  We investigate numerically and experimentally the properties of a two color
optical fiber taper trap, for which the evanescent field of the modes in the
fiber taper give rise to a three-dimensional trapping potential.
Experimentally, we use the technique to confine colloidal nanoparticles near
the surface of an optical fiber taper, and show that the trapping position of
the particles is adjustable by controlling the relative power of two modes in
the fiber. We also demonstrate a proof of principle application by trapping
quantum dots together with gold nanoparticles in a configuration where the
trapping fields double as the excitation field for the quantum dots. This
scheme will allow the positioning of quantum emitters in order to adjust
coupling to resonators combined with the fiber taper.
