Abstract

We report what is to our knowledge the first observation of the effect of parallel-to-interface-refraction (PIR) in a three-dimensional, simple-cubic photonic-crystal. PIR is an acutely negative refraction of light inside a photonic-crystal, leading to light-bending by nearly 90 deg over broad wavelengths ($\lambda$). The consequence is a longer path length of light in the medium and an improved light absorption beyond the Lambertian limit. As an illustration of the effect, we show near-unity total absorption ($\ge 98\%$) in $\lambda =520–620\mathrm{nm}$ and an average absorption of $\sim 94\%$ over $\lambda =400–700\mathrm{nm}$ for our $\alpha$-Si:H photonic-crystal sample of an equivalent bulk thickness of $\tilde{t}=450\mathrm{nm}$. Furthermore, we have achieved an ultra-wide angular acceptance of light over $\theta =0°–80°$. This demonstration opens up a new door for light trapping and near-unity solar absorption over broad $\lambda$s and wide angles.

© 2013 Optical Society of America

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