title: Spatial Resolution and Refractive Index Contrast of Resonant Photonic Crystal Surfaces for Biosensing.
abstract: By depositing a resolution test pattern on top of a Si3N4photonic crystal resonant surface, we have measured the dependence of spatial resolution on refractive index contrast Δn. Our experimental results and finite-difference time-domain (FDTD) simulations at different refractive index contrasts show that the spatial resolution of our device reduces with reduced contrast, which is an important consideration in biosensing, where the contrast may be of order 10-2. We also compare 1-D and 2-D gratings, taking into account different incidence polarizations, leading to a better understanding of the excitation and propagation of the resonant modes in these structures, as well as how this contributes to the spatial resolution. At Δn= 0.077, we observe resolutions of 2 and 6μm parallel to and perpendicular to the grooves of a 1-D grating, respectively, and show that for polarized illumination of a 2-D grating, resolution remains asymmetrical. Illumination of a 2-D grating at 45° results in symmetric resolution. At very low index contrast, the resolution worsens dramatically, particularly for Δn< 0.01, where we observe a resolution exceeding 10μm for our device. In addition, we measure a reduction in the resonance linewidth as the index contrast becomes lower, corresponding to a longer resonant mode propagation length in the structure and contributing to the change in spatial resolution.
authors.affiliation: Department of Physics, University of York, York YO24 1UB, U.K.
authors.forename: G J
authors.initials: GJ
authors.lastname: Triggs
authors.affiliation: Department of Physics, University of York, York YO24 1UB, U.K.
authors.forename: M
authors.initials: M
authors.lastname: Fischer
authors.affiliation: Department of Physics, University of York, York YO24 1UB, U.K.
authors.forename: D
authors.initials: D
authors.lastname: Stellinga
authors.affiliation: Department of Physics, University of York, York YO24 1UB, U.K.
authors.forename: M G
authors.initials: MG
authors.lastname: Scullion
authors.affiliation: Department of Biology and Hull York Medical School, University of York, York, YO24 1UB, U.K.
authors.forename: G J O
authors.initials: GJ
authors.lastname: Evans
authors.affiliation: Department of Physics, University of York, York YO24 1UB, U.K.
authors.forename: T F
authors.initials: TF
authors.lastname: Krauss
keywords: Resonant surface; biosensor; grating; photonic crystal; polarization; refractive index contrast; spatial resolution