Optical Trapping, Levitation and Tracking of Microparticles Using Waveguides

Abstract

Microparticles are trapped by optical forces created by the evanescent field present on the surface of an optical waveguide. An optical waveguide loop with an intentional gap is used to propel and stably hold the trapped particles. The particles are trapped in the gap of the loop by counter-diverging fields. Simulations indicate that particles trapped in the gap on a strip waveguide will be levitated. In this thesis a waveguide trapping setup is coupled with fluorescence imaging, and an algorithm is used to track the particles in 3 dimensions. The experimental results confirms optical levitation of microparticles trapped in the gap of a strip waveguide. Quantification of the noise associated with the setup and algorithm is performed to determine the precision of the method.

In a separate study, the trapping capabilities of strip and rib waveguides are compared. A rib waveguide loop differs from the strip waveguide loop, in that it has a guiding medium in the gap. This enables stable trapping along the gap, as a downward gradient force is present. Microparticles of different sizes are trapped using the rib waveguide, and a comparison with the strip waveguide is made.