Field-Matter Interactions in Photonic Bandgaps

Abstract

Inhibition of spontaneous emission (ISE) has been demonstrated in the past for molecules near a reflecting surface1 and for Rydberg atoms in microwave cavities.2 In these systems the destructive interference imposed by the boundary conditions on spontaneous emission is sensitive to microscopic changes in the location of the emitter or in the cavity size, as well as to emitters’ polarization.3 Recently, the possibility of obtaining ISE in spectral bands of forbidden light propagation (photonic bandgaps) has been suggested by Yablonovitch.4 These bandgaps are spectral regions admitting only complex wavevectors k (evanescent waves) in any direction, and bounded by frequencies ωmax(min) which the dispersion curve ω(k) becomes discontinuous. Because they are associated with definite k (band edges), such bandgaps are delocalized in space, i.e., they inhibit spontaneous emission independently of the spatial distribution of emitters in the system. The systems that have been proposed4 for the demonstration of bandgaps are dielectric superlattices that exhibit strong three-dimensional (3D) periodic modulations of the dielectric index with a period comparable to half the emission wavelength. The consideration of bandgaps is motivated also by the quest for strong localization of light, i.e., local modes extending over distances of the order of a wavelength. Such modes are predicted by John to occur near the edge of photonic bandgaps in partially disordered structures.5 They can be produced by point or line “defects” altering the strength or periodicity of the dielectric index, or by a “phase slip” in the dielectric superlattice, which is the 3D analog of phase delays introduced into one-dimensional periodic gratings in distributed-feedback lasers.4