Design of a Compact Low-Loss Phase Shifter Based on Optical Phase Change Material

We propose the design of a nonvolatile,low-lossopticalphase shifter based on optical phase change material(O-PCM).The opticalphase change material Ge2Sb2Se4Te1(GSST), which exhibitslow lossat telecommunication wavelength1.55 μmas compared to other commonly used O-PCMs, is usedin this work as the active material. Instead of direct interaction of the waveguide mode with the O-PCM, the design utilizescouplingbetween the primary SiN strip waveguide andawaveguide formed by O-PCM, in itsamorphous state.Thephase matching in the amorphous state inhibits theinteraction of the waveguide mode withGSST in itshighly lossy crystalline state resulting in low loss operation.Due to a high differential refractive index between the two states of GSST, the design requires a very small length of the phase shifter to accumulate the desired phase difference.The overall response of the Mach-Zehnder Interferometer (MZI) configurationusing the designedphase shiftershows that the design can be used to obtain optical switching with avery small insertion loss and crosstalk over the entire C-band