Optical forces and trapping potentials of a dual-waveguide trap based on multimode solid-core waveguides

We propose a novel design of the dual-waveguide trap for trapping and Raman identification of microscopic particles and biological objects in a fluid. The device is based on two embedded Si3N4 waveguides launching counterpropagating beams into the fluidic channel of a lab-on-a-chip. For waveguides with a square cross-section of 1 mu m(2), a 5 m m gap in between and for a 785 nm operation wavelength, we perform finite-difference time-domain simulations of the beam profiles and the trapping forces acting on polystyrene beads (diameter 0.2-1.4 mu m). The forces reach values up to 16 pN/W for a bead diameter of 1.4 mu m, indicating that the trap is very suitable to trap particles in a fluid. This is confirmed by the trapping potentials deduced from the force curves. The design of waveguides and chip is completely compatible with glass-based microfluidic technology, thus enabling mass production and widespead application, contrary to previous approaches. [DOI: 10.2971/jeos.2011.11022]