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Limiting Optical Diodes Enabled by the Phase Transition of Vanadium Dioxide

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journal contribution
posted on 20.06.2018 by Chenghao Wan, Erik H. Horak, Jonathan King, Jad Salman, Zhen Zhang, You Zhou, Patrick Roney, Bradley Gundlach, Shriram Ramanathan, Randall H. Goldsmith, Mikhail A. Kats
A limiting optical diode is an asymmetric nonlinear device that is bidirectionally transparent at low power but becomes opaque when illuminated by sufficiently intense light incident from a particular direction. We explore the use of a phase-transition material, vanadium dioxide (VO2), as an active element of limiting optical diodes. The VO2 phase transition can be triggered by optical absorption, resulting in a change in refractive index orders of magnitude larger than what can be achieved with conventional nonlinearities. As a result, a limiting optical diode based on incident-direction-dependent absorption in a VO2 layer can be very thin, and can function at low powers without field enhancement, resulting in broadband operation. We demonstrate a simple thin-film limiting optical diode comprising a transparent substrate, a VO2 film, and a semitransparent metallic layer. For sufficiently high incident intensity, our proof-of-concept device realizes broadband asymmetric transmission across the near-infrared, and is approximately ten times thinner than the free-space wavelength.