Phase change material-based silicon-on-sapphire waveguides: a comparative study for nonvolatile optical switching

Phase change materials (PCMs) offer remarkable tunability of optical properties, making them promising candidates for reconfigurable photonic devices. In this work, we design and compare programmable optical ON-OFF switches based on silicon-on-sapphire (SOS) ridge waveguides integrated with a thin PCM film. Four different PCMs, such as GST, GSST, Sb₂S₃, and Sb₂Se₃ are investigated at the telecommunication wavelength of 1.55 𝜇m. Material studies reveal that Sb₂S₃exhibits the lowest optical absorption in the C-band, while GST shows stronger refractive index contrast. A finitedifference time-domain (FDTD) simulation is employed to study the impact of phase change materials and their thicknesses on the optical response of the hybrid waveguides. We evaluate device performance using two key metrics: electro-refraction (ER), which quantifies the phase tunability, and electro-absorption (EA), which reflects the insertion loss. Our results indicate that GST provides the highest ER values, enabling compact switching functionality, though it suffers from relatively higher losses. In contrast, Sb₂S₃ shows minimal loss but with reduced ER, suggesting a trade-off between compactness and efficiency. In particular, GST-based SOS waveguides are identified as strong candidates for compact ON-OFF switching, while Sb₂S₃ may be preferred where ultra-low loss is critical. Building on these preliminary results, we outline a pathway toward high-performance Mach-Zehnder interferometer (MZI) optical switches with applications in reconfigurable photonic circuits, optical interconnects, and emerging computing architectures.