Plasmonic nanotweezers employing metallic nanoantennas provide a powerful tool for trapping nanoscale particles, but the strong heating effect resulting from light absorption limits widespread applications. Here, we propose an alldielectric nanotweezer harnessing quasi-bound states in the continuum (quasi-BICs) to enable the trapping of nanoscale objects with low laser power and a negligible heating effect. The quasi-BIC system provides very high electromagnetic field intensity enhancement that is an order of magnitude higher than plasmonic systems as well as high-quality-factor resonances comparable to photonic crystal cavities. Furthermore, the quasi-BIC metasurface tweezer array provides multiple optical hotspots with high field confinement and enhancement, thereby generating multiple trapping sites for the high-throughput trapping of nanometer-scale objects. By purposefully truncating the tips of the constituent elliptical nanoantennas in the quasi-BIC system to leverage the asymmetric field distribution, we demonstrate that the optical gradient forces can be further enhanced by a factor of 1.32 in comparison to the intact elliptical nanoantenna, which has attractive potential in subwavelength particle trapping applications. In addition, we show that trapped particles can improve the resonance mode of the cavity rather than suppress it in a symmetry-broken system, which in turn enhances the trapping process. Our study paves the way for applying quasi-BIC systems to low-power particle trapping and sensing applications and provides a new mechanism to harness the self-induced back-action.
Low-power trapping of nanoscale objects can be achieved by using the enhanced fields near plasmonic nanoantennas. Unfortunately, in this approach the trap site is limited to the position of the plasmonic hotspots and continuous dynamic manipulation is not feasible. Here, we report a low-frequency electrothermoplasmonic tweezer (LFET) that provides low-power, high-stability and continuous dynamic manipulation of a single nanodiamond. LFET harnesses the combined action of the laser illumination of a plasmonic nanopillar antenna array and lowfrequency alternating current (ac) electric field to establish an electrohydrodynamic potential capable of the stable trapping and dynamic manipulation of single nanodiamonds. We experimentally demonstrate the fast transport, trapping, and dynamic manipulation of a single nanodiamond using a low-frequency ac field below 5 kHz and low-laser power of 1 mW. This nanotweezer platform for nanodiamond manipulation holds promise for the scalable assembly of single photon sources for quantum information processing and low noise quantum sensors.
A near-eye visor is one of the most vital components in a head-mounted display. Currently, freeform optics and waveguides are used to design near-eye visors, but these structures are complex and their field of view is limited when the visor is placed near the eye. In this paper, we propose a flat, freeform near-eye visor which uses a subwavelength patterned metasurface reflector. The visor design imparts a spatial phase profile on a projected display pattern and can be implemented using a micron-scale thick metasurface. As the resulting metaform visor relies on diffraction, it can preserve a large field of view (77.3° both horizontally and vertically) when placed only 2.5 cm away from the eye. We simulate the metasurface visor to estimate the modulation transfer function, and find that the projected image quality is sufficiently high for human vision. While the design of the metasurface is initially performed via ray optics, using full-wave finite-difference time-domain simulation we validate a scaled version of our visor design.
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