Record-low Loss Non-volatile Mid-infrared PCM Optical Phase Shifter based on Ge2 Sb2 Te3 S2

We propose a low-loss non-volatile phase change material (PCM) phase shifter operating at mid-infrared wavelengths using Ge 2 Sb 2 Te 3 S 2 (GSTS), a new selenium-free widegap PCM. The Si waveguide with GSTS exhibited the record-low optical loss for $\pi$ phase shift of $0.29\text{dB}/\pi$, 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 $\kappa_{\text{c}}$ 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.