Reconfigurable slow light in phase change photonic crystal waveguide

Experimental demonstration of light propagation with ultralow group velocity, i.e., slow light, allows for revolutionary solutions for time-domain processing and buffering of optical signals. It can spatially compress optical energy, which lessens the device footprint and enhances linear and nonlinear optical effects. Photonic crystal waveguides (PCWs) are appealing for producing slow light since they can be on-chip integrated and operated under room temperature. However, most PCW slow-light devices are restricted to the narrow spectral range of material resonance, leading to a small delay-bandwidth product, which restricts the maximum data rate, operation frequency, and storage capacity. Furthermore, the lack of broadly tunable slow light hinders practical applications in tunable photonic devices. We propose a reconfigurable slow-light device using a PCW based on a prototypical chalcogenide glass, Ge₂Sb₂Te₅ (GST225) to solve the problems. We find that the operating wavelength of the slow light within the structure can be reversibly switched between 3575 and 4905 nm by changing the structural state of GST225 between amorphous and crystalline ones. The corresponding average group indices are 40.8 and 54.4, respectively. We experimentally illustrate that the reversible phase transition of GST225 between amorphous and crystalline ones can be realized in nanoseconds. Our proof of concept may provide a platform for actively engineering slow light that might otherwise be difficult to obtain in photonic systems. We expect it to improve the device performance in the fields of nonlinearity and sensing.