All-Optical Particle Manipulation by Evanescently Coupled Photonic Resonators
The video below demonstrates the trapping and transport of 500nm polystyrene particles on a single-mode silicon waveguide. In addition, an evanescently coupled 1-dimensional (1D) photonic crystal resonator acts as a static point trap. The enhancement (amplification) of the optical field within the resonator coupled with the extremely large field gradients produces a very strong, stationary trap that is capable of trapping particles well below the conventional limitations imposed by traditional optical tweezing.
This video shows 500nm particles being trapped and propagated along a waveguide. The particle are propelled along the waveguide due to the scattering forces generated from the propagating component of the optical field within the waveguide. The laser is tuned to the resonant wavelength of the resonator. As a result the particles propagate along the waveguide and then jump onto the static resonant trap (since the resonator is a much stronger trap as compared to the waveguide). Once the particle is statically trapped on the resonator it can either be returned back to the waveguide to propagate further along the waveguide, or it can be expelled, depending on the direction of fluid flow in the microfluidic channel. Particle release from the resonant trap is achieved by detuning the laser wavelength away from the resonance. In this video you will observe a trapped particle returned to the waveguide. Subsequently another particle is trapped onto the resonator. By reversing the flow in the channel, this particle is now convected away with the flow instead of being returned onto the waveguide. This process is repeated. Finally all the trapped particles are released by turning the laser off.
Trapping of Nanoparticles - Going Beyond the Diffraction Limit
The video below demonstrates the trapping of a 100nm polystyrene microsphere on a 1D resonator. The resonator acts as an extremely small, strong, static point trap. It is possible to trap particles as small as 25nm with these devices. The particle is released by detuning the laser away from the resonant wavelength.