Record-low Loss Non-volatile Mid-infrared PCM Optical Phase Shifter based on Ge2Sb2Te3S2

We propose a low-loss non-volatile phase change material (PCM) phase shifter operating at mid-infrared wavelengths using Ge2Sb2Te3S2 (GSTS), a new selenium-free widegap PCM. The Si waveguide with GSTS exhibited the record-low optical loss for p phase shift of 0.29 dB/pi, more than 20 times better than the PCM phase shifters reported so far in terms of figure-of-merit, defined by Delta n/kappa(c), where Delta n and kappa(c) are the change in the refractive index and the extinction coefficient of the crystalline PCM, respectively. A GSTS phase shifter, enabled by our approach to use a wider bandgap PCM at a longer operating wavelength, is one of the solutions to realize a low-loss phase shifter for quantum photonic integrated circuits.