Liquid-based optical waveguide and its application for particle manipulation

Abstract

In this thesis, development of liquid-based optical waveguide system, so-called optofluidic waveguide, in a microfluidic platform and its application to the optical particle manipulation were studied. In order to overcome the limitations of the two-dimensional liquid-core/liquid-cladding (L2) optical waveguide, which was previously reported, a three-dimensional microfluidic L2 optical waveguide system was demonstrated in a simple single-layer. The core fluid was focused in the vertical direction by a transverse secondary flow (produced by a Dean vortex) and focused in the horizontal direction by two parallel sheath flows. The waveguide intro-duced less optical loss between the core fluid and the channel wall. Diffusion between the core fluid and the cladding fluid was reduced by high fluid velocities. The present system can be considered as a graded-index (GRIN) waveguide due to the diffusion effect between core and cladding liquids. The width of the core fluid was manipulated by adjusting the sheath flow rates. Numerical simulations were conducted to support and interpret the experimental results. Next, for the application of the L2 optical waveguide, optofluidic particle manipulation in a L2 optical waveguide was considered. For the fundamental study, the force equations de-scribing the radiation forces on a microsphere in an arbitrary refractive index profile were de-rived here using the photon-stream method in a ray-optics regime. A loosely focused Gaussian beam was employed as the radiating illumination beam. The radiation forces on a spherical microsphere were calculated in a time-varying refractive index profile. The refractive index profile of the surrounding medium was evaluated according to the concentration distribution obtained from the diffusion equation. The scattering and gradient forces on a microsphere were calculated for different refractive indices (1.22, 1.33, 1.43, and 1.59), and the radiation forces on a perfectly reflecting microsphere w...