Proposal of Low-Loss Non-Volatile Mid-Infrared Optical Phase Shifter Based on Ge2Sb2Te3S2

An optical phase shifter based on phase-change materials (PCMs) is a promising building block of quantum photonic integrated circuits (QPICs) operating at mid-infrared (MIR) wavelengths on a Si photonics platform. In this article, we propose a record low-loss non-volatile PCM phase shifter operating at MIR wavelengths based on Ge2Sb2Te3S2 (GSTS), which is a new Se-free widegap PCM. On the basis of the refractive index and extinction coefficient spectra measured by spectroscopic ellipsome-try, we show that GSTS has excellent material properties for optical phase shifters. By using GSTS in the MIR range, the optical absorption of a PCM phase shifter can be consider-ably reduced. We achieved an optical loss of 0.29 dB for a pi phase shift, which is the lowest loss ever reported for a PCM phase shifter integrated with a Si waveguide. We also demonstrate the non-volatile resonance wavelength tuning of a microring resonator (MRR) with a GSTS phase shifter and the optically induced phase transition of a GSTS phase shifter based on laser irradiation.