Shaping the evanescent field of optical nanofibers for cold atom trapping.

We investigate trapping geometries for cold, neutral atoms that can be created in the evanescent field of a tapered optical fibre by combining the fundamental mode with one of the next lowest possible modes, namely the HE(21) mode. Counter propagating red-detuned HE(21) modes are combined with a blue-detuned HE(11) fundamental mode to form a potential in the shape of four intertwined spirals. By changing the polarization from circular to linear in each of the two counter-propagating HE(21) modes simultaneously the 4-helix configuration can be transformed into a lattice configuration. The modification to the 4-helix configuration due to unwanted excitation of the the TE(01) and TM(01) modes is also discussed.