Enhancing plasmonic trapping with a perfect radially polarized beam

Strong plasmonic focal spots, excited by radially polarized light on a smooth thin metallic film, have been widely applied to trap various micro-and nano-sized objects. However, the direct transmission part of the incident light leads to the scattering force exerted on trapped particles, which seriously affects the stability of the plasmonic trap.Here we employ a novel perfect radially polarized beam to solve this problem. Both theoretical and experimental results verify that such a beam could strongly suppress the directly transmitted light to reduce the piconewton scattering force, and an enhanced plasmonic trapping stiffness that is 2.6 times higher is achieved in experiments.The present work opens up new opportunities for a variety of research requiring the stable manipulations of particles.

All-optical manipulation of micrometer-sized metallic particles

Optical traps use focused laser beams to generate forces on targeted objects ranging in size from nanometers to micrometers. However, for their high coefficients of scattering and absorption, micrometer-sized metallic particles were deemed non-trappable in three dimensions using a single beam. This barrier is now removed. We demonstrate, both in theory and experiment, three-dimensional(3D) dynamic all-optical manipulations of micrometersized gold particles under high focusing conditions. The force of gravity is found to balance the positive axial optical force exerted on particles in an inverted optical tweezers system to form two trapping positions along the vertical direction. Both theoretical and experimental results confirm that stable 3D manipulations are achievable for these particles regardless of beam polarization and wavelength. The present work opens up new opportunities for a variety of in-depth research requiring metallic particles.

Multifunctional geometric phase optical element for high-efficiency full Stokes imaging polarimetry

Polarization imaging finds applications in many areas, such as photoelasticity, ellipsometry, and biomedical imaging. A compact, snapshot, and high-efficiency imaging polarimeter is highly desirable for many applications.Here, based on a single multifunctional geometric phase optical element(GPOE), a new method is proposed for high-efficiency snapshot imaging polarimetry. With tailored spatially varying orientation of each anisotropic unit cell, the GPOE works highly efficiently as both a spin sorter and a half-wave plate, enabling snapshot retrieving of a full Stokes vector of incident light. The designed GPOE is implemented in the form of liquid crystal fabricated with a photo-alignment technology, and its application in imaging polarimetry is experimentally demonstrated by retrieving full Stokes parameters of a cylinder vector beam. This method can also work in the form of plasmonic or dielectric metasurfaces, enabling ultra-compact polarization detection systems by monolithic integration with other devices such as metalenses.

High-speed Stokes vector receiver enabled by a spin-dependent optical grating

Stokes vector direct detection is a promising,cost-effective technology for short-distance communication applications.Here,we design and fabricate a spin-dependent liquid crystal grating to detect light polarization states.By separating the circular and linear components of incident light,the polarization states can be resolved with accuracy of up to 0.25°.We achieved Stokes vector direct detection of quadrature phase-shift keying(QPSK),8 PSK,and16-ary quadrature amplitude modulation signals with 32,16,and 16 GBd rates,respectively.We integrated the system,including the grating,photodetectors,and optical elements,on a miniaturized printed circuit board and demonstrated high-speed optical communications with 16 GBd rate QPSK signals.

Facilitated tip-enhanced Raman scattering by focused gap-plasmon hybridization

Tip-enhanced Raman scattering(TERS)spectroscopy is a nondestructive and label-free molecular detection approach that provides high sensitivity and nanoscale spatial resolution.Therefore,it has been used in a wide array of applications.We demonstrate a gap-plasmon hybridization facilitated by a bottom-illuminated TERS configuration.The gap-plasmon hybridization effect is first performed with the finite-difference time-domain method to optimize the parameters,and experiments are then conducted to calibrate the performance.The results demonstrate an enhancement factor of 1157 and a spatial resolution of 13.5 nm.The proposed configuration shows great potential in related surface imaging applications in various fields of research.