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 ellipsometry, 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 considerably 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.