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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, 00:00 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.