A fundamental mode converter based on tapered LiNbO3-on-insulator photonic wire with a laterally asymmetric structure

Abstract

We report a mode converter based on a tapered X-cut/Y-propagation ridge-type LiNbO 3 -on-Insulator (LNOI) photonic wire (PW) with a laterally asymmetric refractive index profile realized by introducing a semi-infinite dielectric cover layer on one side of the LNOI PW. The interplay of material and waveguide birefringence enables to realize mode hybridization, which is a prerequisite for realizing mode conversion. The introduction of the semi-infinite cover layer and the use of a taper structure modify mode index and electric field distribution, enabling to realize mode conversion. Aiming at 1.55 μm wavelength, we have simulated mode hybridization and conversion characteristics of the tapered, laterally asymmetric ridge-type LNOI PW. The results show that a conversion between fundamental TM 00 and TE 00 modes can be realized. The conversion efficiency can be optimized by choosing an appropriate cover layer material and/or adjusting its thickness. An ultra-compact device with a taper length <100 μm is expected. • A mode converter based on a tapered LNOI photonic wire (PW) is proposed. • The device has a laterally asymmetric refractive index profile. • Asymmetric index profile and taper structure enable to realize mode conversion. • A conversion between fundamental TM 00 and TE 00 modes is realized. • An ultra-compact device with a taper length <100 μm is expected.