Vortex beams that carry orbital angular momentum (OAM) have garnered significant attention, as they bring the degree of freedom of OAM to modern optical communication, beyond the traditional degrees of freedom such as amplitude, phase and polarization. Meanwhile, metasurfaces composed of ultra-thin layers of subwavelength structures have also been utilized for light manipulation. Nevertheless, the combination of these two concepts has not been explored in the form of microring resonator-based light emitter. In this work, we demonstrate a Si-based, passive, conjugate symmetrybreaking emitter in numerical simulation. This broken conjugate symmetry enables the emitter to generate OAMs with different topological charges, when it is driven at two opposite input directions.
Uncooled microbolometric photodetection is a key technology for low cost, reliable and lightweight infrared sensing but suffers in performance compared to cooled photodetectors. Introducing new microbolometer functionality such as wavelength and polarisation sensitivity will improve current device performance and encourage new market opportunities. One method is to introduce metallic nanostructures, which are widely known to exhibit strong localised surface plasmon resonances (LSPR) that are sensitive to incident wavelength and polarisation. This work presents the integration of plasmonic silver nanorods into the material vanadium dioxide VO2. An experimental correlation between suppression of VO2 resistivity and dips in transmission spectra was observed. Subsequent optical and thermal simulations of VO2 films, both on sapphire Al2O3 and suspended in air, demonstrate how LSPR-driven electric field enhancement leads to localised heating around the nanorods and subsequent temperature distribution on the nanoscale. This work opens the path to a broad family of photodetection functionalities for vanadium dioxide-based microbolometers.
Selective excitation of specific multipolar resonances in matter can be of great utility in understanding the internal make-up of the underlying material and, as a result, in developing novel nanophotonic devices. Many efforts have been addressed on this topic. For example, the emission spectra related to the different multipolar transitions of trivalent europium can be modulated by changing the thickness of the dielectric spacer between the gold mirror and the fluorescent layer. In this talk, we reported the results about active control of the multipolar resonance in metadevices using the coherent control technique. In the coherent control spectroscopy system, the optical standing wave constructed from two counterpart propagation coherent beams is utilized as the excitation. By controlling the time delay between two ultrafast pulses to decide the location of metadivce as the electromagnetic field node or antinode node of standing wave, the absorption related to the specific multipolar resonance can be controlled. Using this technique, with the 30-nm-thick metadevice, the broadband controlling light with light without nonlinearity can be realized. The switching contrast ratios can be as high as 3:1 with a modulation bandwidth in excess of 2 THz. The active control of the high order and complex optical resonance related to the magnetic dipole, electric quadrupole, and toroidal dipole in the metamaterial is reported as well. This research can be applied in the all ultrafast all-optical data processing and the active control of the resonances of metadevice with high order multipolar resonance.
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