Numerical study of exact Purcell factors in finite-size planar photonic crystal waveguides.

The waveguide-length sensitivity on modified spontaneous emission in finite-size planar photonic crystal (PC) waveguides is investigated by numerically computing the exact Purcell (enhanced emission) factor. An unusual dependence on the number of waveguide unit cells and on the waveguide facet truncation is found, allowing one to nanoengineer large Purcell factors in excess of several hundred. Besides having important applications for single-photon sources, these results offer physical insight into the nature of light-matter interactions in miniaturized finite-size PC waveguides, where periodic Bloch-wave analysis breaks down.