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

Christophe Pin,Emmanuel Picard,Frédérique De Fornel,Benoît Cluzel,Emmanuel Hadji,Jean-Baptiste Jager,Manon Tardif,O Fähnle,A Vasdekis

doi:10.1051/epjconf/201921514001

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.

Highlights

Photonic waveguides are commonly used as on-chip optical conveyor belts in on-chip optical trapping and manipulation experiments
Numerical simulation and optical trapping experiments are performed in order to study the periodic modulation of optical forces resulting from the simultaneous excitation of different pairs of guided modes [25]
Because the propagation constant of each mode depends on the wavelength, we can evaluate the variation of the period of the optical force modulation based on numerical simulation results (Figure 1)

Summary

Introduction

Photonic waveguides are commonly used as on-chip optical conveyor belts in on-chip optical trapping and manipulation experiments. Stable optical trapping of particles at a constant position along the waveguide is a more challenging task. In previous works, it required the use of a photonic or plasmonic resonator [11,12,13,14,15,16,17,18,19,20], or the presence of a standing wave along the waveguide, formed by two counter-propagating waves [21,22]. Numerical simulation and optical trapping experiments are performed in order to study the periodic modulation of optical forces resulting from the simultaneous excitation of different pairs of guided modes [25]. We report on the use of such near-field optical lattices in order to handle in various ways the trapped particles [25]

Few-mode silicon waveguides

Near-field optical lattices

Conclusion