Photonic band gap materials: semiconductors of light

Photonic Band Gap (PBG) materials are artificial, periodic, dielectrics that enable engineering of the most fundamental properties of electromagnetic waves. These include the laws of refraction, diffraction, and spontaneous emission of light. Unlike traditional semiconductors that rely on the propagation of electrons through an atomic lattice, PBG materials execute their novel functions through selective trapping or “localization of light”. Three dimensional (3D) PBG materials offer a unique opportunity to simultaneously (i) synthesize micron-scale 3D optical circuits that do not suffer from diffractive losses and (ii) engineer the electromagnetic vacuum density of states in this 3D optical micro-chip. This combined capability opens a new frontier in integrated optics as well as the basic science of radiation-matter interactions.

I review recent approaches to micro-fabrication of photonic crystals with a large 3D PBG centered near 1.5 microns. These include direct laser-writing techniques, holographic lithography, silicon double inversion, and a newly invented optical phase mask lithography technique.

I discuss resonant nonlinearities associated with the embedding of quantum dots in PBG wave-guides. By suitable engineering the electromagnetic vacuum, it is possible to induce population inversion through coherent resonant optical pumping of the quantum dots. This enables sub-picosecond switching of optical pulses using optical holding and gate fields of less than one milli-Watt power.

Finally, I describe a novel and fundamental quantum mechanical effect predicted to occur in carefully fabricated PBG-Quantum Well Hetero-structures. We suggest that the dynamics of bound electron-hole pairs (excitons) in the quantum well can be significantly modified by the PBG environment. In particular, the exciton acquires a very large electromagnetically-induced mobility as well as long lifetime, when its radiative recombination energy coincides with a photonic band edge. This may enable Bose condensation of excitons at elevated temperatures.

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