Investigation of defect cavities formed in three-dimensional woodpile photonic crystals

We report the optimization of optical properties of single defects in three-dimensional (3D) face-centered-cubic (FCC) woodpile photonic crystal (PC) cavities by using plane-wave expansion (PWE) and finite-difference time-domain (FDTD) methods. By optimizing the dimensions of a 3D woodpile PC, wide photonic band gaps (PBG) are created. Optical cavities with resonances in the bandgap arise when point defects are introduced in the crystal. Three types of single defects are investigated in high refractive index contrast (gallium phosphide–air) woodpile structures, and Q-factors and mode volumes (Veff) of the resonant cavity modes are calculated. We show that, by introducing an air buffer around a single defect, smaller mode volumes can be obtained. We demonstrate high Q-factors up to 700,000 and cavity volumes down to Veff<0.2(λ/n)3. The estimates of Q and Veff are then used to quantify the enhancement of spontaneous emission and the possibility of achieving strong coupling with nitrogen-vacancy (NV) color centers in diamond.