Q-factor optimization for TM-like modes in pillar-based photonic crystal cavities with planar slot waveguides

We propose a design for high Q-factor, pillar-based photonic crystal cavities, with the goal of enhancing radiation–matter interaction in planar slot waveguides. The Q-factor is optimized for transverse-magnetic-like (TM-like) cavity modes, and it is found that a maximum Q ~ 45000 can be reached by proper design of the pillars defining the cavity region. As an application, we study the Purcell enhancement of spontaneous emission rate for a dipole emitter within a thin layer of low index material (slot) grown at the pillars center. The field intensity is enhanced within the slot for TM-like modes, which yields a Purcell factor of the order of 10000, larger than the corresponding structure without slot. These results directly apply to nanostructures made of a thin active layer of erbium-doped silicon dioxide embedded in silicon pillars, which can be readily fabricated with state-of-the art technology.