Design of two-dimensional photonic crystal nanocavities with low-refractive-index material cladding

We have theoretically investigated two-dimensional photonic crystal (2D PC) nanocavities with low-refractive-index (low-n) material cladding using a 3D finite-difference time-domain method. When the refractive index of the cladding is increased from 1 to 1.535, corresponding to that of organic polymers, the Q factor markedly decreases (Q < 10(3)). We finely adjusted the positions of the holes at both edges of the 2D PC nanocavities. The Q factor can be increased by a factor of up to 21 (Q > 10(4)) by shifting the neighboring four pairs of holes inward by suitable amounts. In addition, we examined the real and wavevector space distributions of the resonant modes. We revealed significant design rules based on single and double Gaussian envelope functions, which can be used to effectively and flexibly develop and finely adjust the optical properties of 2D PC nanocavities with low-n material cladding.