Modal analysis of arbitrary-oriented ridge waveguides in x-cut lithium niobate thin film

Abstract

Abstract We theoretically and numerically investigate the mode properties of ridge waveguides made on lithium niobate (LN) subwavelength thin film by taking into complete account the anisotropic feature of LN crystal. We analyze the effective refractive index of the quasi-transverse-electrical (q-TE) and quasi-transverse-magnetic (q-TM) modes and their difference in arbitrary-oriented waveguides on x-cut lithium niobate on insulator. Waveguide simulations based on full-vectorial finite element method are performed. The geometrical parameters and directions of the optical axis of the LN material for the ridge waveguides are varied to investigate the single-mode condition, optical power distribution and mode hybridization effect in the straight waveguides. The different trends in optical power distribution in LNOI waveguide between q-TE and q-TM at different crystal optical axis angles will be explained in detail.