Tunable optofluidic sorting and manipulation on micro-ring resonators from a statistics perspective.

Based on the optical trapping force of an evanescent wave at a micro-ring resonator alongside a waveguide, we propose a tunable optofluidic sorting unit for micro-nanoparticles by localized thermal phase tuning. With the tuning of field build-up factor of resonator, the depth of trapping potential well and the size of trapped particle are adjustable. Furthermore, by considering the Brownian motion of trapped particles from a statistics perspective, we verify the critical trapping threshold of a potential well, which is usually assumed to be 1kBT. The threshold depends not only on the optical power and particle size, but also on the length of the coupling region. Compared with a wavelength tuning mechanism, localized thermal tuning enables large-scale integration of many independent tunable resonators. As a demonstration, we propose a set of operations with three resonators for nanoparticle manipulation, including sorting, storing, and mixing. Our proposed function units are of great importance for on-chip large-scale integration of optofluidic systems.