Applications In Optical Manipulation Research Articles

Optical vortex copier and regenerator in the Fourier domain

The generation and manipulation of optical vortices are of fundamental importance in a variety of promising applications. Here, we develop a nonlinear optical paradigm to implement self- and cross-convolution of optical vortex arrays, demonstrating the features of a vortex copier and regenerator. We use a phase-only spatial light modulator to prepare the 1064 nm invisible fundamental light to carry special optical vortex arrays and use a potassium titanyl phosphate crystal to perform type II second-harmonic generation in the Fourier domain to achieve 532 nm visible structured vortices. Based on pure cross-convolution, we succeed in copying arbitrary-order single vortices as well as their superposition states onto a prearranged array of fundamental Gaussian spots. Also, based on the simultaneous effect of self- and cross-convolutions, we can expand the initial vortex lattices to regenerate more vortices carrying various higher topological charges. Our presented method of realizing an optical vortex copier and regenerator could find direct applications in optical manipulation, optical imaging, optical communication, and quantum information processing with structured vortex arrays.

Optical force rectifiers based on PT-symmetric metasurfaces

We introduce here the concept of optical force rectifier based on parity-time symmetric metasurfaces. Directly linked to the properties of non-Hermitian systems engineered by balanced loss and gain constituents, we show that light can exert asymmetric pulling or pushing forces on metasurfaces depending on the direction of the impinging light. This generates a complete force rectification in the vicinity of the exceptional point. Our findings have the potential to spark the design of applications in optical manipulation where the forces, strictly speaking, act unidirectionally.

Propagation dynamics of ring Airy Gaussian beams with cosine modulated optical vortices

We numerically investigate the propagation properties of ring Airy Gaussian beams (RAGBs) with cosine modulated optical vortices (CMOV). In comparison to the common RAGBs without any modulation, the dynamic propagation of RAGBs with CMOV exhibits a unique feature: the rings of RAGBs with CMOV will gradually shrink into several main lobes with the increase of the propagation distance. The number of lobes and the peak intensity of each lobe are determined by the factors of cosine modulated function. By designing the initial phase, we can easily change the transversal location of the peak intensity. Our results may find potential applications in optical manipulations.

Vortex topographic microscopy for full-field reference-free imaging and testing.

Light vortices carry orbital angular momentum and have a variety of applications in optical manipulation, high-capacity communications or microscopy. Here we propose a new concept of full-field vortex topographic microscopy enabling a reference-free displacement and shape measurement of reflective samples. The sample surface is mapped by an array of light spots enabling quantitative reconstruction of the local depths from defocused wavefronts. Light from the spots is converted to a lattice of mutually uncorrelated double-helix point spread functions (PSFs) whose angular rotation enables depth estimation. The PSFs are created by self-interference of optical vortices that originate from the same wavefront and are shaped by a spiral phase mask (SPM). The method benefits from the isoplanatic PSFs whose shape and size remain unchanged under defocusing, ensuring high precision in a wide range of measured depths. The technique was tested using a microscope Nikon Eclipse E600 working with a micro-hole plate providing structured illumination and the SPM placed in the imaging path. The depth measurement was demonstrated in the range of 11 µm exceeding the depth of field of the microscope objective up to 19 times. Throughout this range, the surface depth was mapped with the precision better than 30 nm at the lateral positions given with the precision better than 10 nm. Application potential of the method was demonstrated by profiling the top surface of a bearing ball and reconstructing the three-dimensional relief of a reflection phase grating.

Focusing properties of radially polarized helico-conical Lorentz-Gauss beam

Helico-conical wavefront modulation affects focusing properties and plays an important role in many optical systems. Radially polarized Lorentz-Gauss beams were modulated with helico-conical wavefront and their focusing properties were investigated by vector diffraction theory. Results show that focusing properties may be alerted considerably by helico-conical parameters, and some novel focal patterns appear. The focal patterns turn on spiral inteinsity curves, and the effect of numerical aperture is weaker than that of helico-conical parameters. Some optical gradient force distributions are also calculated to show that focusing radially polarized helico-conical Lorentz-Gauss beam may find wide applications in optical manipulation.

Data information transfer using complex optical fields: a review and perspective (Invited Paper)

Tailored complex optical fields, may find applications in optical manipulation, imaging, microscopy, quantum information processing, and optical communications. Here, we focus on data information transfer for optical communications using complex optical fields. We review recent research progress in complex optical field modulation, multiplexing, and multicasting for data information transfer on different platforms of waveguides, free space, and fiber. Challenges and perspectives are also discussed.

Generation of non-uniformly correlated stochastic electromagnetic beams

Until now, there have been many reports concerning the generation and propagation of partially coherent beams due to their less influencing ability in turbulent atmosphere and random media. Of particular interest, a Gaussian-Schell model beam has been widely chosen as a special example of partially coherent beam, since its spatial coherence degree is dependent on position only through the difference between the two position vectors. In the scalar domain, many coherent models have been well studied such as Gaussian and multi-Gaussian Schell-model sources, Bessel-Gaussian and Laguerre-Gaussian Schell-model sources and so on. Based on the theory for devising genuine cross-spectral density matrices for a stochastic electromagnetic beam, several scalar models have been also extended to the electromagnetic domain. In recent years, the propagation of partially coherent beams with spatially varying and non-uniform correlations has become a hot topic, because of their interesting characteristics such as locally sharpened and laterally shifted intensity maxima. In one of our previous studies, we have experimentally investigated the generation of non-uniformly correlated partially coherent beams. However, to the best of our knowledge, so far, there has been no investigation on the generation of non-uniformly correlated stochastic electromagnetic beams. In this paper, we theoretically and experimentally investigate the generation of non-uniformly correlated stochastic electromagnetic beams. Based on the relation between phase correlation and optical coherence, we investigate the 22 cross-spectral density matrix and the coherence distribution of the non-uniformly correlated stochastic electromagnetic beam we generated. It is shown that the coherence degree between two points in the generated beam depends not only on the distance between them, but also on the distances between the points and the center of the beam. In experiment, we use the Matlab rand function to generate a random phase pattern with uniform distribution. The modulation magnitudes of different positions are different and follow an inverse Gaussian distribution in position. Dynamic phase patterns are created from a series of random grey-scale images. Two phase-only liquid crystal spatial light modulators are employed to display computer-generated dynamic phase patterns and modulate the two orthogonally polarized components of the incident coherent light, respectively, and generate a stochastic electromagnetic beam. We measure the correlation distribution of the generated beam in Young's two-pinhole experiment. It is shown that the experimental observations are in agreement with our theoretical analyses. Other kinds of non-uniformly correlated stochastic electromagnetic beams can also be obtained by this approach. Non-uniformly correlated stochastic electromagnetic beams may have some applications in optical manipulation and free-space optical communication.

Hybrid Refractive–Diffractive Optical Vortex Microlens

We report a novel hybrid refractive-diffractive microlens combined with spiral phase for the generation of optical vortex, which is fabricated via femtosecond laser direct writing technology. The unique optical performance of focusing capability is demonstrated. At the focus position, the hollow focus with different integer topological charges is investigated. Moreover, experimental results are supported by finite-element calculation. The novel microlens generating an optical vortex will fulfill important applications in optical manipulation, multistate information encoding, quantum communication, and computation, particularly in the compaction, integration, and simplification of optical vortex generation system.

Investigating the use of a hybrid plasmonic–photonic nanoresonator for optical trapping using finite-difference time-domain method

We investigate the use of a hybrid nanoresonator comprising a photonic crystal (PhC) cavity coupled to a plasmonic bowtie nanoantenna (BNA) for the optical trapping of nanoparticles in water. Using finite-difference time-domain simulations, we show that this structure can confine light to an extremely small volume of $${\sim } 30,000\, \hbox {nm} ^3 ({\sim } 30$$ zl) in the BNA gap whilst maintaining a high quality factor (5400–7700). The optical intensity inside the BNA gap is enhanced by a factor larger than 40 compared to when the BNA is not present above the PhC cavity. Such a device has potential applications in optical manipulation, creating high precision optical traps with an intensity gradient over a distance much smaller than the diffraction limit, potentially allowing objects to be confined to much smaller volumes and making it ideal for optical trapping of Rayleigh particles (particles much smaller than the wavelength of light).

Generation of photonic orbital angular momentum superposition states using vortex beam emitters with superimposed gratings

An integrated approach to produce photonic orbital angular momentum (OAM) superposition states with arbitrary OAM spectrum has been demonstrated. Superposition states between two vector OAM modes have been achieved by integrating a superimposed angular grating in one silicon micro-ring resonator, with each mode having near equal weight. The topological charge difference between the two compositional OAM modes is determined by the difference between the numbers of elements in the two original gratings being superimposed, while the absolute values of the topological charge can be changed synchronously by switching WGM resonant wavelengths. This novel approach provides a scalable and flexible source for the OAM-based quantum information and optical manipulation applications.

Direct Measurement of Optical Force Induced by Near-Field Plasmonic Cavity Using Dynamic Mode AFM.

Plasmonic nanostructures have attracted much attention in recent years because of their potential applications in optical manipulation through near-field enhancement. Continuing experimental efforts have been made to develop accurate techniques to directly measure the near-field optical force induced by the plasmonic nanostructures in the visible frequency range. In this work, we report a new application of dynamic mode atomic force microscopy (DM-AFM) in the measurement of the enhanced optical force acting on a nano-structured plasmonic resonant cavity. The plasmonic cavity is made of an upper gold-coated glass sphere and a lower quartz substrate patterned with an array of subwavelength gold disks. In the near-field when the sphere is positioned close to the disk array, plasmonic resonance is excited in the cavity and the induced force by a 1550 nm infrared laser is found to be increased by an order of magnitude compared with the photon pressure generated by the same laser light. The experiment demonstrates that DM-AFM is a powerful tool for the study of light induced forces and their enhancement in plasmonic nanostructures.

Elegant Gaussian beams for enhanced optical manipulation

Generation of micro- and nanostructured complex light beams attains increasing impact in photonics and laser applications. In this contribution, we demonstrate the implementation and experimental realization of the relatively unknown, but highly versatile class of complex-valued Elegant Hermite- and Laguerre-Gaussian beams. These beams create higher trapping forces compared to standard Gaussian light fields due to their propagation changing properties. We demonstrate optical trapping and alignment of complex functional particles as nanocontainers with standard and Elegant Gaussian light beams. Elegant Gaussian beams will inspire manifold applications in optical manipulation, direct laser writing, or microscopy, where the design of the point-spread function is relevant.

Investigating the focus shaping of the TEM11* beam with radial varying polarization

In this article, based on vector diffraction theory the focusing properties of double ring shaped higher order Laguerre–Gauss beam with radial varying polarization are investigated numerically. The numerical simulations show that the evolution of some interesting focal spot, focal split and focal patterns in the focal region by changing polarization rotation angle under tight focusing through the high NA lens. It is also shown that a subwavelength focal hole with a quite long depth of focus, multiple focal holes are achieved near the focus, when tuning β (is the ratio of the pupil radius to the beam waist) in the focal plane for different modes under tight focusing through the high NA lens. We found that when tuning, beam parameter or the polarization rotation angle of the incident beam, it is possible to generate some interesting novel focal patterns, including multiple intensity rings, dark hollow focus and cylindrical crust focus. Such kind of beams plays an important role in optical trapping, laser cutting and optical manipulation applications.

Optical torque from enhanced scattering by multipolar plasmonic resonance

AbstractWe present a theoretical study of the optical angular momentum transfer from a circularly polarized plane wave to thin metal nanoparticles of different rotational symmetries. While absorption has been regarded as the predominant mechanism of torque generation on the nanoscale, we demonstrate numerically how the contribution from scattering can be enhanced by using multipolar plasmon resonance. The multipolar modes in non-circular particles can convert the angular momentum carried by the scattered field and thereby produce scattering-dominant optical torque, while a circularly symmetric particle cannot. Our results show that the optical torque induced by resonant scattering can contribute to 80% of the total optical torque in gold particles. This scattering-dominant torque generation is extremely mode-specific, and deserves to be distinguished from the absorption-dominant mechanism. Our findings might have applications in optical manipulation on the nanoscale as well as new designs in plasmonics and metamaterials.

Engineering light-matter interaction for emerging optical manipulation applications

AbstractIn this review, we explore recent trends in optical micromanipulation by engineering light-matter interaction and controlling the mechanical effects of optical fields. One central theme is exploring the rich phenomena beyond the now established precision measurements based on trapping micro beads with tightly focused beams. Novel synthesized beams, exploiting the linear and angular momentum of light, open new possibilities in optical trapping and micromanipulation. Similarly, novel structures are promising to enable new optical micromanipulation modalities. Moreover, an overview of the amazing features of the optics of tractor beams and backward-directed energy fluxes will be presented. Recently the so-called effect of negative propagation of the beams (existence of the backward energy fluxes) has been confirmed for X-waves and Airy beams. In the review, we will also discuss the negative pulling force of structured beams and negative energy fluxes in the vicinity of fibers. The effect is achieved due to the interaction of multipoles or, in another interpretation, the momentum conservation. Both backward-directed Poynting vector and backward optical forces are counter-intuitive and give an insight into new physics and technologies. Exploiting the degrees of freedom in synthesizing novel beams and designed microstructures offer attractive prospects for emerging optical manipulation applications.

Shaping of focal field with controllable amplitude, phase, and polarization

We propose a method for configuring the distribution of amplitude, phase, and polarization in the focal region of vector beams. The polarization and phase of incident beam is spatially tailored so that it can produce a focal field that has elaborately prescribed shapes. Our work focuses on the design of a special focus structure with two oval rings, wherein a phase gradient and polarization gradient exist in the inner and outer rings, respectively. The incident light yielding the desired focal field is determined based on an iterative scheme involving vectorial diffraction calculations and fast Fourier transforms. Simulations and experiments demonstrate the generation of a focal field with phase and polarization gradients, which may find applications in optical manipulation.

Experimental generation of nonuniformly correlated partially coherent light beams

We report the experimental realization of nonuniformly correlated partially coherent light (NUCPCL) beams by passing laser beams through a phase-only spatial light modulator. The characteristics of NUCPCL beams whose coherence is of Gaussian distribution as well as inverse Gaussian distribution are studied theoretically and experimentally. It is shown that the experimental observations are in agreement with our theoretical analysis. NUCPCL beams may have some applications in optical manipulation.

Study on polarization effect of azimuthally polarized LG beam in high NA Lens system

Based on vector diffraction theory, the intensity distributions of azimuthally polarized double-ring-shaped higher order beams near the focus are calculated numerically. It is shown that a subwavelength focal hole with a quite long depth of focus, multiple focal holes are achieved near the focus, when tuning β (is the ratio of the pupil radius to the beam waist) in the focal plane for different modes under tight focusing through high NA lens. Such kind of beams plays an important role in optical trapping, laser cutting and optical manipulation applications.

Scattering of an axicon-generated Bessel beam by a sphere

The scattering of an axicon-generated Bessel beam (AGBB) by a sphere is investigated. An analytical formula for the calculation of Beam Shape Coefficients (BSCs) of an AGBB is first derived according to the Integral Localized Approximation (ILA). After the verification of BSCs by the comparison of the reconstructed field using BSCs with the original field obtained from the definition, the far-field scattered intensity is evaluated, and the rainbow produced by AGBB is also studied. The effect of angle α0 on the far-field scattered intensity and the first rainbow is analyzed in detail. Such investigation could provide a useful tool for the research on radiation forces and torques, which is important in optical tweezers and the related optical manipulation applications.

Generation of enhanced evanescent Bessel beam using band-edge resonance

A method for generating enhanced evanescent Bessel beam is reported. When a radially polarized beam is strongly focused onto the last interface of one-dimensional photonic band gap structure, enhanced evanescent J0 type Bessel beam can be generated via the band-edge resonance. Similarly, enhanced evanescent J1 type Bessel beam can be created by reversing the multilayer structure under azimuthally polarized illumination. These enhanced evanescent Bessel fields may have important applications in optical manipulations of nanoparticles.