A New Family of Ultralow Loss Reversible Phase‐Change Materials for Photonic Integrated Circuits: Sb2S3 and Sb2Se3

Phase-change materials (PCMs) are seeing tremendous interest for their use in reconfigurable photonic devices; however, the most common PCMs exhibit a large absorption loss in one or both states. Here, Sb(2)S(3)and Sb(2)Se(3)are demonstrated as a class of low loss, reversible alternatives to the standard commercially available chalcogenide PCMs. A contrast of refractive index of Delta n = 0.60 for Sb(2)S(3)and Delta n = 0.77 for Sb(2)Se(3)is reported, while maintaining very low losses (k < 10(-5)) in the telecommunications C-band at 1550 nm. With a stronger absorption in the visible spectrum, Sb(2)Se(3)allows for reversible optical switching using conventional visible wavelength lasers. Here, a stable switching endurance of better than 4000 cycles is demonstrated. To deal with the essentially zero intrinsic absorption losses, a new figure of merit (FOM) is introduced taking into account the measured waveguide losses when integrating these materials onto a standard silicon photonics platform. The FOM of 29 rad phase shift per dB of loss for Sb(2)Se(3)outperforms Ge(2)Sb(2)Te(5)by two orders of magnitude and paves the way for on-chip programmable phase control. These truly low-loss switchable materials open up new directions in programmable integrated photonic circuits, switchable metasurfaces, and nanophotonic devices.