Abstract

Because of the diffraction limit, optical trapping of single sub-micron sized dielectric particles with classical optical tweezers requires the use of large power to have a field gradient sufficiently strong. The laser focus spot has a minimum size that is related to the diffraction limit and impose the use of such large powers. Photonic crystal cavities are an efficient way to circumvent this limit by confining the light within a mode volume that is below the diffraction limit imposed by the wavelength of the laser light source [1]. In this work, we use hollow photonic crystal cavities etched in a silicon membrane to increase the field overlap with the singly trapped sub-micron sized particle. The device is fabricated from a silicon on isolator wafer (SOI) of 250 µm of total thickness and is operating at a wavelength of 1550 nm [2]. Submicron sized polystyrene spheres are carried to the trapping sites using a hybrid glass/PDMS (polydimethylsiloxane) microfluidic circuit. The microfluidic layer thickness is 470 µm, composed of a glass membrane of 450 µm and a PDMS layer of 20 µm. The thickness of the whole device is reduced to improve the optical qualities for imaging and detection of the nanoparticles. Because of the strong confinement of light in the cavity, laser power as low as 100 µW in the waveguide can be used in order to trap a 500 nm polystyrene particle for any amount of time.

© 2015 IEEE