Switchable Induced-Transmission Filters Enabled by Vanadium Dioxide

An induced-transmission filter (ITF) uses an ultrathin metallic layer positioned at an electric-field node within a dielectric thin-film bandpass filter to select one transmission band while suppressing other bands that would have been present without the metal layer. We introduce a switchable mid-infrared ITF where the metal can be "switched on and off", enabling the modulation of the filter response from a single band to multiband. The switching is enabled by the reversible insulator-to-metal phase transition of a subwavelength film of vanadium dioxide (VO₂). Our work generalizes the ITF─a niche type of bandpass filter─into a new class of tunable devices. Furthermore, our fabrication process─which begins with thin-film VO₂ on a suspended membrane─enables the integration of VO₂ into any thin-film assembly that is compatible with physical vapor deposition processes and is thus a new platform for realizing tunable thin-film filters.