Unexpected unidirectional perfect absorption of light in a freestanding optical thin metallic grating with extremely small filling factor

Abstract

In this paper, we predict an unexpected enhanced optical absorption (OA) phenomenon in an optical thin (60 nm) freestanding metallic grating. After introducing periodical back grooves to the grating, the absorption could be enhanced up to 95% for light incident from the topside, which is inhibited lower than 10% for light incident from the bottom side. Physically it is ascribed to the strong modulation effect of the surface plasmons (SPs)/or charge distribution on the back surface of the grating by the grooves. As a result, the reflection at the SPs resonant position is greatly inhibited. It indicates a new mechanism to achieve high OA in a freestanding subwavelength structure by directly controlling the SPs. More counterintuitively, the highly enhanced absorption will increase as the filling factor of the grating decreases, rather than decrease as the filling factor decreases. So even for a very small filling factor (0.5), unexpected high OA up to 95% could be attained at SPs resonance. The underlying physical mechanism is analyzed with a dipole moment description.

Fano-resonant aluminum and gold nanostructures created with a tunable, up-scalable process

“…This is intuitive as -in contrast to thin film interference, where the resonating wavelength depends on the angle of incidencethe present resonance is confined to the wires. 27,29 Fully exploring this effect would go beyond the scope of this article, but proper tuning of the parameters also led to very high absorbance values (above 95%) in our simulations. The angle of incidence on the other hand determines how strong the incident field can couple to this resonance (weaker coupling at increasing angles of incidence is especially visible for aluminum in the darker blue colors in Fig.…”

“…Research on similar structures however showed that strongly enhanced absorption may result from the introduction of grooves. 27,29 Fully exploring this effect would go beyond the scope of this article, but proper tuning of the parameters also led to very high absorbance values (above 95%) in our simulations.…”

“…26 Several theoretical studies have also investigated the role of Wood-Rayleigh anomalies (WR anomalies), or of various surface plasmon polaritons (SPPs), or groove modes in the optical response of U-shaped wires. [27][28][29][30] Although the oblique deposition process lends itself to low-cost, high-throughput production processes like roll-to-roll manufacturing, 31,32 past findings always relied on the use of noble metals and were limited to small areas since they included either electron beam patterning, 25 particle self-assembly 33 or extreme ultraviolet interference lithography to our knowledge. 34 As a matter of fact, gold and silver, both of which are expensive, are the most used materials in plasmonic nanostructures.…”

Enhancing one dimensional sensitivity with plasmonic coupling

“…First, each cross-grating is demonstrating equivalent sensitivity over a certain range of CDs summing to about one-third of the total range. Second, there is a general trend visible based on the fill factor -the ratio of area filled by the grating to the total area [25] -which is expected due to the nature of localized plasmons.…”

High Broadband Transmission of Light Through a Multi-Layer Sandwich Microstructure Containing a Seamless Metallic Film

“…For these optoelectronic devices, a high transmission of light through MF is necessary. A simple way to enhance the transmission is to carve channels (holes or slits) in the MF, for which the extraordinary optical transmission phenomena of lights were observed [1]- [5], which are widely explained as the excitation of surface plasmons resonance [1]- [4] or spoof surface plasmons for highly conducting metals [6] and/or the Fabry-Pérot (FP)-like cavity mode resonances in these optical channels [5], [7]. However, these transmissions are usually narrowband due to their resonant nature.…”