Thin layers of vanadium dioxide as electrical modulators of the optical signal amplitude

Phase change materials (PCMs), which undergo a phase transition in response to external stimuli such as, for example, heat or light, allow construction of active nanophotonic devices. Vanadium dioxide (VO₂) is PCM which experiences an isolator-metal phase transition when heated from room to elevated temperature. The phase change of VO₂ occurs at approximately 68 °C and results in substantial refractive index change, thus allows for simple, low power, near room temperature light modulation. VO₂ modulators have significant advantages compared to other modulating techniques, such as operation in a broad spectral range from near-infrared to terahertz, non-binary signal changes, and low trigger pulse power. The highest recently reported modulation frequency is of the order of several tens of kHz. We demonstrate a broadband optical modulator based on vanadium oxide. The modulator is composed of a glass substrate on which a layer of VO₂, a transparent indium tin oxide (ITO) layer, and gold electrodes were deposited. The VO₂ films were fabricated in an electron-beam deposition system and annealed in a furnace at atmospheric pressure. The ITO layer enables resistive heating of VO₂ with current pulses, thus allowing modulation of an optical signal transmitted or reflected by the structure. A macroscopic structure with an active area of 50 mm² achieves a modulation frequency of 0.5 kHz. The modulation frequency is limited at the moment by heat dissipation and can be improved in the future. Our results show that VO₂ can be used to build large area optical modulators with high on-off contrast.