Opal-based composites as photonic crystals

The photonic energy band structure of a 3D, face-centred cubic package of silica balls (synthetic opal) was studied for both the positive refractive index (RI) contrast (RT_ball>RI_void) and inverted contrast (RT_ball<RI_void) situations. The inverted situation was obtained by impregnation of interstitial voids with a high-RI semiconductor. Following the inversion of the scattering ensemble, a dramatic change in the stop-bandwidth and angular dispersion of the stop-band were observed. The spontaneous emission from an incomplete photonic crystal is anisotropic to an extent which depends on the angular dispersion of the stop-band: it is suppressed in the middle of the stop-band and amplified at the stop-band edges. The amplified spontaneous emission (ASE) regime is the result of interplay between the photonic and electronic energy bandstructures of the photonic crystal. This effect is considered to be a precursor for stimulated emission