Efficient particle collection using concentric optical ring array

Trapping is the first as well as the most important step in various optical manipulations. However, when the concentration of sample is extremely low, optical trapping cannot be performed efficiently because the samples are usually out of the action radius of the trapping well. In this paper, numerical simulation results are presented to illustrate an active and efficient optical collection mechanism. We propose the optical collection mechanism by using an array of concentric dielectric rings, in which a series of nanoholes are introduced with optimized separations and radius to form trapping centers. When the incident wavelength is tuned in order, the trapped particles will be transferred from an outer ring to its inner neighboring ring, and finally be collected to the center of the rings. The mechanism reported here paves the way for efficient particle collection, and may find potential applications in various optical manipulations.