Layered Gallium Monosulfide as Phase-Change Material forReconfigurable Nanophotonic Components On-Chip

he demand for information processing at ultrahigh speed with large datatransmission capacity is continuously rising. Necessary building blocks foron-chip photonic integrated circuits (PICs) are reconfigurable integratedlow-loss high-speed modulators and switches. Phase change materials(PCMs) provide unique opportunities for integration into PICs. Here, theinvestigation of layered gallium monosulfide (GaS) as a novel low-loss PCMfrom infrared to optical frequencies is pioneered, with high index contrast (��n≈0.5) at the optical telecommunication band. The GaS bandgap switchesfrom 1.5±0.2 eV for the amorphous state to 2.1±0.1 eV for the crystallinestate. It is demonstrated that the reversible GaS amorphous-to-crystallinephase transition can be operated thermally and by picosecond green (532 nm)laser irradiation. The design of a reconfigurable integrated optical modulatoron-chip based on Mach-Zehnder Interferometers (MZI) with the GaS PCM celldeposited on one of the arms for application is presented at thetelecommunication wavelength of��=1310 nm, where the standard singlemode optical fiber exhibits zero chromatic dispersion, and at��=1550 nm,where a minimum optical loss of 0.22 dB km−1is obtained. This opens theroute to applications such as reconfigurable modulators, beam steering usingphase modulation, and photonic neural networks.