Unidirectional vertical emission from photonic crystal nanolasers

Here, we emphasize the importance of using a bottom reflector to achieve unidirectional vertical emission from an ultra-small light emitter. Specifically, we have considered a photonic crystal slab nanocavity laser placed in the vicinity of a perfect mirror. By choosing near one-wavelength distance between the bottom reflector and the cavity, over 80% of photons generated inside the laser cavity can funnel into a small divergence angle of plusmn30deg. It is also interesting to observe that the natural radiation rate (~1/Q factor) of the nanocavity mode can be modified by varying the gap size, which is analogous to the famous cavity quantum electrodynamics effect for a point dipole source placed near a perfect mirror. A simple, comprehensive plane wave interference model is presented to explain the observed over six-fold vertical emission enhancement. Furthermore, we propose some of the very practical nanolaser designs based on a metal bonding technology, which may enable continuous current injection operation at room-temperature.