Optical tweezing using tunable optical lattices along a few-mode silicon waveguide

Abstract

Fourteen years ago, optical lattices and holographic tweezers were considered as a revolution, allowing for trapping and manipulating multiple particles at the same time using laser light. Since then, near-field optical forces have aroused tremendous interest as they enable efficient trapping of a wide range of objects, from living cells to atoms, in integrated devices. Yet, handling at will multiple objects using a guided light beam remains a challenging task for current on-chip optical trapping techniques. We demonstrate here on-chip optical trapping of dielectric microbeads and bacteria using one-dimensional optical lattices created by near-field mode beating along a few-mode silicon nanophotonic waveguide. This approach allows not only for trapping large numbers of particles in periodic trap arrays with various geometries, but also for manipulating them via diverse transport and repositioning techniques. Near-field mode-beating optical lattices may be readily implemented in lab-on-a-chip devices, addressing numerous scientific fields ranging from bio-analysis to nanoparticle processing.

Perspective on light-induced transport of particles: from optical forces to phoretic motion

“…Besides dielectric objects, metallic nanoparticles [357,358] and living cells [359,360] can be also transported in the same way. If multiple co-propagating guided modes are excited simultaneously, by controlling either the polarization [358] or the position [361] of the incident beam coupled into the waveguide, larger metallic and dielectric objects can be repelled from the waveguide [358], propelled along its top or side surfaces [358,361], or held in place due to the interference of modes resulting in intensity gradients along the waveguide [361] (Fig. 36).…”

“…The behavior of particles trapped at the surface of the waveguide is also schematically depicted: 1. particles guided on top of the waveguide; 2. particles held in place at the sides of the waveguide; 3. particles held in place on top of the waveguide. Adapted with permission of Royal Society of Chemistry, from[361]; permission conveyed through Copyright Clearance Center, Inc. Sub-wavelength slot waveguide for the transport of nanoparticles or biomolecules. (a) Illustration of transport of two different sizes of nanoparticles.…”

Nanophotonics for bacterial detection and antimicrobial susceptibility testing

“…The main limitation of nanophotonic waveguides is their lower field enhancement compared with metallic nanostructures, which means that typically higher powers are required to achieve trapping. However, the trapping of bacteria is somewhat easier because of their volume, and the optical manipulation of bacteria with silicon waveguides has been successfully demonstrated with relatively low power (100 mW source power, corresponding to a few milliwatts coupled into the waveguides) [84].…”

Tunable optical assembly of subwavelength particles by a microfiber cavity

“…Compared with free-space propagation light, evanescent fields are capable of being concentrated beyond the diffraction limit [23][24][25][26][27][28], which not only enables a subwavelength spatial resolution for optical assembly, but also relaxes the trapping requirement on input light power. Various configurations of optical potential energy landscapes based on evanescent fields have been demonstrated, including plasmonic-nanostructure arrays [29,30], photonic crystal slabs [31,32], and on-chip optical waveguides [33][34][35]. However, these optical potential energy landscapes are typically limited to the predefined patterns and lacking in tunability, which significantly reduces the degrees of freedom of optical assembly manipulations.…”