Opal-based composites as photonic crystals

The photonic energy band structure of a 3D, face-centred cubic package of s ilica balls (synthetic opal) was studied for both the positive refractive i ndex (Ri) contrast (RIball > RIvoid) and inverted contrast (RIball <RIvoid) situations. The inverted situation was obtained by impregnation of interst itial voids with a high-RI semiconductor. Following the inversion of the sc attering ensemble. a dramatic change in the stop-bandwidth and angular disp ersion of the stop-band were observed. The spontaneous emission from an inc omplete photonic crystal is anisotropic to an extent which depends on the a ngular dispersion of the stop-band: it is suppressed in the middle of the s top-band and amplified at the stop-band edges, The amplified spontaneous em ission (ASE) regime is the result of interplay between the photonic and ele ctronic energy bandstructures of the photonic crystal. This effect is consi dered to be a precursor for stimulated emission.