution In Near-stoichiometric Ti: LiNbO₃ Strip Waveguide Fabricated By VTE Technique

Through thoroughly analysis of the development trend and research evolvement,we aim to investigate the optical properties and technical parameters of the near-stoichiometric Ti:LiNbO₃ crystal,which is the hotspot recently, to realize the application in the integrated optical apparatus such as 1.55μm safe laser based on the theory and method of the waveguide optics.Along with the continuous complexity of the apparatus,it is impossible to solve such problems by using analytical method to get solutions to the Maxwell equations.Though sometimes we can get approximate solutions after simplization of a device,these solutions cannot provide enough theoretical support when we design and analyze those devices.But it is pratical to depict the electromagnetic problem using numerical and coding method.In practice,it makes sense to get the effective refractive index(ERI) and the mode field distribution in the LiNbO₃ crystal as an important waveguide material.Take the Ti:LiNbO₃ strip waveguide processed by the Ti indiffusion and vapour transport equilibration(VTE) simultaneously as the samples.We define the inner index curve by supposing the linearity between the Ti concentration and the induced index change together with SIMS measure results,and then adopt the ERI method to acquire the ERI value of the graded strip waveguide and the finite difference method to deal with the Helmholtz equation to describe the field distribution with proper boundary condition.By comparing the numerical values with the experimental results and the results simulated by the OPTIBPM software,it demonstrates good agreement with each other which proves our solution is reliable.The last section specifies the process of the Ti-indiffusion and VTE process.In realizing the algorithm,such works have been finished:a).the effective refractive index of the Ti:LiNbO₃ strip waveguide is settled using the ERI mehod;b).discretize the Helmholtz equation and the induced boundary condition adopting the finite difference method to get the explicit difference format,and ensure the second order precision for the solution.