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.