Abstract
The article focuses on depth-dependent visible band transmission effects in a symmetrical “insulator-metal-insulator” diffraction system based on a variable depth grating. These effects were studied both experimentally and theoretically in TM and TE polarizations. In particular, the existence of an optimized grating depth for plasmon-mediated resonant transmission was confirmed experimentally, and differences in TE and TM transmission behavior are discussed. We utilize a simple and flexible fabrication approach for rapid synthesis of apodized structures with adiabatically varying depth based on a beat pattern of two interferential lithography exposures. The present study can be useful in the fields of transmission-based optical security elements and biosensors.
Highlights
The article focuses on depth-dependent visible band transmission effects in a symmetrical “insulatormetal-insulator” diffraction system based on a variable depth grating
In this work we focus on the study of multidimensional metallic gratings which support the resonant transmission effect
Resonances in grating-based optical elements substantially depend on the depth[28], and in this work we have developed a simple and flexible fabrication technology which allows one to rapidly create apodized structures with adiabatically varying depth
Summary
An advantage of the described variable-depth grating fabrication approach is that instead of synthesizing series of samples of different depth, all possible depths in a specified range are present at once. The numerically calculated transmission (Fig. 5c), using the Generalized Source Method (GSM)[35], reproduces all features of the experimental data including the positions of the vertical waveguide lines, a broad plasmon-mediated transmission area in the region of 500–600 nm wavelength, and the highest TM-transmission point A. This figure indicates firstly the wavelength splitting of waveguide and plasmonic modes and confirms that the plasmon-mediated resonant transmission area can be broad (50 nm for a depth of 70 nm in the wavelength range of 500–550 nm at normal incidence). This figure clarifies that enhanced TE transmission observed experimentally appears due to the Fabry-Pérot resonances and does not depend on waveguide modes and the grating period. The estimated inaccuracy of the metal deposition thickness of ≈10% gives a noticeable variation of transmission as the average metal thickness of 17 nm is very small
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