Long-range optical trapping and binding of microparticles in hollow-core photonic crystal fibre

Dmitry S Bykov,Philip St.J Russell,Shangran Xie,Tijmen G Euser,Andrey Machnev,Gordon K L Wong,Richard Zeltner

doi:10.1038/s41377-018-0015-z

Abstract

Optically levitated micro- and nanoparticles offer an ideal playground for investigating photon–phonon interactions over macroscopic distances. Here we report the observation of long-range optical binding of multiple levitated microparticles, mediated by intermodal scattering and interference inside the evacuated core of a hollow-core photonic crystal fibre (HC-PCF). Three polystyrene particles with a diameter of 1 µm are stably bound together with an inter-particle distance of ~40 μm, or 50 times longer than the wavelength of the trapping laser. The levitated bound-particle array can be translated to-and-fro over centimetre distances along the fibre. When evacuated to a gas pressure of 6 mbar, the collective mechanical modes of the bound-particle array are able to be observed. The measured inter-particle distance at equilibrium and mechanical eigenfrequencies are supported by a novel analytical formalism modelling the dynamics of the binding process. The HC-PCF system offers a unique platform for investigating the rich optomechanical dynamics of arrays of levitated particles in a well-isolated and protected environment.

Highlights

Introduction SinceAshkin’s first report of the acceleration and trapping of microparticles by optical forces[1], the use of optical tweezers has developed into a standard technique for biological manipulation and pico-Newton force sensing[2,3], to mention just two examples from a wide range of applications
The pulses were split at a polarising beam splitter (PBS) and coupled into the opposite ends of an 8 cm length of hollow-core photonic crystal fibre (HC-PCF) with a core diameter of 7.8 μm, which was mounted inside a vacuum chamber
When light is launched into the HC-PCF, it is difficult to avoid weak excitation of higher-order modes (HOMs)

Summary

Introduction

Introduction SinceAshkin’s first report of the acceleration and trapping of microparticles by optical forces[1], the use of optical tweezers has developed into a standard technique for biological manipulation and pico-Newton force sensing[2,3], to mention just two examples from a wide range of applications. Especially at low gas pressure, is isolated from the external environment, resulting in very low mechanical damping. This leads to very-high mechanical Q-factors and permits particle rotational speeds in the MHz range[4,5]. Multiple trapping sites have previously been created using interference[17] and holographic tweezers[18], allowing the formation of a lattice of trapped microparticles In these experiments, there is typically very-little multiple scattering between particles—a necessary prerequisite for optical binding[19,20,21,22], which can only occur if the scattered field from one particle strongly interacts with the other particles in the array, and vice-versa. In a 1D particle array, such as the one studied here, binding is possible because the optical fields propagate bidirectionally along the array

Methods

Results

Conclusion