Investigation on photonic crystal nanobeam cavity based on mixed diamond–circular holes

A photonic crystal nanobeam cavity (M-PCNC) with a structure incorporating a mixture of diamond-shaped and circular air holes is proposed. The performance of the cavity is simulated and studied theoretically. Using the finite-difference time-domain method, the parameters of the M-PCNC, including cavity thickness and width, lattice constant, and radii and numbers of holes, are optimized, with the quality factor Q and mode volume Vm as performance indicators. Mutual modulation of the lattice constant and hole radius enable the proposed M-PCNC to realize outstanding performance. The optimized cavity possesses a high quality factor Q = 1.45 × 105 and an ultra-small mode volume Vm = 0.01(λ/n) [Zeng et al., Opt Lett 2023:48;3981–3984] in the telecommunications wavelength range. Light can be progressively squeezed in both the propagation direction and the perpendicular in-plane direction by a series of interlocked anti-slots and slots in the diamond-shaped hole structure. Thereby, the energy can be confined within a small mode volume to achieve an ultra-high Q/Vm ratio.