Ultrafast broadband tuning of resonant optical nanostructures using phase change materials

The functionalities of a wide range of optical and opto-electronic devices are based on resonance effects and active tuning of the amplitude and wavelength response is often essential. Plasmonic nanostructures are an efficient way to create optical resonances, a prominent example is the extraordinary optical transmission (EOT) through arrays of nanoholes patterned in a metallic film. Tuning of resonances by heating, applying electrical or optical signals has proven to be more elusive, due to the lack of materials that can induce modulation over a broad spectral range and/or at high speeds. Here we show that nanopatterned metals combined with phase change materials (PCMs) can overcome this limitation due to the large change in optical constants which can be induced thermally or on an ultrafast timescale. We demonstrate resonance wavelength shifts as large as 385 nm - an order of magnitude higher than previously reported - by combining properly designed Au EOT nanostructures with Ge2Sb2Te5 (GST). Moreover, we show, through pump probe measurements, repeatable and reversible, large amplitude modulations in the resonances, especially at telecommunication wavelengths, over ps time scales and at powers far below those needed to produce a permanent phase transition. Our findings open a pathway to the design of hybrid metal PCM nanostructures with ultrafast and widely tuneable resonance responses, which hold potential impact on active nanophotonic devices such as tuneable optical filters, smart windows, biosensors and reconfigurable memories.