Low-loss silicon nitride photonic ICs for single-photon applications

TL;DR

This paper reports the development of ultra-low-loss silicon nitride photonic integrated circuits optimized for single-photon applications, achieving record low propagation losses at near-infrared wavelengths.

Contribution

It introduces a labs-scale process for fabricating low-loss silicon nitride PICs with record low propagation losses suitable for quantum photonics.

Findings

Achieved propagation losses as low as 0.55 dB/cm at 925 nm.

Used advanced e-beam lithography and plasma etching for smooth waveguide sidewalls.

Provided a platform for further improvements with additional fabrication techniques.

Abstract

Low-loss photonic integrated circuits (PICs) are the key elements in future quantum technologies, nonlinear photonics and neural networks. The low-loss photonic circuits technology targeting C-band application is well established across multi-project wafer (MPW) fabs, whereas near-infrared (NIR) PICs suitable for the state-of-the-art single-photon sources are still underdeveloped. Here, we report the labs-scale process optimization and optical characterization of low-loss tunable photonic integrated circuits for single-photon applications. We demonstrate the lowest propagation losses to the date (as low as 0.55 dB/cm at 925 nm wavelength) in single-mode silicon nitride submicron waveguides (220x550 nm). This performance is achieved due to advanced e-beam lithography and inductively coupled plasma reactive ion etching steps which yields waveguides vertical sidewalls with down to 0.85 nm sidewall roughness. These results provide a chip-scale low-loss PIC platform that could be even further improved with high quality SiO2 cladding, chemical-mechanical polishing and multistep annealing for extra-strict single-photon applications.