Aside from optical pushing and trapping that have been implemented successfully, the transportation of objects backward to the source by the optical pulling forces (OPFs) has attracted tremendous attention, which was usually achieved by increasing the forward momentum of light. However, the limited momentum transfer between light and object greatly constrains the amplitudes of OPFs. Here, we present a mechanism to generate strong interactions between object and background through the bound states in the continuums, which can generate large OPFs without increasing the forward momentum of light.
View Article and Find Full Text PDFWe report an ingenious mechanism to obtain robust optical pulling force by a single plane wave via engineering the topology of light momentum in the background. The underlying physics is found to be the topological transition of the light momentum from a usual convex shape to a starlike concave shape in the carefully designed background, such as a photonic crystal structure. The principle and results reported here shed insightful concepts concerning optical pulling, and pave the way for a new class of advanced optical manipulation technique, with potential applications of drug delivery and cell sorting.
View Article and Find Full Text PDFMulti-functional optical manipulations, including optical trapping and transporting of subwavelength particles, are proposed using the Bloch modes in a dielectric photonic structure. We show that the Bloch modes in a periodic structure can generate a series of subwavelength trapping wells that are addressable by tuning the incident wavelength. This feature enables efficient optical trapping and transportation in a peristaltic way.
View Article and Find Full Text PDFWe achieve long-range and continuous optical pulling in a periodic photonic crystal background, which supports a unique Bloch mode with the self-collimation effect. Most interestingly, the pulling force reported here is mainly contributed by the intensity gradient force originating from the self-induced backaction of the object to the self-collimation mode. This force is sharply distinguished from the widely held conception of optical tractor beams based on the scattering force.
View Article and Find Full Text PDFOptical trapping of nano-objects (i.e., the nano-tweezers) has been investigated intensively.
View Article and Find Full Text PDFOptical evanescent wave in total internal reflection has been widely used in efficient optical manipulation, where the object is trapped by the intrinsic intensity gradient of the evanescent wave while transported by the scattering force along the orthogonal direction. Here, we propose a distinct optical manipulation scheme using the attenuated modes in subwavelength optical channels, where both the trapping and transportation forces are along the channel direction. We create such a mode in a sub-wavelength photonic crystal waveguide and quantitatively obtain the net pushing and pulling forces, which can overcome the Brownian motion within a critical length.
View Article and Find Full Text PDFOptical force exerted on a ring resonator, which can move freely in plane, is investigated using the finite-difference in time-domain method. In order to manipulate the ring resonator more flexibly, two assistant waveguides are introduced to form a microring resonator based add-drop device. Results show that a blue tuned source is more suitable for the manipulation of the ring, rather than the central resonant frequency as expected.
View Article and Find Full Text PDFBased on a hybrid discrete dipole approximation (DDA) and T-matrix method, a powerful dynamic simulation model is used to find plausible equilibrium orientation landscapes of micro- and nano-spheroids of varying size and aspect ratio. Orientation landscapes of spheroids are described in both linearly and circularly polarized Gaussian beams. It's demonstrated that the equilibrium orientations of the prolate and oblate spheroids have different performances.
View Article and Find Full Text PDFA design of ultra-short integrated polarization rotator (PR) with nonlinear and flat-tip tapers is demonstrated theoretically. Based on mode-evolution theory and three-dimensional (3D) finite-difference time-domain (FDTD) simulation, raised cosine profiled tapers are introduced and optimized in the transition region, which improve the polarized modes coupling and decrease the conversion length to 6 μm for the wavelength of 1.55 μm.
View Article and Find Full Text PDFThe polarization rotation of an optical slot structure from the vertical to the horizontal direction, or vice versa, is demonstrated theoretically within an ultrashort conversion length. Based on mode-evolution theory and three-dimensional finite-difference time-domain simulation, two parallel nonlinearly tapered crossings are introduced and optimized in the transition region, which efficiently decreases the conversion length from 11 to 5 μm for the wavelength of 1.55 μm in a silicon-on-isolator system.
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