Diffusion-controlled optical elements for optofluidics

Diffusion at the interface between two streams of liquids with different refractive indices, flowing laminarly, creates a controllable concentration gradient and a corresponding refractive index gradient. Using flow rate to change the time over which diffusion occurs in a liquid-liquid (L-2) optical waveguide, we demonstrate an optical splitter and a wavelength filter. The optical splitter comprises two parallel L-2 waveguides which smoothly merge into a single L-2 waveguide by diffusion. The wavelength filter comprises an optical splitter in which the two L-2 waveguides contain an absorbing dye. (C) 2005 American Institute of Physics.