Switchable induced-transmission filters enabled by vanadium dioxide

TL;DR

This paper presents a switchable mid-infrared induced-transmission filter using vanadium dioxide that can toggle between broad and narrow passbands, enabling tunable filter responses for infrared applications.

Contribution

The work introduces a reversible VO2-based switchable ITF that can dynamically change its transmission band, expanding the functionality of thin-film filters.

Findings

Successfully demonstrated switching between broad and narrow passbands in LWIR

Developed a fabrication process compatible with standard PVD techniques

Enabled integration of VO2 into various thin-film filter architectures

Abstract

Abstract: An induced-transmission filter (ITF) uses an ultrathin layer of metal positioned at an electric-field node within a dielectric thin-film bandpass filter to select one transmission band while suppressing other transmission bands that would have been present without the metal layer. Here, we introduce a switchable mid-infrared ITF where the metal film can be "switched on and off", enabling the modulation of the filter response from single-band to multiband. The switching is enabled by a deeply subwavelength film of vanadium dioxide (VO2), which undergoes a reversible insulator-to-metal phase transition. We designed and experimentally demonstrated an ITF that can switch between two states: one broad passband across the long-wave infrared (LWIR, 8 - 12 um) and one narrow passband at ~8.8 um. Our work generalizes the ITF -- previously a niche type of bandpass filter -- into a new class of tunable devices. Furthermore, our unique 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 (PVD) processes, and is thus a new platform for realizing tunable thin-film filters.