The Structural Design And Theoretical Investigation Of Periodically Poled LiNbO₃Waveguides

LiNbO3offers excellent electro-optic, acousto-optic, and nonlinear optical proper-ties. Therefore, LiNbO3waveguides can be used to prepare various optical devices, in-cluding electro-optical modulators, tunable filters, amplifiers and (tunable) lasers ofdifferent types, and nonlinear wavelength converters. In particular, periodically poledLiNbO3(PPLN) waveguides are ideal candidates for extremely efficient nonlinear opt-ical devices for wavelength conversion and all-optical signal processing.(1)The advantages and disadvantages of various preparation processes for LiNbO3waveguides are presented. Our study shows that the preparation processes of directbonded LiNbO3waveguide are very simple, easy to be implemented and controlled.Through this preparation processes, we can get a kind of optical waveguides with steprefractive index distribution and with a strong limit for the light field. Now we willstudy the structural design of the direct bonded ridge waveguide in this paper becauseonly a few case reports about its structural design and characteristics of mode field.(2) We put forward that we can use the finite difference method for the directbonded of the rib waveguide numerical simulation. The doped LiNbO3materials werestudied to improve the LiNbO3anti-photorefractive properties. According to the finitedifference method, we design the program to obtain the optical waveguide mode fielddistribution and effective refractive index and other parameters, according to these pa-rameters, the structure dimensions of the waveguide are designed and optimized.(3)We introduce the concept of the modal overlap factor and the definition of thetype for the modal overlap factor. The relationship between the modal overlap factorand the structure of the waveguide was obtained by numerical simulation. The modaloverlap factor was put into the coupled wave equations, and the equations was corrected,which can be used to design waveguide dimensions in order to achieve maximum wa-velength conversion efficiency, also we proposes a program of using the linearly chirped periodic structure to broaden the bandwidth of the PPLN pump, and have a nu-merical simulation for it.(4) We propose introducing one-dimensional photonic crystal into the periodic po-larization reversal LiNbO3waveguides. According to the requirement, we design thestructure of one-dimensional photonic crystal, to get the right reflection spectrum,making the optical wavelength of the signal light and pump light in the photonic bandgap in order to reduce transmission loss, then we use the finite difference method to si-mulate the new optical waveguide, and find that the novel structure of optical wave-guides have high conversion efficiency while low transmission loss.(5) We propose a program of achieving UWB pulse based on PPLN waveguides.We numerically simulate the process of putting the Gaussian pulse into the PPLN wa-veguide to generate UWB pulse, and demonstrate the feasibility of the program, andoptimize the pulse width, the delay volume and other parameters.