ABSTRACT
Metal-based nanohole structures, featuring a continuous matrix and discrete voids, have seen a wide spectrum of practical applications, ranging from plasmonic sensing to extraordinary optical transmission. It would not be uncommon to pursue further enhancement of their optical tunability, and incorporation with other functional materials offers an intriguing lead. In this study, the first step involves colloidal lithography fabrication of gold-based, short-range ordered nanohole structures on a glass substrate with varying geometrical parameters. Plasmonic resonance in optical waveband is readily achieved from the coupling between bonding surface plasmons and nanohole lattices. Resonant features observed in transmission measurements could also be well reproduced both from numerical simulations as well as theoretical calculations based on the grating coupling mechanism. With the introduction of a thin layer of azobenzene compound by spin-coating comes the critical transformation that not only alters optical performances by impacting the surface environment but also bestows the structures with light responsiveness. After 488 nm of laser irradiation, it is observed that the structures underwent cross polarization conversion, which could be attributed to the photoalignment behavior from trans-cis isomerization within the azobenzene layer, yielding further optical tunability with the linearly polarized probe light compared to that in the preirradiated state. The tuning of plasmonic resonances through light stimuli paves a noncontacting path for achieving desired optical responses with potentially high spatial and temporal resolution. This work may serve as a fountainhead for future efforts on optically tailorable photonic devices associated with nanohole plasmonics.
ABSTRACT
In this letter, we report a flexible, all-dielectric metasurface fabricated via nanosphere lithography (NSL) and demonstrate its potentials in sensing applications. Regularly arrayed Si cylinders with hexagonal lattice fabricated on polyethylene terephthalate (PET) flexible substrate are exploited to detect applied strain and surface dielectric environment by measuring transmission spectra. Further numerical simulations coincide with experimental observations. The transmission peak can be attributed to coupled magnetic Mie resonance between close-packed Si cylinders. Such Mie resonance based sensor with high flexibility offers an alternative approach towards detecting surrounding variations besides traditional plasmon resonance based sensors, and provides more choices for designing photonic devices operating in the optical regime.
ABSTRACT
A microwave tunable metamaterial utilizing the semiconductor-to-metal transition of vanadium dioxide (VO2) is proposed, experimentally demonstrated and theoretically scrutinized. Basic concept of the design involves the combination of temperature-dependent hysteresis in VO2 with resonance induced heating, resulting in a nonlinear response to power input. A lithographically prepared gold split-rings resonator (SRR) array deposited with VO2 thin film is fabricated. Transmission spectra analysis shows a clear manifestation of nonlinearity, involving power-dependence of resonant frequency as well as transmitted intensity at both elevated and room temperature. Simulation performed with CST Microwave Studio conforms with the findings. The concept may find applications in transmission modulation and frequency tuning devices working under microwave frequency bands.
