A heterogeneously integrated lithium niobate-on-silicon nitride photonic platform

Abstract

Lithium niobate (LiNbO3) remains the most common χ2-material for electro-optic devices due to its physical properties and commercial availability [1]. With the development of thin-film lithium niobate-on-insulator (LNOI) the material started to be used for photonic integrated circuits with ultimate performance in respect to the conventional bulk lithium niobate photonics [2-4]. However, modern integrated lithium niobate photonic solutions lack some of the features routinely achieved in other platforms such as silicon or silicon nitride [5]. We present our recent advances in heterogeneously integrated lithium niobate photonics, combining thin-film LNOI with the photonic Damascene silicon nitride technology [6]. The platform retains low optical propagation losses (<0.1 dB/cm) as well as fiber-to-chip insertion losses (<2.5 dB/facet) of the underlying silicon nitride waveguides. The lithographic precision of the underlying silicon nitride waveguides fabrication helps to achieve 3-dB splitters/couplers with <1 dB insertion loss using silicon nitride inverse tapers.