We investigate the optical and thermal hysteresis of single-domain vanadium dioxide nanocrystals fabricated by ion beam synthesis in a fused silica matrix. The nanocrystals exhibit a giant hysteresis, which permits to optically generate a long-time stable supercooled metallic phase persistent down to practically room temperature. Spatial patterns of supercooled and insulating nanocrystals feature a large dielectric contrast, in particular, for telecom wavelengths. We utilize this contrast to optically imprint reconfigurable photonic elements comprising diffraction gratings as well as on- and off-axis zone plates. The structures allow for highly repetitive (>104) cycling through the phase transition without structural damage.
We propose and implement a new concept for thermochromic plasmonic elements. It is based on vanadium dioxide (VO2) nanocrystals located in the near field of surface plasmon polaritons supported by an otherwise unstructured gold thin film. When the VO2 undergoes the metal-insulator phase transition, the coupling conditions for conversion of light into propagating surface plasmon polaritons change markedly. In particular, we realize thermochromic plasmonic grating couplers with substantial switching contrast as well as tunable plasmonic couplers in a Kretschmann configuration. The use of VO2 nanocrystals permits highly repetitive switching and room temperature operation. Simulations based on the actual dielectric function of our VO2 nanocrystals agree well with the experiment.
We present a comprehensive experimental and theoretical study of the power dependence of coherently controlled currents in bulk GaAs. Currents are optically induced by phase-stable femtosecond ω/2ω pulse pairs. For moderate irradiances, these currents are linked to the third-order optical nonlinearity χ (3) (0; ω,ω,−2ω).Here we focus on elevated irradiances where absorption saturation and ultimately the onset of Rabi oscillations contribute to the optical response. Current diagnostics is achieved electrically by recording the photoresponse of contacted specimens of low temperature grown GaAs as a function of the relative phase of the ω and 2ω pulses. For stronger ω irradiance we find the magnitude of the coherently controlled current to be markedly reduced when compared to the χ (3) expectation dJ /dt ∝ E 2 ω E 2ω . Additional pump-probe type experiments corroborate that this current saturation is indeed predominantly linked to macroscopic band filling. Theoretical simulations for the coherently controlled current based on a 14 band k · p model agree well with the experimental trends.
We demonstrate extension of the distance range of repeaterless Brillouin-OTDR distributed sensing to 250 km by using optical amplification. A single-side interrogation scheme is employed without fiber loops or electrical power on the route.
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