Analysis of two-dimensional photonic crystal L-type cavities with low-refractive-index material cladding

We have theoretically investigated two-dimensional photonic crystal (2D PC) L1–L21 cavities with low-refractive-index (low- n ) material cladding using the 3D finite-difference time domain method assisted by group theory in the time domain. We investigated various optical properties of 2D PC L-type cavities including resonant frequency, modal symmetry, Q factor, modal volume, real-space distribution, wavevector-space distribution and resonant wavevector condition. The resonant modes in 2D PC L-type cavities are Bloch-like resonant modes. As the size of the cavity increases, the fundamental resonant mode changes from the Fabry–Perot (FP)-like resonant mode to the distributed-feedback (DFB)-like resonant mode with the envelope of the half-cycle sine window. The DFB-like resonant mode can suppress the radiation loss in the vertical direction. The DFB-like resonant mode can achieve a high Q factor ( Q > 10 5 ) in a small cavity ( L < 10 µm). The DFB-like resonant mode is the intrinsic resonant mode in 2D PC L-type cavities, and it is naturally formed without fine tuning. These results show the high potential of 2D PC L-type cavities with low- n material cladding.