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The selective control and manipulation of nanoparticles require developing and researching new methods for designing optical tweeters, mainly based on a photonic hooks (PHs) effect. This paper first proposes a tunable PH in which a structured beam illuminates an anisotropic cutting liquid crystal microcylinder based on the Finite-DifferenceTime-Domain (FDTD) method. The PHs generated by plane wave, Gaussian, and Bessel beam are analyzed and compared. The impact of beams and LC particle parameters on the PHs are discussed. Where the influence of the extraordinary refractive index ( n e ) on PHs is emphasized. Our results reveal that introducing birefringence can change the bending direction of PH. Besides, the maximum intensity of the PHs increases as n e increases regardless of the beam type. The PH generated by a plane wave has a higher maximum intensity and smaller FWHM than that generated by the Gaussian and Bessel beams. The smallest FWHM and maximum intensity of the PHs generated by the Gaussian falls between that generated by the plane wave and the Bessel beam. The PH generated by a Bessel beam has the minor maximum intensity and the largest FWHM. Still, it exceeds the diffraction limit and exhibits bending twice due to its self-recovery property. This paper provides a new way to modulate PH. This work offers novel theoretical models and the degree of freedom for the design of PHs, which is beneficial for the selective manipulation of nanoparticles. It has promising applications in Mesotronics and biomedicine. [ABSTRACT FROM AUTHOR]

The selective control and manipulation of nanoparticles require developing and researching new methods for designing optical tweeters, mainly based on a photonic hooks (PHs) effect. This paper first proposes a tunable PH in which a structured beam illuminates an anisotropic cutting liquid crystal microcylinder based on the Finite-DifferenceTime-Domain (FDTD) method. The PHs generated by plane wave, Gaussian, and Bessel beam are analyzed and compared. The impact of beams and LC particle parameters on the PHs are discussed. Where the influence of the extraordinary refractive index (ne) on PHs is emphasized. Our results reveal that introducing birefringence can change the bending direction of PH. Besides, the maximum intensity of the PHs increases as ne increases regardless of the beam type. The PH generated by a plane wave has a higher maximum intensity and smaller FWHM than that generated by the Gaussian and Bessel beams. The smallest FWHM and maximum intensity of the PHs generated by the Gaussian falls between that generated by the plane wave and the Bessel beam. The PH generated by a Bessel beam has the minor maximum intensity and the largest FWHM. Still, it exceeds the diffraction limit and exhibits bending twice due to its self-recovery property. This paper provides a new way to modulate PH. This work offers novel theoretical models and the degree of freedom for the design of PHs, which is beneficial for the selective manipulation of nanoparticles. It has promising applications in Mesotronics and biomedicine.

In this paper, we demonstrate a novel photonic hook being initiated using an air–liquid interface (ALI). This bent light focus is produced by immersing a dielectric micro-cylinder partially at the edge of a thin liquid film whose thickness is smaller than the diameter of the micro-cylinder. Unlike the well-known properties of normal near-field focuses, this photonic hook propagates horizontally in the liquid along the ALI at specific depths and does not require the material processing of microscopic particles or the modulation of light irradiation for initiation. A morphological analysis indicates that the contrast in the refractive indexes of the ALI causes this phenomenon at the shadow end of the micro-cylinder with a transverse dimension smaller than the diffraction limit. Compared to previously discovered photonic hooks, the unique setup of this photonic hook can generate a force field that enables optical trapping in the region slightly beneath the ALI, and the related optical pressures have been simulated. [ABSTRACT FROM AUTHOR]

This paper pays attention to the broader interest of freezing water droplets in mesotronics, particularly to their use as a new all-optical device platform. Here, we show that a freezing mesoscale water droplet with a low Bond number can behave as fully biocompatible natural microlense to form a photonic hook for application in a tunable temperature-controlled optical switch. We first introduced and demonstrated the basic concepts of an optical switch without changes in the wavelength of illumination of a particle or any moving parts being involved. The principle of the operation of the switch is based on the temperature-induced phase change inside the water droplet's refractive index. The simulation results show that the optical isolation of switched channels for an optical switch with linear dimensions of about 15 λ3 based on a freezing water droplet can reach 10 dB in the process of temperature variation at a fixed wavelength. The use of freezing mesoscale droplets acting as a time-domain photonic hook generator open an intriguing route for optical switching in multifunctional green electronics tools for sensing, integrated optics and optical computers. [ABSTRACT FROM AUTHOR]

Experimental limitations such as design complexity and low optical throughput have prevented photonic nanojet (PNJ) and photonic hook (PH) measurements from demonstrating and characterizing the implementation of narrow intense electromagnetic beams generated from dielectric microelements with circular symmetry. Near-fields optical microscopy can mitigate these limitations and still present a capability of detecting a highly localized electromagnetic beam for applications in step-index media. Here we model a localized PNJ and PH formation in step-index media. We show that despite negligible refractive index contrast between the water ( n w a t e r = 1.33 ) and silica microcylinder (∼1.1), a formation of PNJ and PH is observed with equivalent performance compared to that of silica microcylinder embedded in air ( n a i r = 1 ). This model features a practical fiber source and silica microcylinder as an auxiliary structure. Simultaneously, we performed experimental characterization of a photonic nanojet generated from an optical fiber and studied the resulting near-fields. Our electromagnetic simulation results are in good agreement with the experimental ones, demonstrating a full width at half maximum (FHWM) with a relative error of 0.64%. This system will make fiber-based nanojet realization and characterization accessible and practical for optics and laser engineering applications, super-resolution imaging, and nanolithography. [ABSTRACT FROM AUTHOR]

In this study, we propose a novel design of triangular mesoscale Janus prisms for the generation of the long photonic hook. Numerical simulations based on the finite-difference time-domain method are used to examine the formation mechanism of the photonic hook. The electric intensity distributions near the micro-prisms are calculated for operation at different refractive indices and spaces of the two triangular micro-prisms. The asymmetric vortices of intensity distributions result in a long photonic hook with a large bending angle. The length and the bending angle of the photonic hook are efficiently modulated by changing the space between the two triangular micro-prisms. Moreover, the narrow width of the photonic hook is achieved beyond the diffraction limit. The triangular Janus micro-prisms have high potential for practical applications in optical tweezers, nanoparticle sorting and manipulation and photonic circuits. [ABSTRACT FROM AUTHOR]

• We firstly present two kinds of methods for the photonic hook generation by a dielectric micro-cylinder illuminated under an electric dipole using the finite element method. • A point dipole source, placed near the surface of the cylinder the propagation directions of the wave fronts illuminating the surface of the mesoscale dielectric cylinder are not parallel to each other, in contrast to classical plane-wave illumination. • Through changing the position and orientation of the point dipole, which can be considered as additional degrees of freedom to control the characteristics of the photonic hook, one can obtain the asymmetric illumination to produce the photonic hook. In this paper, we numerically investigate a photonic hook (PH) generated by a dielectric micro-cylinder illuminated under an electric dipole using the finite element method. At first, we show the properties of the photonic nanojet (PNJ) produced by the micro-cylinder under an electric dipole. Then, we find that a PH can be obtained when the electric dipole is moved at a certain distance along the direction perpendicular to the center line of the cylinder. Considering the rotation symmetry of the model, we firstly present that a PH can be generated by changing the orientation of the electric dipole. And the power flow of the PHs produced by different orientated dipoles are studied. Finally, the PHs properties affected by the gap distance between the micro-cylinder and the electric dipole and the refractive index of the micro-cylinder are investigated. Our results provide a method to generate a PH under a dipole illumination. And it may have potential applications in the quantum dot detection and microsphere super-resolution. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a novel photonic hook being initiated using an air–liquid interface (ALI). This bent light focus is produced by immersing a dielectric micro-cylinder partially at the edge of a thin liquid film whose thickness is smaller than the diameter of the micro-cylinder. Unlike the well-known properties of normal near-field focuses, this photonic hook propagates horizontally in the liquid along the ALI at specific depths and does not require the material processing of microscopic particles or the modulation of light irradiation for initiation. A morphological analysis indicates that the contrast in the refractive indexes of the ALI causes this phenomenon at the shadow end of the micro-cylinder with a transverse dimension smaller than the diffraction limit. Compared to previously discovered photonic hooks, the unique setup of this photonic hook can generate a force field that enables optical trapping in the region slightly beneath the ALI, and the related optical pressures have been simulated.

We propose and discuss main properties of a new concept of an all-optical dielectric two-channel wavelength-selective switch based on the photonic hook effect. A prototype of such a de-vice based on dielectric microstructures with broken symmetry of both geometric shape and optical properties without the use of micromechanical devices or nonlinear materials is considered. Due to the unique property of the photonic hook to change its curvature depending on the wavelength of illuminating light, this switch is a promising candidate for the implementation of optical switching in modern optoelectronics and miniature devices "on a chip". Based on numerical FDTD simulations, it is shown that the optical isolation of switched channels for a switch with linear dimensions of about (6 * "lambda")3 based on a Janus particle can reach about 18-20 dB in the wavelength range of 1.5 – 1.9 microns.

Optical switches are key elements in modern network communications. We present the results of the experimental verification of a new theoretical concept proposed earlier for a full-optical wavelength-selective dual-channel switch based on the photonic hook effect, which is free from using any micro-mechanical devices or nonlinear materials. A large-scale laboratory prototype of such a device based on an off-axis Wood zone plate is considered, and its main parameters in the millimeter wavelength range are investigated. On the basis of the experiments, we show that the optical isolation of switched channels for a switch based on an off-axis zone plate can achieve 15 dB at a frequency difference of 25 GHz in a frequency range of 93 to 136 GHz. Given the scaling, these results can be transferred to another range, including the optical one. [ABSTRACT FROM AUTHOR]

Photonic hook (PH) is a new type of non-evanescent light beam with subwavelength curved structures. It has shown promising applications in super-resolution imaging and has the potential to be used in micromachining, optical trapping, etc. PHs are generally produced by illuminating mesoscale asymmetric particles with optical plane waves. In this work, we used the finite-difference time-domain (FDTD) method to investigate the PH phenomenon under point-source illumination. We found that the PHs can be effectively generated from point-source illuminated patchy particles. By changing the background refractive index, particle diameters and the position and coverage ratio of Ag patches, the characteristics of the PHs can be effectively tuned. Moreover, the structure of the intensity distribution of the light field generated from small and large particles can have an opposite bending direction due to the near-field light-matter interaction. [ABSTRACT FROM AUTHOR]

Owing to its crooked trajectory and small full width at half-maximum, photonic hook (PH) has attracted wide attention since its inception and experimental confirmation. However, the present generation and regulation of PH are mostly dependent on the breaking of the symmetry of the system composed of the incident light and the regular structure particles, which inevitably limits the research of PH. In this work, the PH of the irregular particles is demonstrated with the help of a structure-constrained function (SCF). By varying the coefficients of the function, characteristic parameters of the PH, such as the bending angle, the effective length and the bending direction, can be effectively modulated. Meanwhile, high-quality PHs with a bending angle of up to 46° and an effective length of up to 11.90λ, as well as PHs with three bends, can be obtained using this method. The formation mechanism of the PH is revealed by simulating the distribution of the field intensity with the finite element method and analyzing with ray optics. This is the first time that we introduce a function into the investigation of PH, paving a new way for a more interesting exploration of PH. [ABSTRACT FROM AUTHOR]

This paper pays attention to the broader interest of freezing water droplets in mesotronics, particularly to their use as a new all-optical device platform. Here, we show that a freezing mesoscale water droplet with a low Bond number can behave as fully biocompatible natural microlense to form a photonic hook for application in a tunable temperature-controlled optical switch. We first introduced and demonstrated the basic concepts of an optical switch without changes in the wavelength of illumination of a particle or any moving parts being involved. The principle of the operation of the switch is based on the temperature-induced phase change inside the water droplet’s refractive index. The simulation results show that the optical isolation of switched channels for an optical switch with linear dimensions of about 15 λ3 based on a freezing water droplet can reach 10 dB in the process of temperature variation at a fixed wavelength. The use of freezing mesoscale droplets acting as a time-domain photonic hook generator open an intriguing route for optical switching in multifunctional green electronics tools for sensing, integrated optics and optical computers.

• We produce an optical fiber-based photonic hook for achieving selective particle manipulation in a lab-on-tip platform. • We experimentally demonstrate selectively manipulating and sorting biological cells. • The fiber tip with broken symmetry has emerged as a "lab-on-tip" compact ready-to-use flexible device for applications. Optical tweezers and trapping technologies have a crucial impact on scientific research by precisely manipulating mesoscale objects at wavelength scales. The development of simple fiber-based optical tweezers foreseeing sorting and manipulation of a single cell has been firstly encouraged by biomedical requirements. The ability to manipulate mesoscale objects with high flexibility and precision is essential for a wide class of different fields. The ability to precisely arrange cells into desired structures is important for numerous biomedical and physical applications. This study experimentally reports for the first time a simple and low-cost strategy to produce an optical fiber-based photonic hook for achieving new unprecedented functionalities to selective particle manipulation in a lab-on-tip platform. We show perspectives opened by combining the fields of structured light in the form of the photonic hook and optical manipulation method. This enables new applications for optical trapping setups based on structured fields in the form of the photonic hook produced by an optical fiber tip with broken symmetry, where it becomes possible to manipulate and sort cells selectively. [ABSTRACT FROM AUTHOR]

Experimental limitations such as design complexity and low optical throughput have prevented photonic nanojet (PNJ) and photonic hook (PH) measurements from demonstrating and characterizing the implementation of narrow intense electromagnetic beams generated from dielectric microelements with circular symmetry. Near-fields optical microscopy can mitigate these limitations and still present a capability of detecting a highly localized electromagnetic beam for applications in step-index media. Here we model a localized PNJ and PH formation in step-index media. We show that despite negligible refractive index contrast between the water (nwater=1.33) and silica microcylinder (∼1.1), a formation of PNJ and PH is observed with equivalent performance compared to that of silica microcylinder embedded in air (nair=1). This model features a practical fiber source and silica microcylinder as an auxiliary structure. Simultaneously, we performed experimental characterization of a photonic nanojet generated from an optical fiber and studied the resulting near-fields. Our electromagnetic simulation results are in good agreement with the experimental ones, demonstrating a full width at half maximum (FHWM) with a relative error of 0.64%. This system will make fiber-based nanojet realization and characterization accessible and practical for optics and laser engineering applications, super-resolution imaging, and nanolithography.

Photonic hook is a high-intensity, bent light focus with a proportional curvature to the wavelength of the incident light. Based on this unique light-bending phenomenon, a novel near-field photonic switch by means of a right-trapezoid dielectric Janus particle-lens embedded in the core of a planar waveguide is proposed for switching the photonic signals at two common optical communication wavelengths, 1310 nm and 1550 nm, by using numerical simulations. The signals at these two wavelengths can be guided to different routes according to their oppositely bent photonic hooks to realise wavelength selective switching. The switching mechanism is analysed by an in-house developed three-dimensional (3D) Poynting vector visualisation technology. It demonstrates that the 3D distribution and number of Poynting vector vortexes produced by the particle highly affect the shapes and bending directions of the photonic hooks causing the near-field switching, and multiple independent high-magnitude areas matched by the regional Poynting vector streamlines can form these photonic hooks. The corresponding mechanism can only be represented by 3D Poynting vector distributions and is being reported for the first time. [ABSTRACT FROM AUTHOR]

Recently, two special photonic jets, photonic hooks and twin photonic jets, have been proposed to deal with complex conditions in nanoscale manipulation. Photonic hooks are generated by a single light plane wave and an asymmetric microparticle, while the twin photonic jets are produced by two incident light beams. In this letter, we presented and demonstrated a method to combine photonic hooks and twin photonic jets. A single light plane wave and a symmetric microparticle, twin-ellipse microcylinder, are used in this research. The curvature degree, length and maximum E2 field enhancement of twin photonic hooks are varied significantly, with the change of refractive indices and shape of twin-ellipse microcylinder. And a liquid-immersed core-shell is built to achieve a flexible tunability.

In this study, we propose a novel design of triangular mesoscale Janus prisms for the generation of the long photonic hook. Numerical simulations based on the finite-difference time-domain method are used to examine the formation mechanism of the photonic hook. The electric intensity distributions near the micro-prisms are calculated for operation at different refractive indices and spaces of the two triangular micro-prisms. The asymmetric vortices of intensity distributions result in a long photonic hook with a large bending angle. The length and the bending angle of the photonic hook are efficiently modulated by changing the space between the two triangular micro-prisms. Moreover, the narrow width of the photonic hook is achieved beyond the diffraction limit. The triangular Janus micro-prisms have high potential for practical applications in optical tweezers, nanoparticle sorting and manipulation and photonic circuits.

Optical switches are key elements in modern network communications. We present the results of the experimental verification of a new theoretical concept proposed earlier for a full-optical wavelength-selective dual-channel switch based on the photonic hook effect, which is free from using any micro-mechanical devices or nonlinear materials. A large-scale laboratory prototype of such a device based on an off-axis Wood zone plate is considered, and its main parameters in the millimeter wavelength range are investigated. On the basis of the experiments, we show that the optical isolation of switched channels for a switch based on an off-axis zone plate can achieve 15 dB at a frequency difference of 25 GHz in a frequency range of 93 to 136 GHz. Given the scaling, these results can be transferred to another range, including the optical one.

Photonic hook (PH) is a new type of non-evanescent light beam with subwavelength curved structures. It has shown promising applications in super-resolution imaging and has the potential to be used in micromachining, optical trapping, etc. PHs are generally produced by illuminating mesoscale asymmetric particles with optical plane waves. In this work, we used the finite-difference time-domain (FDTD) method to investigate the PH phenomenon under point-source illumination. We found that the PHs can be effectively generated from point-source illuminated patchy particles. By changing the background refractive index, particle diameters and the position and coverage ratio of Ag patches, the characteristics of the PHs can be effectively tuned. Moreover, the structure of the intensity distribution of the light field generated from small and large particles can have an opposite bending direction due to the near-field light-matter interaction.

Photonic hook (PH) is a new type of curved subwavelength light beam generated at the shadow side of asymmetrical particles, which has aroused widespread interest since its numerical simulation implementation and experimental confirmation. However, the generation of PH is strongly dependent on particles with complex structures that are difficult to process and there is no comprehensive evaluation criterion for the properties of PH. In this work, a simple bilayer eccentric microelliptic column which is easy to process is proposed, and the length and bending angle of the PH can be tuned by varying the eccentricity, the refractive index of material, the ellipsoidal deflection ratio, and the angle of incident of light. In addition to a single property of PH, such as bending angle or effective length, its integrated performance has been fully analyzed for the first time with the aid of a quality factor Q PH. And Q PH can be used as a parameter to measure the comprehensive properties of PH. Meanwhile, high-quality PH can be attained by referring Q PH with curved angle up to 34°and effective length up to 16.5 λ , as well as PH with the value of Q PH up to 108. The obtained results can be used to synthetically evaluate the properties of PH, and they are conducive to achieving tunable PH with simple structures in future research. • The eccentric ellipsoidal column was first proposed for the generation of PH. • Free regulation of PH can be achieved effectively with bending angle up to 34°and effective length up to 16.5 λ. • Introducing and redefining the quality factor of photonic nanojet (PNJ) can realize the comprehensive evaluation of PH quantitatively. [ABSTRACT FROM AUTHOR]

Owing to its crooked trajectory and small full width at half-maximum, photonic hook (PH) has attracted wide attention since its inception and experimental confirmation. However, the present generation and regulation of PH are mostly dependent on the breaking of the symmetry of the system composed of the incident light and the regular structure particles, which inevitably limits the research of PH. In this work, the PH of the irregular particles is demonstrated with the help of a structure-constrained function (SCF). By varying the coefficients of the function, characteristic parameters of the PH, such as the bending angle, the effective length and the bending direction, can be effectively modulated. Meanwhile, high-quality PHs with a bending angle of up to 46∘ and an effective length of up to 11.90λ, as well as PHs with three bends, can be obtained using this method. The formation mechanism of the PH is revealed by simulating the distribution of the field intensity with the finite element method and analyzing with ray optics. This is the first time that we introduce a function into the investigation of PH, paving a new way for a more interesting exploration of PH.

Photonic hook is a high-intensity, bent light focus with a proportional curvature to the wavelength of the incident light. Based on this unique light-bending phenomenon, a novel near-field photonic switch by means of a right-trapezoid dielectric Janus particle-lens embedded in the core of a planar waveguide is proposed for switching the photonic signals at two common optical communication wavelengths, 1310 nm and 1550 nm, by using numerical simulations. The signals at these two wavelengths can be guided to different routes according to their oppositely bent photonic hooks to realise wavelength selective switching. The switching mechanism is analysed by an in-house developed three-dimensional (3D) Poynting vector visualisation technology. It demonstrates that the 3D distribution and number of Poynting vector vortexes produced by the particle highly affect the shapes and bending directions of the photonic hooks causing the near-field switching, and multiple independent high-magnitude areas matched by the regional Poynting vector streamlines can form these photonic hooks. The corresponding mechanism can only be represented by 3D Poynting vector distributions and is being reported for the first time.

Structured light have made deep impacts on modern biotechnology and clinical practice, with numerous optical systems and lasers currently being used in medicine to treat disease. We demonstrate a new concept of fiber‐based optical hook scalpel. The subwavelength photonic hook is obtained in the vicinity of a shaped fiber tip with asymmetric radiation. A 1550 nm continuous‐wave source, commonly used for medical imaging, has been required. Photonic hook with a lateral feature size less than the half‐wavelength is achieved using a hemispherical shaped fiber tip with metallic mask. This breakthrough is carried out in ambient air by using a 4‐μm‐diameter fiber with a shaped tip. A good correlation is observed between the computed intensity distribution of photonic hook and the tip sizes. Photonic hook generated with a shaped fiber tip, easier to manipulate, shows far‐reaching benefits for potential applications such as ophthalmic laser surgery, super‐resolution microscopy, photolithography and material processing. [ABSTRACT FROM AUTHOR]

Spatial resolution of conventional optics, which is necessary for nondestructive trapping of microobjects, is limited by diffraction to a value equal to half of the radiation wavelength. Despite this limitation, use of optical methods is one of the main directions in biological and biomedical researches because only these methods have a minimal impact on living organisms. The rapid advance in this area is largely owing to the development of new optical technologies and the considerable advance in mesoscale photonics, which has allowed researchers to develop techniques for controlling structured beams for optical traps. In this work, we consider some recent trends in the field of optical manipulation based on mesoscale dielectric particles. [ABSTRACT FROM AUTHOR]

Recently, two special photonic jets, photonic hooks and twin photonic jets, have been proposed to deal with complex conditions in nanoscale manipulation. Photonic hooks are generated by a single light plane wave and an asymmetric microparticle, while the twin photonic jets are produced by two incident light beams. In this letter, we presented and demonstrated a method to combine photonic hooks and twin photonic jets. A single light plane wave and a symmetric microparticle, twin-ellipse microcylinder, are used in this research. The curvature degree, length and maximum E2 field enhancement of twin photonic hooks are varied significantly, with the change of refractive indices and shape of twin-ellipse microcylinder. And a liquid-immersed core-shell is built to achieve a flexible tunability. [ABSTRACT FROM AUTHOR]

Optical manipulation provides new insight into a wide range of physical phenomena and has engendered advanced applications in various fields. By utilizing near-field methods that overcome the diffraction limit, the ability to manipulate nanoparticles became feasible. In this paper, we analyze the displacement trajectories of a gold nanoparticle in the field of an ultrashort pulsed beam in symmetric (photonic nanojet) and symmetry-breaking (photonic hook) systems. We generate a symmetric optical force by illuminating a dielectric, micro-cylinder, and break the symmetry by adding a dielectric plate. We developed an efficient numerical method for calculating nanoparticle displacement under pulsed illumination which uses a stroboscopic map. Within this method, we revealed the influence of the plate position on the likeliness of different types of nanoparticle motion (i.e. stable, negative, or positive motion) in symmetric and symmetry-breaking configurations. Our work stimulates the development of experimental methods for optomechanical manipulation and opens a venue for future fundamental investigations for a range of practical applications, where accurate control over the mechanical motion of nanoscale objects is required. • Ultrashort pulses in symmetrical and symmetry-breaking systems induce nanoparticle displacement. • A Stroboscopic map was used for efficient calculation of the nanoparticle's trajectory. • Three cases of nanoparticle displacement were observed: attractive motion, repulsive motion and stable motion. • The degree of asymmetry can be controlled to achieve a higher probability of each type of motion. [ABSTRACT FROM AUTHOR]

The diffraction limit is a fundamental barrier in optical microscopy, which restricts the smallest resolvable feature size of a microscopic system. Microsphere-based microscopy has proven to be a promising tool for challenging the diffraction limit. Nevertheless, the microspheres have a low imaging contrast in air, which hinders the application of this technique. In this work, we demonstrate that this challenge can be effectively overcome by using partially Ag-plated microspheres. The deposited Ag film acts as an aperture stop that blocks a portion of the incident beam, forming a photonic hook and an oblique near-field illumination. Such a photonic hook significantly enhanced the imaging contrast of the system, as experimentally verified by imaging the Blu-ray disc surface and colloidal particle arrays.

The photonic hook (PH) is a new type of curved light beam, which has promising applications in various fields such as nanoparticle manipulation, super-resolution imaging, and so forth. Herein, we proposed a new approach of utilizing patchy microcylinders for the generation of PHs. Numerical simulation based on the finite-difference time-domain method was used to investigate the field distribution characteristics of the PHs. By rotating the patchy microcylinder, PHs with different curvatures can be effectively generated, and the PH with a bending angle of 28.4∘ and a full-width-half-maximum of 0.36 λ can be obtained from 1 μm-diameter patchy microcylinders.

The study of accelerating Airy-family beams has made significant progress, not only in terms of numerical and experimental investigations, but also in conjunction with many potential applications. However, the curvature of such beams (and hence their acceleration) is usually greater than the wavelength. Relatively recently, a new type of localized wave beams with subwavelength curvature, called photonic hooks, was discovered. This paper briefly reviews the substantial literature concerning photonic jet and photonic hook phenomena, based on the photonic jet principle. Meanwhile, the photonic jet ensemble can be produced by optical wave diffraction at 2D phase diffraction gratings. The guidelines of jets’ efficient manipulation, through the variation of both the shape and spatial period of diffraction grating rulings, are considered. Amazingly, the mesoscale dielectric Janus particle, with broken shape or refractive index symmetry, is used to generate the curved photonic jet—a photonic hook—emerging from its shadow-side surface. Using the photonic hook, the resolution of optical scanning systems can be improved to develop optomechanical tweezers for moving nanoparticles, cells, bacteria and viruses along curved paths and around transparent obstacles. These unique properties of photonic jets and hooks combine to afford important applications for low-loss waveguiding, subdiffraction-resolution nanopatterning and nanolithography.

The diffraction limit is a fundamental barrier in optical microscopy, which restricts the smallest resolvable feature size of a microscopic system. Microsphere-based microscopy has proven to be a promising tool for challenging the diffraction limit. Nevertheless, the microspheres have a low imaging contrast in air, which hinders the application of this technique. In this work, we demonstrate that this challenge can be effectively overcome by using partially Ag-plated microspheres. The deposited Ag film acts as an aperture stop that blocks a portion of the incident beam, forming a photonic hook and an oblique near-field illumination. Such a photonic hook significantly enhanced the imaging contrast of the system, as experimentally verified by imaging the Blu-ray disc surface and colloidal particle arrays. [ABSTRACT FROM AUTHOR]

The photonic hook (PH) is a new type of curved light beam, which has promising applications in various fields such as nanoparticle manipulation, super-resolution imaging, and so forth. Herein, we proposed a new approach of utilizing patchy microcylinders for the generation of PHs. Numerical simulation based on the finite-difference time-domain method was used to investigate the field distribution characteristics of the PHs. By rotating the patchy microcylinder, PHs with different curvatures can be effectively generated, and the PH with a bending angle of 28.4 ∘ and a full-width-half-maximum of 0.36 λ can be obtained from 1 μ m-diameter patchy microcylinders. [ABSTRACT FROM AUTHOR]

• A curved hollow photonic jet is formed from a spherical particle illuminated by a Bessel-Gaussian beam. • The field of Bessel-Gaussian beam is expressed in terms of angular spectrum decomposition method. • Near-field of scattered light is numerically calculated with the generalized Mie theory. Researches have shown that an electromagnetic field can be made to curve after propagation through a small asymmetric particle in recent years. This effect was called photonic hook or curved photonic jet. It was believed that a symmetric particle like spheres and cylinders produces straight photonic jet only. In this work, we report a curved hollow photonic jet produced by a spherical particle under the illumination of a circular high-order Bessel-Gaussian beam. With the numerical simulation, it is found that the structure of the curved hollow photonic jet depends closely on the parameters of both the beam and particle. The work may open a pathway to generate new types of curved photonic jets from symmetric particle illuminated by shaped beams. [ABSTRACT FROM AUTHOR]

The mechanism of formation of a terahertz jet by a dielectric cuboid and a sphere surrounded by ideally conducting screens is considered. The maximum screen influence is observed when the screen is located near the alight cuboid base. The screen influence eases when the screen is shifting along the dielectric object. Power flux density localization area is almost completely shifted inside the object when the screen is situated in the center. The minimum influence is observed when screen placed in the shadow plane of the cuboid base. This effect caused by the screen influence on electric field component tangential to the side edges and thus on the power flux directed to the central axis of the object. The screen influence on the terahertz jet in spherical object has been compared. Value of the power flux density after passing the object is higher in a cuboid, but the focusing characteristics are better (appearing on shorter distances) in a sphere. [ABSTRACT FROM AUTHOR]

The study of accelerating Airy-family beams has made significant progress, not only in terms of numerical and experimental investigations, but also in conjunction with many potential applications. However, the curvature of such beams (and hence their acceleration) is usually greater than the wavelength. Relatively recently, a new type of localized wave beams with subwavelength curvature, called photonic hooks, was discovered. This paper briefly reviews the substantial literature concerning photonic jet and photonic hook phenomena, based on the photonic jet principle. Meanwhile, the photonic jet ensemble can be produced by optical wave diffraction at 2D phase diffraction gratings. The guidelines of jets' efficient manipulation, through the variation of both the shape and spatial period of diffraction grating rulings, are considered. Amazingly, the mesoscale dielectric Janus particle, with broken shape or refractive index symmetry, is used to generate the curved photonic jet—a photonic hook—emerging from its shadow-side surface. Using the photonic hook, the resolution of optical scanning systems can be improved to develop optomechanical tweezers for moving nanoparticles, cells, bacteria and viruses along curved paths and around transparent obstacles. These unique properties of photonic jets and hooks combine to afford important applications for low-loss waveguiding, subdiffraction-resolution nanopatterning and nanolithography. [ABSTRACT FROM AUTHOR]

Optical hook, a kind of curved high‐intensity light beam, has aroused tremendous interests during the past several years, and its experimental observation has been reported in the terahertz band. The existing approaches to generate such beams depend on the effect of "curved photonic nanojet" stemming from transparent and symmetry breaking high‐index dielectric slab, and thus are restricted by the limited material selection, large device footprint, and fixed trajectory. Herein, the generation of photonic hooks in the visible band based on ultra‐thin metalenses is reported. The strategy can overcome the limitations mentioned above and the photonic hook can be easily tuned by changing the incidence angle or wavelength. Such flexibility is likely to widen the future applications of such unique beam in particle trapping, optical tweezers, and superresolution imaging. [ABSTRACT FROM AUTHOR]

Today the surface plasmon‐polariton (SPP) waves propagating along the curve trajectory are the only plasmonic beams of the Airy family. Herein, a new class of curved surface plasmon wave, the photonic hook plasmon (PHP), is introduced. The PHP is created using the in‐plane focusing of the SPP wave through an asymmetric dielectric particle. This is fundamentally simpler than the generation of the SPP Airy‐family beams. The PHP propagates along a wavelength‐scaled curved trajectory with radius less than the SPP wavelength, which represents the smallest radius of curvature ever recorded for an SPP beam, and can exist despite the strong energy dissipation at metal surface. Today the surface plasmon‐polariton (SPP) waves propagating along the curve trajectory are the only plasmonic beams of the Airy family. A new class of curved surface plasmon wave, the photonic hook plasmon (PHP), is introduced. The PHP propagates along wavelength‐scaled curved trajectory with radius less than the SPP wavelength, which represents the smallest radius of curvature ever recorded for the SPP beam. [ABSTRACT FROM AUTHOR]