Coherently tunable metalens tweezers for optofluidic particle routing

Abstract

Nanophotonic particle manipulation exploits unique light shaping capabilities of nanophotonic devices to trap, guide, rotate and propel particles in microfluidic channels. Recent introduction of metalens into microfluidics research demonstrates the new capability of using nanophotonics devices for far-field optical manipulation. In this work we demonstrate, via numerical simulation, the first tunable metalens tweezers that function under dual-beam illumination. The phase profile of the metalens is modulated by controlling the relative strength and phase of the two coherent incident light beams. As a result, the metalens creates a thin sheet of focus inside a microchannel. Changes to the illumination condition allow the focus to be swept across the microchannel, thereby producing a controllable and reconfigurable path for particle transport. Particle routing in a Y-branch junction, for both nano- and microparticles, is evaluated as an example functionality for the tunable metalens tweezers. This work shows that tunable far-field particle manipulation can be achieved using near-field nano-engineering and coherent control, opening a new way for the integration of nanophotonics and microfluidics.

A Review of Optical Tweezers with Metasurfaces

“…Replacing some traditional optical devices with metasurfaces can make systems smaller and more compact [21,22]. Integration is demonstrated in the fact that metasurfaces can be easily integrated with other metasurfaces and even other devices [23]. In addition, discrete local control of metasurfaces enables the integration of various optical device functions onto a single metasurface [15] and provide metasurfaces with advantages in generating structured beams [24].…”

Amplitude gradient-based metasurfaces for off-chip terahertz wavefront shaping

“…They enable a high level of control over electromagnetic waves across a broad frequency range that extends from gigahertz to the ultraviolet [1][2][3][4][5]. By imparting a judiciously designed change to the wavefront of these waves, metasurfaces can deflect a light beam towards a designated direction [6,7], and focus it into a diffraction-limited spot [8,9] or along a narrow line [10,11]. It can also convert a simple optical mode (e.g., a linearly polarized plane wave or a fundamental TE mode inside a waveguide) to a far more complicated mode, such as an optical vortex that carries orbital angular momentum (OAM) [12,13] and a hologram that transforms with wavelength [14,15].…”

Cubic-Phase Metasurface for Three-Dimensional Optical Manipulation

“…In the conventional configuration, an optical tweezer is driven by a focused Gaussian beam to generate optical gradient force to confine particles to only a few micrometers range due to short Rayleigh lengths [ 11 ]. To expand the freedom of stable operation from one dimension to three dimensions, optical manipulation systems based on two opposite laser beams [ 12 ], two crossed laser beams [ 13 ], and non-diffraction beams [ 14 , 15 , 16 , 17 ] have been demonstrated and applied in physical [ 10 , 18 , 19 , 20 , 21 ], chemical [ 22 , 23 ], and biological [ 6 , 7 , 8 , 9 ] sciences. Compared with Gaussian beams, non-diffraction and self-healing beams, such as the Bessel beam, Airy beam, and abrupt autofocusing beam, are able to maintain propagation properties up to long propagation distances [ 24 ].…”