Showing papers on "Transformation optics published in 2018"
TL;DR: In this article, a fully metallic Luneburg lens was proposed to produce a link between 3-D homogeneous surfaces and 2-D dielectric lenses where the propagation is only in the air.
Abstract: Non-Euclidean transformations have been recently proposed to produce a link between 3-D homogeneous surfaces and 2-D dielectric lenses. Therefore, the propagation in a geometrical surface has the same response of an equivalent refractive index distribution. By using this concept, we propose here a fully metallic Luneburg lens where the propagation is only in the air. Two metallic plates, following a curved shape, are employed to support the propagation mimicking the designed curvature. To reduce the height of the required curvature, the surface has been mirrored twice with respect to two $z$ constant planes. The lens is fed by 11 waveguide ports spaced with an angle of 12.5° providing 1-D beam scanning over an angular range of ±62.5°. A prototype is manufactured and measured with a good agreement with the simulated results between 25 and 36 GHz to demonstrate the concept.
128 citations
TL;DR: In this article, a flat compact dual-polarized Luneburg lens antenna is proposed and implemented using the printed-circuit-board-stacked gradient-index metamaterials for beam scanning and multibeam applications at X-bands.
Abstract: Based on a transformation optics method, a flat compact dual-polarized Luneburg lens antenna is proposed and implemented using the printed-circuit-board-stacked gradient-index metamaterials for beamscanning and multibeam applications at X-bands. The transformed material properties of the planar Luneburg lens are designed with 17-layered permittivity distribution of polynomials. Each layer is discretized into $41 \times 41$ pixels made of broadband and less polarization-dependent unit cells responsible for desired index distributions. The effects of transformation, approximation, and discretization on the lens performance are analyzed comprehensively. Also, to validate the implementation method, a flat Luneburg lens with a thickness of 14.1 mm, a focal length of 28 mm, and an aperture size of $98.9 \times 98.9$ mm2 is designed and tested. A stacked aperture-coupled patch antenna operating at 10 GHz is applied as a feeder. The measured results show that the proposed antenna can operate over a bandwidth of ~20% with an antenna efficiency of 32%, a cross-polarization level of <−17.1 dB, as well as the maximum gain of 15.9/16.35 dBi and a scanning angle of ±32°/±35° for two orthogonal polarizations, respectively. The presented flat Luneburg lens antenna featuring broad bandwidth, high gain, wide scanning angle, and easy fabrication has a high potential in 5G wireless communication, imaging, and remote sensing applications.
115 citations
TL;DR: A synthetic paradigm with strictly full parameters and omnidirectionality is reported simultaneously to address this long-held issue for molding heat flow and experimentally demonstrate a series of noncentrosymmetric thermal metadevices that may open a new avenue to manipulating the Laplacian and wave-dynamic fields in ways previously inconceivable.
Abstract: Since the advent of transformation optics and scattering cancelling technology, a plethora of unprecedented metamaterials, especially invisibility cloaks, have been successfully demonstrated in various communities, e.g., optics, acoustics, elastic mechanics, dc electric field, dc magnetic field, and thermotics. A long-held captivation is that transformation-optic metamaterials of anisotropic or noncentrosymmetric geometry (e.g., ellipsoids) commonly come along with parameter approximation/simplification or directional functions. Here, a synthetic paradigm with strictly full parameters and omnidirectionality is reported simultaneously to address this long-held issue for molding heat flow and experimentally demonstrate a series of noncentrosymmetric thermal metadevices. It changes the usual perception that transformation thermotic/dc/acoustic metamaterials are just a direct and simplified derivatives of the transformation-optic counterpart. Instead, the proposed methodology solves an intriguingly important and challenging problem that is not possibly achievable for transformation-optic metamaterials. The approach is rigorous, exact, robust, and yet elegantly facile, which may open a new avenue to manipulating the Laplacian and wave-dynamic fields in ways previously inconceivable.
78 citations
TL;DR: A wide-angle scanning conformal phased array based on all-dielectric QCTO lens is designed and experimentally demonstrated, paving the way to a robust but efficient array synthesis, as well as multi-beam and beam forming realization of conformal arrays via transformation optics.
Abstract: Transformation Optics has been proven a versatile technique for designing novel electromagnetic devices and it has much wider applicability in many subject areas related to general wave equations. Among them, quasi-conformal transformation optics (QCTO) can be applied to minimize anisotropy of transformed media and has opened up the possibility to the design of broadband antennas with arbitrary geometries. In this work, a wide-angle scanning conformal phased array based on all-dielectric QCTO lens is designed and experimentally demonstrated. Excited by the same current distribution as such in a conventional planar array, the conformal system in presence of QCTO lens can preserve the same radiation characteristics of a planar array with wide-angle beam-scanning and low side lobe level (SLL). Laplace’s equation subject to Dirichlet-Neumann boundary conditions is adopted to construct the mapping between the virtual and physical spaces. The isotropic lens with graded refractive index is realized by all-dielectric holey structure after an effective parameter approximation. The measurements of the fabricated system agree well with the simulated results, which demonstrate its excellent wide-angle beam scanning performance. Such demonstration paves the way to a robust but efficient array synthesis, as well as multi-beam and beam forming realization of conformal arrays via transformation optics.
73 citations
Imperial College London1, University of Sannio2, Nanjing University3, University of Exeter4, University of Birmingham5, Royal Institute of Technology6, Chalmers University of Technology7, Vrije Universiteit Brussel8, University of Siena9, Queen Mary University of London10, Lancaster University11, Cockcroft Institute12, Oak Ridge National Laboratory13, Purdue University14, Weizmann Institute of Science15, University of Maryland, College Park16, Towson University17, Karlsruhe Institute of Technology18, Duke University19
TL;DR: The contributors to this Roadmap, who are all renowned practitioners or inventors of transformation optics, will give their perspectives into the field's status and future development.
Abstract: Transformation optics asks, using Maxwell's equations, what kind of electromagnetic medium recreates some smooth deformation of space? The guiding principle is Einstein's principle of covariance: that any physical theory must take the same form in any coordinate system. This requirement fixes very precisely the required electromagnetic medium. The impact of this insight cannot be overestimated. Many practitioners were used to thinking that only a few analytic solutions to Maxwell's equations existed, such as the monochromatic plane wave in a homogeneous, isotropic medium. At a stroke, transformation optics increases that landscape from 'few' to 'infinity', and to each of the infinitude of analytic solutions dreamt up by the researcher, there corresponds an electromagnetic medium capable of reproducing that solution precisely. The most striking example is the electromagnetic cloak, thought to be an unreachable dream of science fiction writers, but realised in the laboratory a few months after the papers proposing the possibility were published. But the practical challenges are considerable, requiring meta-media that are at once electrically and magnetically inhomogeneous and anisotropic. How far have we come since the first demonstrations over a decade ago? And what does the future hold? If the wizardry of perfect macroscopic optical invisibility still eludes us in practice, then what compromises still enable us to create interesting, useful, devices? While three-dimensional (3D) cloaking remains a significant technical challenge, much progress has been made in two dimensions. Carpet cloaking, wherein an object is hidden under a surface that appears optically flat, relaxes the constraints of extreme electromagnetic parameters. Surface wave cloaking guides sub-wavelength surface waves, making uneven surfaces appear flat. Two dimensions is also the setting in which conformal and complex coordinate transformations are realisable, and the possibilities in this restricted domain do not appear to have been exhausted yet. Beyond cloaking, the enhanced electromagnetic landscape provided by transformation optics has shown how fully analytic solutions can be found to a number of physical scenarios such as plasmonic systems used in electron energy loss spectroscopy and cathodoluminescence. Are there further fields to be enriched? A new twist to transformation optics was the extension to the spacetime domain. By applying transformations to spacetime, rather than just space, it was shown that events rather than objects could be hidden from view; transformation optics had provided a means of effectively redacting events from history. The hype quickly settled into serious nonlinear optical experiments that demonstrated the soundness of the idea, and it is now possible to consider the practical implications, particularly in optical signal processing, of having an 'interrupt-without-interrupt' facility that the so-called temporal cloak provides. Inevitable issues of dispersion in actual systems have only begun to be addressed. Now that time is included in the programme of transformation optics, it is natural to ask what role ideas from general relativity can play in shaping the future of transformation optics. Indeed, one of the earliest papers on transformation optics was provocatively titled 'General Relativity in Electrical Engineering'. The answer that curvature does not enter directly into transformation optics merely encourages us to speculate on the role of transformation optics in defining laboratory analogues. Quite why Maxwell's theory defines a 'perfect' transformation theory, while other areas of physics such as acoustics are not apparently quite so amenable, is a deep question whose precise, mathematical answer will help inform us of the extent to which similar ideas can be extended to other fields. The contributors to this Roadmap, who are all renowned practitioners or inventors of transformation optics, will give their perspectives into the field's status and future development.
72 citations
TL;DR: In this article, a metasurface composed of a subwavelength metallic slit array embedded in an asymmetric dielectric environment can exhibit either extraordinary optical transmission (EOT) or extraordinary optical diffraction (EOD).
Abstract: We show that a metasurface composed of a subwavelength metallic slit array embedded in an asymmetric dielectric environment can exhibit either extraordinary optical transmission (EOT) or extraordinary optical diffraction (EOD). The cascaded refractive indices of the dielectrics can leverage multiple decaying passages into variant subsections with different diffraction order combinations according to the diffraction order chart in the k-vector space, providing a flexible mean to tailor resonance decaying pathways of the metallic slit cavity mode by changing the wavevector of the incident light. As a result, either the zeroth transmission or −1st reflection efficiencies can be enhanced to near unity by the excitation of the localized slit cavity mode, leading to either EOT or EOD in a single structure, depending on the illumination angle. Based on this appealing feature, a multifunctional metasurface that can switch its functionality between transmission filter, mirror, and off-axis lens is demonstrated. Our findings provide a convenient way to construct multifunctional miniaturized optical components on a single planar device.
63 citations
TL;DR: An accurate theoretical model is proposed for designing tilted SWG structures based on rotated uniaxial crystals that is functional over a wide wavelength range and for both the fundamental and higher order modes.
Abstract: Subwavelength grating (SWG) structures are an essential tool in silicon photonics, enabling the synthesis of metamaterials with a controllable refractive index Here we propose, for the first time to the best of our knowledge, tilting the grating elements to gain control over the anisotropy of the metamaterial Rigorous finite difference time domain simulations demonstrate that a 45° tilt results in an effective index variation on the fundamental TE mode of 023 refractive index units, whereas the change in the TM mode is 20 times smaller Our simulation predictions are corroborated by experimental results We furthermore propose an accurate theoretical model for designing tilted SWG structures based on rotated uniaxial crystals that is functional over a wide wavelength range and for both the fundamental and higher order modes The proposed control over anisotropy opens promising venues in polarization management devices and transformation optics in silicon photonics
60 citations
TL;DR: By considering flexural waves on a curved plate with geometric curvature, the stringent material requirement can be relaxed, and a two-dimensional analog of a wormhole is demonstrated using homogeneous materials within a curved laboratory frame.
Abstract: Transformation optics (TO) can be used to investigate nontrivial spacetime structures with inhomogeneous materials. However, the extreme curvature and large refractive indices make the implementation of a wormhole challenging. By considering flexural waves on a curved plate with geometric curvature, the stringent material requirement can be relaxed, and we demonstrate a two-dimensional analog of a wormhole using homogeneous materials within a curved laboratory frame. TO is used to understand wave propagation in such a curved space. This curved elastic space approach allows us to investigate not only geodesics but also wave redirection, tunneling, and virtual caustics of the wormhole, and will be useful to develop curvature-driven wave front shaping in general.
57 citations
TL;DR: This work design and experimentally demonstrate two annular devices for concentrating waves, which employ gradient depth profiles based on Fabry-Pérot resonances, and shows that transformation optics is an effective framework for designing devices to improve the efficiency of wave energy collection.
Abstract: By introducing concepts from transformation optics to the manipulation of water waves, we design and experimentally demonstrate two annular devices for concentrating waves, which employ gradient depth profiles based on Fabry-Perot resonances. Our measurements and numerical simulations confirm the concentrating effect of the annular devices and show that they are effectively invisible to the water waves. We show that transformation optics is thus an effective framework for designing devices to improve the efficiency of wave energy collection, and we expect potential applications in coastline ocean engineering.
44 citations
TL;DR: The present metasurface cloak can work at dual frequencies based on multi-resonance principle and will be very useful in future broadband macroscopic cloaks design with low profiles, light weights, and easy access.
Abstract: Metasurfaces provide an alternative way to design three-dimensional arbitrary-shaped carpet cloaks with ultrathin thicknesses. Nevertheless, the previous metasurface carpet cloaks work only at a single frequency. To overcome this challenge, we here propose a macroscopic metasurface carpet cloak. The cloak is designed with a metasurface of a few layers that exhibit a special spatial distribution of the conductance and inductance in the unit cell; therefore, it can fully control the reflection phases at several independent frequencies simultaneously. Because of this, the present metasurface cloak can work at dual frequencies based on multi-resonance principle. The proposed design methodology will be very useful in future broadband macroscopic cloaks design with low profiles, light weights, and easy access.
43 citations
TL;DR: In this paper, the dispersion bias associated with space-time varying modulations of inertial and stiffness parameters of the base material and the resonant components is derived, and the resultant dispersion biases onsets intriguing features culminating in a break-up of both acoustic and optic propagation modes and one-way local resonance band gaps.
TL;DR: This work proposes an innovative OAM generation method based on transformation optics (TO), which provides an effective way to realize a conversion from plane waves to vortex waves, which can greatly facilitate the potential implementation of OAM waves in microwave wireless communication systems.
Abstract: Orbital angular momentum (OAM) vortex waves generated by conventional spiral phase plates and metasurfaces have been widely discussed. In this work, we propose an innovative OAM generation method based on transformation optics (TO). By solving Laplace’s equation with specific boundary conditions, an oblate cylindrical shaped physical domain is designed to imitate a gradient shaped virtual domain which is able to generate a vortex beam upon reflection. As a proof-of-concept demonstration, a broadband all-dielectric microwave lens for vortex beam generation is presented with a topological charge of + 1. The corresponding far-field patterns as well as near-field helical phase and doughnut-shaped amplitude distributions of the lens, obtained from numerical simulations, are reported along with a wide operational bandwidth spanning from 8 to 16 GHz. As a transformation method, the proposed TO technique provides an effective way to realize a conversion from plane waves to vortex waves, which can greatly facilitate the potential implementation of OAM waves in microwave wireless communication systems.
TL;DR: The singular metasurface as mentioned in this paper is a subwavelength surface formed by nanostructuring a metal surface at the sub-wavelength scale and is used for the control of radiation in varied ways.
Abstract: Metasurfaces can be formed by nanostructuring a metal surface at the subwavelength scale and are used for the control of radiation in varied ways. Extremely sharp points on the surface give rise to singular metasurfaces, which efficiently convert incident radiation into surface plasmons. These plasmons slowly approach the singular points, which act as energy sinks, thus leading to increased absorption for a wide frequency band. This continuous spectrum is the main characteristic of singular metasurfaces: while being periodic they are actually equivalent to a bulk structure in one extra dimension and for that reason they present a continuous rather than discrete set of modes.
TL;DR: In this article, a general covariant, coordinate-free framework for electrodynamics in general dielectric media residing in curved background space-times is developed. But the framework is restricted to the case of birefringent media.
Abstract: While the postulate of covariance of Maxwell's equations for all inertial observers led Einstein to special relativity, it was the further demand of general covariance---form invariance under general coordinate transformations, including between accelerating frames---that led to general relativity. Several lines of inquiry over the past two decades, notably the development of metamaterial-based transformation optics, has spurred a greater interest in the role of geometry and space-time covariance for electrodynamics in ponderable media. I develop a generally covariant, coordinate-free framework for electrodynamics in general dielectric media residing in curved background space-times. In particular, I derive a relation for the spatial medium parameters measured by an arbitrary timelike observer. In terms of those medium parameters I derive an explicit expression for the pseudo-Finslerian optical metric of birefringent media and show how it reduces to a pseudo-Riemannian optical metric for nonbirefringent media. This formulation provides a basis for a unified approach to ray and congruence tracing through media in curved space-times that may smoothly vary among positively refracting, negatively refracting, and vacuum.
TL;DR: 3D homogeneous polyhedral transformation and a spatially invariant refractive index discretization that considerably reduce the coupling of the electromagnetic components of visible light allow for a major simplification in the design of 3D invisibility cloaks, which can now be created at a large scale using homogeneous and isotropic materials.
Abstract: The concept of an invisibility cloak is a fixture of science fiction, fantasy, and the collective imagination. However, a real device that can hide an object from sight in visible light from absolutely any viewpoint would be extremely challenging to build. The main obstacle to creating such a cloak is the coupling of the electromagnetic components of light, which would necessitate the use of complex materials with specific permittivity and permeability tensors. Previous cloaking solutions have involved circumventing this obstacle by functioning either in static (or quasistatic) fields where these electromagnetic components are uncoupled or in diffusive light scattering media where complex materials are not required. In this paper, concealing a large-scale spherical object from human sight from three orthogonal directions is reported. This result is achieved by developing a 3D homogeneous polyhedral transformation and a spatially invariant refractive index discretization that considerably reduce the coupling of the electromagnetic components of visible light. This approach allows for a major simplification in the design of 3D invisibility cloaks, which can now be created at a large scale using homogeneous and isotropic materials.
TL;DR: A three-dimensional finite-difference time-domain method is combined with the genetic optimization approach to generate the cloaking structure to directionally cloak a cylindrical object made of a perfect electrical conductor by suppressing the undesired scattered fields around the object.
Abstract: In this Letter, the design of a directional optical cloaking by a genetic algorithm is proposed and realized experimentally. A three-dimensional finite-difference time-domain method is combined with the genetic optimization approach to generate the cloaking structure to directionally cloak a cylindrical object made of a perfect electrical conductor by suppressing the undesired scattered fields around the object. The optimization algorithm designs the permittivity distribution of the dielectric polylactide material to achieve an optical cloaking effect. Experimental verifications of the designed cloaking structure are performed at microwave frequencies, where the proposed structure is fabricated by 3D printing. The imperfect conformal mapping from a large-scale permittivity distribution and the compensation of the remaining scattering by a small-scale permittivity distribution are the basic physical mechanisms of the proposed optical cloaking.
TL;DR: In this article, the authors exploit the extra degrees of freedom of a core-shell dielectric sphere to obtain a particle whose duality symmetry is more than one order of magnitude better than previously reported non-magnetic objects.
Abstract: Material electromagnetic duality symmetry requires a system to have equal electric and magnetic responses. Electromagnetic duality enables technologically important effects like artificial optical activity and zero back-scattering, is a requirement for metamaterials in transformation optics, Huygens wave-front control, and maximal electromagnetic chirality, and appears in topological photonic systems. Intrinsically dual materials that meet the duality conditions at the level of the constitutive relations do not exist in many frequency bands. Nevertheless, discrete objects like metallic helices and homogeneous dielectric spheres can be engineered to approximate the dual behavior. The discrete objects can then be used as building blocks with the objective of obtaining composite systems with high duality symmetry. Here, we exploit the extra degrees of freedom of a core-shell dielectric sphere to obtain a particle whose duality symmetry is more than one order of magnitude better than previously reported non-magnetic objects. We show that the improvement is transferred onto the duality symmetry of composite objects when the core-shell particle is used as a building block instead of homogeneous spheres.
TL;DR: In this paper, the authors proposed a cloaking technique based on a homogeneous plasmonic layer of negative permittivity and a multilayer structure that cancels the scattering of the cloaked object.
Abstract: In recent years, there has been a growing interest in developing invisibility cloaks that can conceal an object. These techniques are often based either on coating a dielectric or conducting object with a homogeneous plasmonic layer of negative permittivity [1] or on creating multilayer structure [2] that cancels the scattering of the cloaked object (i.e., scattering cancelation technique). The technique may also be based on an inhomogeneous layer that bends electromagnetic waves around the region occupied by the cloaked object without interacting with it (i.e., transformation optics technique) [3].
TL;DR: A transformation optics (TO) based all-dielectric converging lens design comprised by a graded permittivity profile can be fabricated by additive manufacturing technology, which greatly facilitates the potential development and application of vortex wave based wireless communications.
Abstract: Radio waves carrying orbital angular momentum (OAM) may potentially increase spectrum efficiency and channel capacity based on their extra rotational degree of freedom. However, due to their divergence characteristics, vortex waves are not suitable to transmit over a long distance in the radio frequency (RF) and microwave domains. In this paper, a transformation optics (TO) based all-dielectric converging lens is proposed. The beam divergence angle of the vortex wave passing through the lens can be decreased from 25° to 9°. The transformed material parameters of the converging lens are determined by solving Laplace's equation subject to specific boundary conditions. Far-field antenna radiation patterns as well as near-field helical phase and electric field amplitude distributions obtained from numerical simulations are reported, demonstrating the broadband characteristics of the proposed microwave lens. Moreover, the all-dielectric compact lens design comprised by a graded permittivity profile can be fabricated by additive manufacturing technology, which greatly facilitates the potential development and application of vortex wave based wireless communications.
TL;DR: In this article, the authors proposed a reflectionless design of an optical waveguide coupler that is nonmagnetic and homogeneous using the linear coordinate transformation of triangles from virtual space to physical space.
Abstract: In this paper, we propose a reflectionless design of an optical waveguide coupler that is nonmagnetic and homogeneous. The coupler is designed using the linear coordinate transformation of triangles from virtual space to physical space. The common problem of reflections from the boundaries of a nonmagnetic coupler is remedied by analytically specifying the common vertex of triangles in such a way that the Jacobian matrix determinant becomes equal for all transformed triangles. The device performs ideal transmission without distorting the beam profile. We employ the effective medium theory to demonstrate the realizability of the device by using consecutive dielectric layers. We present a procedure to specify the dielectric constants of the layers from common existing optical materials. Numerical finite-element simulations confirm the functionality and the reflectionless property of the proposed designs.
TL;DR: This paper theoretically design and analyse a wide-angle optical half-wave plate by combining the field transformation (FT) approach with the form-birefringence theory and shows how the resulting medium can be mimicked by a form-fringent structure which has the same dispersion properties for a wide range of incident angles.
Abstract: In this paper, we theoretically design and analyse a wide-angle optical half-wave plate by combining the field transformation (FT) approach with the form-birefringence theory. The FT method is a general approach to manipulate electromagnetic wave propagations from pre-defined boundary conditions and artificial media by design. In theory, the approach is valid for both parallel and perpendicular polarizations. In practice, the resulting medium can be mimicked by a form-birefringent structure which has the same dispersion properties for a wide range of incident angles. A proof concept design for optical half-wave plate is designed for near-infrared operations. The transmittance of proposed device is greater than 0.8 with a polarized state change under 75° oblique incidence.
TL;DR: In this article, an impedance matching concept is implanted into transformation optics cloak to generate an impedance-matching cloak (IMC) shell, which reduces the cloaking structure's disturbance to a propagating electromagnetic field and improves its invisibility measured by scattering field intensity.
Abstract: The realization of an ideal invisible cloak implementing transformation optics is still missing. An impedance matching concept is implanted into transformation optics cloak to generate an impedance matching cloak (IMC) shell. In this work, it is proved that impedance matching structure reduces the cloaking structure's disturbance to a propagating electromagnetic field and improves its invisibility measured by scattering field intensity. Such a cylindrical IMC shell is designed, fabricated with proposed rounded rectangular split-ring-resonators (RR-SRRs), and experimental measurements show the total scattering field of a perfect electric conductor (PEC) cylinder surrounded by an IMC shell is improved greatly compared to the PEC cylinder showing electromagnetic wave front ripple suppression and a considerable scattering shrinking effect. IMC shell backward scattering field is suppressed down to 7.29%, compared to the previous value of 86.7% due to its impedance matching character, and overall scattering field intensity shrinking is down to 19.3% compared to the previously realized value of 56.4%. Sideward scattering field recorded in the experiment also has a remarkable improvement compared to the PEC cylinder. The impedance matching concept might enlighten the realization of an ideal cloak and other novel electromagnetic cloaking and shielding structures.
TL;DR: This work shows that the phase space structure of resonant modes can be revealed through the conventional Husimi functions by constructing a reciprocal virtual space for homogeneous index dielectric cavity systems.
Abstract: Dielectric cavity systems, which have been studied extensively so far, have uniform refractive indices of their cavities, and Husimi functions, the most widely used phase space representation of optical modes formed in the cavities, accordingly were derived only for these homogeneous index cavities. For the case of the recently proposed gradient index dielectric cavities (called as transformation cavities) designed by optical conformal mapping, we show that the phase space structure of resonant modes can be revealed through the conventional Husimi functions by constructing a reciprocal virtual space. As examples, the Husimi plots were obtained for an anisotropic whispering gallery mode (WGM) and a short-lived mode supported in a limacon-shaped transformation cavity. The phase space description of the corresponding modes in the reciprocal virtual space is compatible with the far-field directionality of the resonant modes in the physical space.
TL;DR: In this paper, it has been shown that nonlinearity can be incorporated into transformation optics in a consistent way, and the authors use this to illustrate a number of novel effects, including cloaking an optical soliton and modeling nonlinear solutions to Einstein's field equations.
Abstract: The advances in geometric approaches to optical devices due to transformation optics has led to the development of cloaks, concentrators, and other devices. It has also been shown that transformation optics can be used to gravitational fields from general relativity. However, the technique is currently constrained to linear devices, as a consistent approach to nonlinearity (including both the case of a nonlinear background medium and a nonlinear transformation) remains an open question. Here we show that nonlinearity can be incorporated into transformation optics in a consistent way. We use this to illustrate a number of novel effects, including cloaking an optical soliton, modeling nonlinear solutions to Einstein's field equations, controlling transport in a Debye solid, and developing a set of constitutive to relations for relativistic cloaks in arbitrary nonlinear backgrounds.
TL;DR: In this article, a series of invisibility concentrators with simplified material parameters beyond transformation optics is presented, which can achieve the perfect invisible effect at frequencies of Fabry-Perot resonances, while others have very small scattering.
Abstract: We present a series of invisibility concentrators with simplified material parameters beyond transformation optics. One of them can achieve the perfect invisible effect at frequencies of Fabry–Perot resonances, while others have very small scattering. The required materials are feasible in practice. Analytical calculations and numerical simulations confirm the functionalities of these devices.
TL;DR: In this article, a generalized design of nonmagnetic homogeneous polarization splitting devices (polarization deflector/lateral shifter) based on linear area-preserving transformations for an arbitrary incident angle was introduced.
Abstract: In this paper, we introduce the generalized design of nonmagnetic homogeneous polarization splitting devices (polarization deflector/lateral shifter) based on linear area-preserving transformations for an arbitrary incident angle. Also, by employing the Brewster angle condition, we derive a quadratic equation for principal values of the permittivity tensor that leads to the reflectionless splitting of two orthogonal polarizations for a normally impinging wave. The minimum in-plane anisotropy condition is then derived. The Brewster angle method offers significantly less anisotropy compared with the transformation optical design for larger deflection angles/lateral shifts in the normal incidence case. Finally, we show that, by using a uniaxial material (zero in-plane anisotropy), we can achieve similar functionality in the case of an obliquely incident wave. The proposed devices can separate the polarizations of the incident wave by creating a desired angle or lateral shift between TE and TM polarizations. The functionality of the proposed designs is confirmed by the commercial finite-element-based software COMSOL Multiphysics.
TL;DR: By adopting the multi-folded linear transformation optics method and its corresponding numerical techniques, this paper introduces a method to design an open cloak that has windows to exchange matter with the outer world by removing the inhomogeneity of materials and achieving cloaking functionality by anisotropic properties.
Abstract: By adopting the multi-folded linear transformation optics method and its corresponding numerical techniques, we introduce a method to design an open cloak that has windows to exchange matter with the outer world Compared with conventional remote cloaks based on inhomogeneous materials, in this paper, the inhomogeneity of materials is removed and cloaking functionality can be achieved by anisotropic properties Based on this, open-illusion devices for both active and passive scatterers have been investigated to make any emitter or object look like another pre-defined emitter or object, respectively The proposed devices have perfect performance with an object-independent feature for moving objects in particular The proposed devices will open up possibilities and be useful for practical implementations of the cloak and illusion optics technologies that were recently developed
TL;DR: In this paper, a method is proposed that utilizes three-dimensional finite-difference time-domain simulations of light propagation for restoring the effective Kerr nonlinearity of nanocomposite media.
Abstract: In this Letter, a method is proposed that utilizes three-dimensional finite-difference time-domain simulations of light propagation for restoring the effective Kerr nonlinearity of nanocomposite media. In this approach, a dependence of the phase shift of the transmitted light on the input irradiance is exploited. The reconstructed values of the real parts of the nonlinear refractive index of a structure of randomly arranged spheres are in good agreement with the predictions of the effective medium approximations.
TL;DR: In this paper, a metamaterial unit cell with single-gap Split Ring Resonator (SRR) was modified and the effect of these changes on its electromagnetic properties was examined.
Abstract: Some geometric parameters of a metamaterial unit cell with single-gap Split Ring Resonator (SRR) are modified and the effect of these changes on its electromagnetic properties is examined. In particular, the relative magnetic permeability has been investigated. For unit cells with various geometric parameters the frequency fp in which the relative magnetic permeability is close to zero as well as the resonance frequency f0 are obtained. Finally, as an example, for each of the unit cells, the relative magnetic permeability at 9.5 GHz is obtained and by using these results an electromagnetic invisibility cloak is designed operating at 9.5 GHz which can has three different unit cells with different geometric parameters for each of its layers.