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Layout of the one-dimensional photonic crystal slab displaying guided-mode resonances. The structure is comprised of a low refractive index polymer containing a one-dimensional periodic structure attached to a glass substrate and coated with a high index layer of . The physical parameters of the device, refractive indices of the materials and the launch angle of the incident beam set the resonance wavelength
Calculated resonant mode band structure for the one-dimensional photonic crystal structure, shown for (a) TE polarized incidence and (b) TM polarized incidence. The axis shows the spectral location of the resonance for a given incident angle in degrees (wave vector, axis). The color scale shows the far-field reflectivity of the resonance, and the width of the bands are inversely related to the resonance factor.
Calculated near-electric field intensity profiles for the resonant modes at for (a) TE polarized incidence, showing enhancement of only the field component and TM polarized incidence showing enhancement of both (b) and (c) field components. The color scale associated with each figure represents the intensity of the electric field and is normalized to the unit intensity incident wave.
(a) Exponential decay of the electric field intensity on the surface of the device as a function of the thickness of the spacer, as calculated by RCWA. The decay length of the field intensity was . (b) Experimentally determined falloff of the fluorescence enhancement factor for Cy-5 as a function of the thickness of layer deposited. The decay length determined by experiment was . Both calculations and experiments were performed for an incident wavelength of .
Fluorescence scans off (left) and on (right) resonance measured for a spacer layer thickness , showing the enhanced fluorescence effect. The plot below the figure shows the intensity profile on the sensor surface as a function of position, as marked by the line on the fluorescence scans.
Variation of the decay length with the resonance wavelength: Calculated decay lengths (normalized to the decay length at ) as a function of the resonant wavelength. The relationship is approximately linear in the wavelength range where the dispersion of the materials is small. Toward lower wavelengths, the increasing index of the materials causes greater confinement of the resonant mode resulting in the observed nonlinearity.
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