Nonreciprocal switching of VO(2) thin films on microstructured surfaces.

We demonstrate that the combination of near-field focusing and a switchable oxide layer permits construction of a modulator with different optical switching thresholds in two opposing directions. For that purpose VO(2) layers are deposited onto spherical micrometer-sized particles. The phase transition in VO(2) is induced by a nanosecond-pulsed Nd:YAG laser from two different directions. The measured thresholds differ by a factor of 2.4, consistent with calculated differences in the intensities in the two directions.