  We present a heuristic mathematical model of the relation between the
geometry of a photonic crystal waveguide and the Purcell enhancement factor at
a particular wavelength of interest. We use this model to propose approaches to
the design of a photonic crystal waveguide maximizing the Purcell enhancement
at a target wavelength. Numerical simulations indicate that the proposed
structures exhibit robustness to fabrication defects introduced into photonic
crystal geometry.
