Photonic crystal nanobeam/micro-ring hybrid-cavities for optical trapping

We propose a new type of hybrid-cavity structure for trapping nanoscale particles. The hybrid cavity is based on a ring waveguide with the incorporation of a photonic crystal nanobeam cavity (PCNC). We design the cavity and investigate the influence of geometric parameters on its performance and optical trapping ability. The numerical results show that high quality factor, low mode volume and strong optical trapping ability can be achieved. The radii of holes are quadratically tapered from the center to two sides with a smaller period in the mirrors of the PCNC and the optical trapping force is proportional to (1−T)Q/V of the cavity. Furthermore, a hybrid cavity with optimal trapping ability is realized with quality factor up to 1.98×106, mode volume as low as 1.90(λ∕nSi)3 and its optical trapping force can be as high as −855 pN/mW, which is 15 times enhanced compared to that of a microring resonator with the same radius.