Photonic Hook Research Articles

Curved beam generation and its experimental realization by rectangular prism with asymmetric polynomial back surface

With the discovery of self-accelerating beams, possibility of obtaining curved light beams in free space has been realized. These special beams paved the way for many new applications as well as the exploration of novel beam types. Recently, great research effort has been conducted to realize different types of curved beams such as photonic hook and airy beam. These curved types of beams are obtained by introducing structural asymmetry or applying non-uniform dielectric distribution to the input and output face of the structure. With this regard, we propose specially designed asymmetric structure with polynomial back surface which generates curved light beams. Proposed lossless dielectric structure can generate curved beams at frequencies varying from 15.78 GHz to 20.09 GHz and corresponding curvature angles of minimum 41.34° and maximum 57.58°, respectively. The physical background of the curved beam formation is based on interference of the exiting light waves that diffract on upper and bottom polynomial surfaces which provides phase modulation leading to the curved trajectory of the propagating light. In addition, the observed beam steering effect is further investigated and the experimental verification in microwave region is conducted to verify our design’s operation principle.

Photonic Hook with Modulated Bending Angle Formed by Using Triangular Mesoscale Janus Prisms

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.

Generation of multiple photonic hooks in reflection mode

Generation of multiple photonic hooks (PHs) at THz region in reflection mode by a multi-dielectric structure that consists of periodical or aperiodical scatterer units on top surface of a reflection screen has been systematically studied. The study focuses on effects of geometric and optical parameters of the multi-dielectric structure on characteristics of the PHs generated, especially the bending angle. These geometric and optical parameters include spacing between adjacent scatterer units, length of reflection screen, as well as the size, refractive index and number of scatterer units. The results show that these geometric and optical parameters are key factors in tailoring the performance of the multiple PHs generated. The spacing determines bending direction of PHs and there exists a critical spacing value. Smaller than this critical value, the PHs generated bend outwards. Larger than this critical value, the PHs bend inwards. In addition, the spacing can be also used to effectively adjust the intensity and bending angle of the PHs. Screen length affects mainly PH's bending. The size and refractive index differences between scatterer units introduce additional optical inhomogeneity that leads to the generation of asymmetrical multiple PHs. Finally, the possibility of generation of an arrayed PHs in the reflection mode is demonstrated.

Experimental Proof-of-Concept of a Spatial Photonic Switch Based on an Off-Axis Zone Plate in Millimeter Wavelength Range

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.

Generation of Photonic Hooks under Point-Source Illumination from Patchy Microcylinders

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.

Array of photonic hooks generated by multi-dielectric structure

Generation of array of photonic hooks (PHs) by a multi–dielectric structure that consists of periodically arrayed scatterer units has been systematically studied. The study focuses on the effects of geometric and optical parameters of the multi–dielectric structure on the characteristics of generated PHs, especially their bending angles. These geometric and optical parameters include size, shape, refractive index and number of scatterer units, and their adjacent spacing. The results show that the spacing, size and refractive index play a predominant role in tailoring the performance of the PHs array, and the spacing affects mainly the characteristics of a pair of symmetrical PHs while the size and refractive index differences between scatterer units affect mainly those of asymmetrical PHs as a result of the introduction of optical inhomogeneity. In the aspect of scatterer shape, for a multi–dielectric structure that consists of some cylinders, as the light wave is incident parallel (perpendicular) to the cylinder axis, its scattering characteristics are similar to those of the multi–dielectric structure that consists of some cuboids (spheres). In particular, for a structure consisted of cylinders or cuboids with long length in the z direction, an intensive photonic nanojet is additionally generated and located between the paired PHs provided that the wave is incident perpendicular to the cylinder axis or the longest side of cuboid. In the aspect of scatterer unit number, the multi–dielectric structures of odd and even scatterer units generate PHs with different characteristics. The paired PHs generated by multi–dielectric structure with equal spacings always bend outward. However, the paired PHs may bend inward provided that the multi–dielectric structure is designed properly. We have also studied the features of 2D PHs array. The results show that the 2D PHs array displays similar features to the 1D case. The application potential of both 1D and 2D PHs arrays is evaluated.

Photonic Hooks Generated by a Concave Micro-Cylinder Based on Structure-Constrained Functions.

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.

Near-Field Light-Bending Photonic Switch: Physics of Switching Based on Three-Dimensional Poynting Vector Analysis

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.

Terahertz microscope with oblique subwavelength illumination: design principle

It is shown that the image contrast in the air when using a microscope based on dielectric microparticles with a size of the order of wavelength can be significantly enhanced with the help microparticles that provide the formation of the radiation localisation region at an angle to the direction of radiation incidence (at an angle to the optical axis). For this purpose, a screen is placed in front of the particle, which blocks part of the incident beam, forming a photonic hook or a photonic jet (terajet) with oblique illumination in the near field.

The concept of a miniature all-optical space switch based on the photonic hook effect

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.

Super-Resolution Imaging with Patchy Microspheres

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.

Towards structured SPP manipulation of light at the nanoscale

Surface plasmon photonics is a rapidly developing area of physics, optics, and nanotechnology. The unique ability of meso- and nano-structures to manipulate light in the subwavelength range down to nanoscale volumes stimulated their use in a vast research endeavours. The investigations are driven by interests in both fundamental and practical applications aspects where plasmonic light concentrators elegantly interface mesoscale dielectric structure with thin metal films. The effects of a photonic nanojet and a photonic hook, discovered by Minins, have been studied in sufficient detail in the literature, but only recently have they been able to be confirmed experimentally for low-dimensional systems – in-plane surface plasmon waves. The nature of these phenomenas lies in the dispersion of the phase velocity of waves inside the dielectric structure, which leads to constructive interference of the transmitted, diffracted, and near-field waves. Our results set the grounds for in-plane plasmonic wavelength scaled optics with unprecedented control of the energy flow at the nanoscale, and shown a way toward realizing the densely packed optical elements needed for future plasmonic and optical devices.

Generation of Photonic Hooks from Patchy Microcylinders

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.

Diffraction limited photonic hook via scattering and diffraction of dual-dielectric structures

Photonic hooks have demonstrated to be great candidates for multiple applications ranging from sensing up to optical trapping. In this work, we propose a mechanism to produce such bent structured light beams by exploiting the diffraction and scattering generated by a pair of dielectric rectangles immersed in free space. It is shown how the photonic hooks are generated away from the output surface of the dielectrics by correctly engineering each individual dielectric structure to generate minimum diffraction and maximum scattering along the propagation axis. Different scenarios are studied such as dual-dielectric structures having different lateral dimensions and refractive index as well as cases when both dielectrics have the same lateral dimensions. The results are evaluated both numerically and theoretically demonstrating an excellent agreement between them. These results may open new avenues for optical trapping, focusing and sensing devices via compact and simple dual-dielectric structures.

Photonic hook generated by the Janus microcylinder under point-source illumination

A photonic hook (PH) is a high-intensity, curved focusing beam with a subwavelength waist based on the photonic nanojet effect. It is generally created by illuminating mesoscale transparent particles using optical plane waves. In this work, we numerically explore the generation of the PH supported by the Janus microcylinder under point-source illumination. To simulate the photonic intensity distributions near the shadow surface of the Janus microcylinder, a finite-difference time-domain technique is used. The power flow distributions near the Janus microcylinder are examined for working in the visible spectrum. Due to the asymmetric vortices of Poynting vectors, the PH with a large bending angle can be produced. By changing the location of the point-source illumination, the shape and curvature of the PH can be adjusted efficiently. Moreover, when the point-source illumination is located close to the Janus microcylinder, a long focal length PH can be present. Based on the numerical results, we propose a practical modeling scheme for optical imaging using a microscope where the light source is close to the target.

Multispectral Photonic Jet Shaping and Steering by Control of Tangential Electric Field Component on Cuboid Particle

In this study, we present the simulations and experimental observations of photonic jet (PJ) shaping by control of tangential electric field components at illuminating wavelengths of 405 nm, 532 nm, and 671 nm. The PJs are generated by a single dielectric 4-micrometer cube that was fabricated from polydimethylsiloxane (PDMS). The dielectric cube is deposited on a silicon substrate and placed on two aluminum masks with a width equal to the side length of the cube. Due to the appearance of the metal masks, the focal length and decay length of the generated PJs decreased almost twice, while the PJ resolution increased 1.2 times. Thus, PJ shaping can be controlled by the presence of the metal mask along the lateral surface of the cube without changing the external shape or internal structure of the cube. This effect is based on the control of the tangential components of the electric field along the lateral surface of the cube. In the case of a one-sided metal mask, the effect of optical deflection and bending is predicted to form a photonic hook. Due to the low cost of these dielectric cubes, they have potential in far-field systems to better meet the requirements of modern optical integration circuits and switches.

Concept of a miniature photonic spatial switch based on an off-axis zone plate

A new concept of an all-optical wavelength-selective two-channel switch based on the photonic hook effect without the use of micromechanical devices or nonlinear materials is proposed. A prototype of such a device based on an off-axis Fresnel zone plate is considered and its main parameters are discussed. Due to the unique property of the photonic hook to change its curvature with respect to the irradiation wavelength λ, this switch is a promising candidate for the implementation of optical switching in modern optoelectronics and miniature ‘on-a-chip’ devices. Numerical simulation shows that the optical isolation of switched channels for a switch with linear dimensions of about (6λ)3 based on an off-axis zone plate can reach 18 – 20 dB during operation in the wavelength range of 1.5 – 1.9 μm.

Wavelength‐Scale Photonic Space Switch Proof‐Of‐Concept Based on Photonic Hook Effect

AbstractThe proof‐of‐concept of a new wavelength‐scaled all‐optical two‐channel switch based on the photonic hook phenomenon is proposed and demonstrated. By means of the numerical finite‐difference time‐domain simulations, several prototypes of such devices are considered based on dielectric microstructures with broken symmetry of both geometric shape and optical properties without the use of micromechanical devices or non‐linear materials. Due to the unique property of the photonic hook to change its curvature depending on the optical wavelength, the proposed switch is a promising candidate for the implementation of optical switching in modern optoelectronics and miniature “on‐chip” devices. Optical isolation that is close to 20 dB is discovered at the wavelengths of 1.5 and 1.9 µm for a dielectric Janus microbar‐based switch with linear dimensions of about (6λ)3 (λ is the wavelength of the incident plane wave).

Inflection point: a perspective on photonic nanojets

When light propagates through the edge or middle part of a microparticle’s incoming interface, there is a basic rule that light converges and diverges rapidly or slowly at the output port. These two parts are referred to as the region of rapid change (RRC) and region of slow change (RSC), respectively. Finding the boundary point between RRC and RSC is the key to reveal and expound upon this rule scientifically. Based on the correlation between light convergence–divergence and the slope of emergent light, combined with the relationship between a natural logarithm and growth in physical reality and the second derivative of a function in practical significance, we determine the boundary point between RRC and RSC, namely, the inflection point. From such a perspective, a photonic nanojet (PNJ) and near-field focusing by light irradiation on RSC and RRC, as well as the position of the inflection point under different refractive index contrasts and the field distribution of light focusing, are studied with finite-element-method-based numerical simulation and ray-optics-based theoretical analysis. By illuminating light of different field intensity ratios to the regions divided by the inflection point, we demonstrate the generation of a photonic hook (PH) and the modulation of PNJ/PH in a new manner.

Curved photonic jet produced from a spherical particle illuminated by a Bessel-Gaussian beam

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.