With extremely low material absorption and exceptional surface smoothness, silica-based optical resonators can achieve extremely high cavity quality (Q) factors. However, the intrinsic material limitations of silica (e.g., lack of second order nonlinearity) may limit the potential applications of silica-based high Q resonators. Here we report some results in utilizing layer-by-layer self-assembly to functionalize silica microspheres with nonlinear and plasmonic nanomaterials while maintaining Q factors as high as 10(7). We compare experimentally measured Q factors with theoretical estimates, and find good agreement.
In this paper, we present our investigations of the effects of vertical-sidewall roughness (VSR) on guided-mode resonance (GMR) filters made of subwavelength grating for applications to ultrasensitive biosensors operated under IR illumination. We designed the spectral FWHM of the grating filter to be as narrow as possible in order to emphasize the sensitivity and VSR effects. Three types of VSR morphologies on the grating-in terms of the correlation length ? and the rms of the maximum roughness deviation ?-were considered and evaluated. Rigorous coupled-wave analysis was then implemented to quantify the shifts in the reflective resonance peak wavelength value (PWV) of the grating filter. Our simulations show that for specific ? values, the PWVs remain constant even if ? becomes as large as 10?nm; this indicates dramatic bandgaplike stripes, which are similar to the bandgaps observed in the band diagrams of photonic crystals in the ?-? diagram that we have proposed in this study. In other words, the effects of VSR on the GMR biosensor performance are insignificant when ? is located at certain bands; therefore, this type of roughness is highly tolerable even if the linewidth of the filter is decreased to only a few tens of nanometers.
We study the adsorption of gold nanospheres onto cylindrical and spherical glass surfaces from quiescent particle suspensions. The surfaces consist of tapers and microspheres fabricated from optical fibers and were coated with a polycation, enabling irreversible nanosphere adsorption. Our results fit well with theory, which predicts that particle adsorption rates depend strongly on surface geometry and can exceed the planar surface deposition rate by over two orders of magnitude when particle diffusion length is large compared to surface curvature. This is particularly important for plasmonic sensors and other devices fabricated by depositing nanoparticles from suspensions onto surfaces with non-trivial geometries.
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