Abstract
The behavior of a negative refraction photonic crystal slab irradiated with out-of-plane incident beam is an unexplored subject. In such an experimental configuration, guided mode resonance appears in the reflection spectrum. We show that, in this case, the light coupled inside the photonic crystal is backpropagating. A relationship with the negative index properties is established using a new approach in which the guided resonance is recovered by modeling the photonic crystal layer with a simple Lorentz resonator using the Fresnel reflection formula. Light incident on a photonic crystal slab can be negatively refracted and thus travel backwards along the slab. This is the finding of Vito Mocella and co-workers from the Institute of Microelectronics and Microsystems in Naples, Italy, and Lawrence Berkeley National Laboratory in the United States. The researchers studied guided resonance in a 1×1 mm2 silicon-on-insulator slab featuring an array of etched air holes arranged in a hexagonal pattern. Illuminating the slab with near-infrared light at a suitable angle from above caused the excitation of guided modes that propagated backwards along the structure and were then captured by an infrared camera. This surprising behaviour, which the researchers also modelled theoretically, is attributed to the negative index of the photonic crystal.
Highlights
In 1902, Wood observed the presence of narrow bright and dark bands in the reflectivity spectrum of an optical grating
The reflection and transmission of an incident wave on a photonic crystal (PhC) slab can produce sharp resonance in the spectrum when the radiation is coupled with the modes of the structure.[5,6,7]
While the in-plane properties of negative refraction in a photonic crystal slab have been studied over the last years,[13,14,15,16,17,18,19,20] this is the first experimental demonstration of negative refraction detected out-of-plane
Summary
In 1902, Wood observed the presence of narrow bright and dark bands in the reflectivity spectrum of an optical grating. These bands were dependent on the polarization of the incident light, and because they could not be explained by grating theory, they were classified as anomalies.[1] This effect was theoretically explained for the first time by Rayleigh[2] and by Hessel and Oliner[3] in 1965, who demonstrated that these anomalies in the reflections from gratings were related to the excitation of surface waves on metallic grating structures. We propose a new theoretical approach to the guided resonance phenomenon, based on the Fresnel formula, which shows very good agreement with the experimental data and which completes the usually adopted phenomenological model[21,22,23] in the context of the Fano resonance approach
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