Hybrid Silica and Thin-Film Lithium Niobate Waveguides and Y-Junctions

Abstract

Silica (SiO2) strip-loaded waveguides and Y-junctions on lithium niobate (LN) thin film were designed, fabricated and experimentally investigated. We studied the optical power distribution in strip-loaded waveguides firstly. Simulations showed that most of the power (more than 82%) was confined in the LN layer, and the dimensions of SiO2 loading strip had little influence on optical power distribution. The SiO2 film was deposited by the magnetron sputtering method. The deposited SiO2 layer approached stoichiometric SiO2, and a smooth surface was obtained. A group of waveguides with widths of 2‒5 μm were fabricated using lift-off technology. The 2 μm-wide waveguide displayed low propagation losses of 0.2 dB/cm for the quasi-TE (q-TE) mode and 0.8 dB/cm for the quasi-TM (q-TM) mode at the wavelength of 1550 nm. Based on the low loss waveguides, Y-junctions with small sizes were designed and fabricated. The transmission could reach 70% -80%, and the splitting ratio maintained at a stable level around 1:1. The low-loss strip-loaded waveguides and Y-junctions offer the possibility of combining SiO2 and LN materials for integrated optics. More high-performance photonic devices and circuits using this method are expected in the future.

Keywords: Lithium niobate thin film, waveguides, Silica