Programmable Integrated Photonics with Phase-Change Materials

Phase-change materials (PCMs) have emerged as a promising platform for nonvolatile light modulation. The reversible switching between their stable amorphous and crystalline states leads to an impressive refractive index contrast (∆n, ∆k ~ 1–3). Integrated photonics has benefited from the progress of PCMs such as Sb2Se3 and Ge2Sb2Te5 for ultra-compact phase and amplitude modulators using all-optical and electro-thermal approaches. These devices allow small-form-factor silicon photonics with zero-static power yet reconfigurability, which are crucial properties in applications such as in-memory computing, optical synapses, switches, trimming, etc. Here, we review the various switching mechanisms and integration methods of PCMs in integrated photonic platforms.