4.1. Introduction

Since 1990, Cavity Quantum ElectroDynamics (CQED) has become a major source of inspiration for basic research in optoelectronics [BUR 95; WEI 96; DUC 96; BEN 98]. In the 1980s, a beautiful series of experiments on atoms in microwave and optical cavities had demonstrated that optical processes including spontaneous emission (SE) can be deeply modified using a cavity to tailor the emitter-field coupling [HAR 89].

Among other effects observable in the so called weak coupling regime , the modification of the emission diagram, the enhancement or inhibition of the SE rate, the funneling of SE photons into a single mode and the control of the SE process on the single photon level are particularly attractive for applications in optoelectronics. For very high-Q (i.e. weakly damped) cavities, SE can even become a reversible process, in the so called strong-coupling regime .

Improving control over spontaneous emission processes in optoelectronic devices was recognized in the mid-1980s as a promising avenue for improving the performance of light emitting diodes and lazer diodes. In lazers, for instance, photons that are spontaneously emitted into the lasing mode(s) act as seeds for amplification by stimulated emission. Conversely, SE into other modes is useless and even detrimental, as it consumes a significant amount of the injected electron-hole pairs.

By increasing the fraction ? of the SE that is coupled to the lasing mode, one can reduce (roughly in inverse proportion) the threshold current of the lazer. Novel devices based on...