Low-loss silicon nitride photonic ICs for near-infrared wavelength bandwidth

Kirill A. Buzaverov, Aleksandr S. Baburin, Evgeny V. Sergeev, Sergey S. Avdeev, Evgeniy S. Lotkov, Mihail Andronik, Victoria E. Stukalova, Dmitry A. Baklykov, Ivan V. Dyakonov, Nikolay N. Skryabin, Mikhail Yu. Saygin, Sergey P. Kulik, Ilya A. Ryzhikov, and Ilya A. Rodionov

Optics Express, 31, 10, 16227-16242 (2023)

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 (220×550 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.