Edge coupling for hybrid mono-crystalline silicon and lithium niobate thin films

Abstract

The hybridization of mono-crystalline silicon and lithium niobate thin films (Si-LNOI) combines the excellent electrical properties and mature micro-nano processing technology of Si, as well as the remarkable optical properties of LN. The Si-LNOI platform will drive new and promising integrated photonics devices. High-efficiency fiber-waveguide optical coupling is necessary to realize the full potential of devices and practical applications. In this study, a spot-size converter (SSC) was designed and demonstrated for efficient edge coupling between a Si-LNOI waveguide and lens fiber. The SSC was fabricated by standard semiconductor process, which consisted of an inverted-tapered Si and a silicon-rich nitride (SRN) waveguide overlying the inverted-tapered Si. At a wavelength of 1550 nm, the TE and TM light achieved coupling losses of 1.9 and 2.1 dB/facet, respectively. The coupling efficiency was stable in the wavelength range of 1500–1600 nm. The tolerance of alignment was also evaluated.