Tunable structures comprising two photonic crystal slabs – optical study in view of multi-analyte enhanced detection

Lina Shi,Yves-Alain Peter,Maksim Skorobogatiy,Pierre Pottier

doi:10.1364/oe.17.010623

Abstract

Using finite-difference time-domain method, we characterize the normal-incidence transmission properties of a two slab photonic crystal device in a view of its applications in fluorescence enhancement and multi-analyte detection. Individual slabs consist of a square or a triangular lattice of air holes embedded into a silicon nitride slab. The geometrical parameters are chosen so that the individual slabs operate in a guided resonance regime where strong reflectivity under the normal incidence angle is observed in a broad spectral range. When placed in the close proximity of each other, the two photonic crystal slab system exhibits a narrow Fabry-Perot type transmission peak corresponding to the excitation of a resonant mode in the cavity formed by the two slabs. We then study the effects of the size of the air gap between the two photonic crystal slabs on the spectral position and bandwidth of a resonance transmission peak. Finally, we investigate the electromagnetic energy distributions at the wavelength of a transmission resonance in the double slab photonic crystals. As a final result we demonstrate that this structure can provide electric field enhancement at the slab surface, which can be used for fluorescence enhancement.

Highlights

Fluorescence is important to both in-vivo cellular imaging and in-vitro assay detection.[1,2] The importance of fluorescence-based detection methods has motivated engineering of optically active structures capable of enhancing the fluorescent signal
With a goal of miniaturization of the multi-analyte detection systems, in this paper we report a structure based on a two Photonic crystal (PhC) slab geometry that can enhance the fluorescence signal from quantum dots (QDs) emitting at several distinct wavelengths
For a given hole radius r = 0.1a, 0.2a, 0.3a, 0.35a, 0.4a, 0.45a, the reflection spectra of the PhC slabs are calculated for ten values of the slab thicknesses t = 0.1a, 0.2a, ..., 1.0a for both the square and triangular lattices

Summary

Introduction

Fluorescence is important to both in-vivo cellular imaging and in-vitro assay detection.[1,2] The importance of fluorescence-based detection methods has motivated engineering of optically active structures capable of enhancing the fluorescent signal. Multi-analyte detection of different pathogens needs different fluorescent labels having different emission wavelengths. In order to realize multi-analyte detection, one should, enhance fluorescence at several distinct wavelengths corresponding to the emission wavelengths of the fluorescent labels under consideration. Sensing systems for the detection of common diseases are in great need of miniaturization and low cost fabrication processes to be suited for point of care diagnostics. To this end, Mathias et al.[5] have fabricated a PhC with a graded thickness TiO2 layer which contains reflective resonant peaks for a range of positiondependent wavelengths spanning 100 nm. Ganesh et al.[6] have shown that the device can be used to excite a broad range of resonant wavelengths by controlling the launching angle

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Conclusion