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

We propose the design of a nonvolatile, low-loss optical phase shifter based on optical phase change material (O-PCM). The optical phase change material Ge₂Sb₂Se₄Te₁ (GSST), which exhibits low loss at telecommunication wavelength 1.55 μm as compared to other commonly used O-PCMs, is used in this work as the active material. Instead of direct interaction of the waveguide mode with the O-PCM, the design utilizes coupling between the primary SiN strip waveguide and a waveguide formed by O-PCM, in its amorphous state. The phase matching in the amorphous state inhibits the interaction of the waveguide mode with GSST in its highly 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) configuration using the designed phase shifter shows that the design can be used to obtain optical switching with a very small insertion loss and crosstalk over the entire C-band.