Tunable optical lattices in the near-field of a few-mode nanophotonic waveguide

¹ Groupe Optique de Champ Proche – L.R.C. SiNOPTIQ du C.E.A. n°DSM-08-36, Laboratoire Interdisciplinaire Carnot de Bourgogne U.M.R. C.N.R.S. 6303, Université de Bourgogne-Franche Comté, 9. Av. A. Savary, 21078 Dijon, France
² Université Grenoble Alpes, C.E.A., I.N.A.C., PHELIQS, SINAPS, F-38000 Grenoble, France
^# Current address: RIES, Hokkaido University, Kita 20-jo Nishi 10-chome, Kita-ku, Sapporo, Hokkaido, 001-0020, Japan

^* Corresponding author: benoit.cluzel@u-bourgogne.fr

Published online: 10 September 2019

Abstract

Due to the action of the scattering force, particles that are optically trapped at the surface of a waveguide are propelled in the direction of the light propagation. In this work, we demonstrate an original approach for creating tunable periodic arrays of optical traps along a few-mode silicon nanophotonic waveguide. We show how the near-field optical forces at the surface of the waveguide are periodically modulated when two guided modes with different propagation constants are simultaneously excited. The phenomenon is used to achieve stable trapping of a large number of dielectric particles or bacteria along a single waveguide. By controlling the light coupling conditions and the laser wavelength, we investigate several techniques for manipulating the trapped particles. Especially, we demonstrate that the period of the optical lattice can be finely tuned by adjusting the laser wavelength. This effect can be used to control the trap positions, and thus transport the trapped particles in both directions along the waveguide.