3D pseudospectral time domain for modeling second-harmonic generation in periodically poled lithium niobate ridge-type waveguides

Abstract

We report an application of the tri-dimensional pseudo-spectral time domain algorithm, that solves with accuracy the nonlinear Maxwell's equations, to predict second harmonic generation in lithium niobate ridge-type waveguides with high index contrast. Characteristics of the nonlinear process such as conversion efficiency as well as impact of the multimode character of the waveguide are investigated as a function of the waveguide geometry in uniformly and periodically poled medium.

High efficiency frequency doubling in fully diced LiNbO3ridge waveguides on silicon

“…The highest conversion efficiency is reached when two photons from the TM 00 pump mode combine to give a photon in the TM 00 SH mode thanks to an optimized mode overlap. Excitation of higher order modes can be minimized by carefully adjusting the size and the alignment of the injected beam [26]. Consequently, the energy of the guided beam mainly propagates in the fundamental mode which is favorable to obtain high conversion for frequency doubling.…”

Periodically poled LiNbO3ridge waveguides on silicon for second-harmonic generation

“…Indeed since the waveguide is multimode phase matching conditions can be fulfilled for different mode combinations as shown in ref [9]. Excitation of higher order modes can be minimized by carefully adjusting the size and the alignment of the injected beam [10]. Consequently, the energy of the guided beam mainly propagates in the fundamental mode which is favorable to obtain high conversion for frequency doubling.…”

Phase-matched second-harmonic generation in a flux grown KTP crystal ridge optical waveguide

“…The next step consists in using a precision dicing saw equipped with a 56-mmdiameter and 400-µm-thick diamond blades to define the ridges with low blade buckling in the hybrid stack [12]. Micrometric ridges with roughness sides of about 5 nm RMS are manufactured by adjusting the rotation speed and cutting speed of the dicing process to the material [15,16]. Because the KTP layer thickness is uneven when approaching the sample edge, the waveguides are cut transversely in the more uniform part to form 15.8-mm-long waveguides along the x-axis.…”

“…Ideally, square section waveguides are favored since it facilitates excitation of the waveguide fundamental mode. A good overlap is obtained if butt-coupling is realized with a Gaussian beam of proper dimension [16]. The effective indices of the guided modes have to be determined in order to accurately calculate the SHG BPM wavelengths and to properly design the corresponding waveguides.…”