Showing papers on "Transformation optics published in 2010"
TL;DR: A three-dimensional invisibility-cloaking structure operating at optical wavelengths based on transformation optics is designed and realized and uses a woodpile photonic crystal with a tailored polymer filling fraction to hide a bump in a gold reflector.
Abstract: We have designed and realized a three-dimensional invisibility-cloaking structure operating at optical wavelengths based on transformation optics. Our blueprint uses a woodpile photonic crystal with a tailored polymer filling fraction to hide a bump in a gold reflector. We fabricated structures and controls by direct laser writing and characterized them by simultaneous high-numerical-aperture, far-field optical microscopy and spectroscopy. A cloaking operation with a large bandwidth of unpolarized light from 1.4 to 2.7 micrometers in wavelength is demonstrated for viewing angles up to 60 degrees.
1,141 citations
TL;DR: The potential of transformation optics to create functionalities in which the optical properties can be designed almost at will is reviewed, which can be used to engineer various optical illusion effects, such as the invisibility cloak.
Abstract: Transformation optics describes the capability to design the path of light waves almost at will through the use of metamaterials that control effective materials properties on a subwavelength scale. In this review, the physics and applications of transformation optics are discussed.
1,085 citations
TL;DR: It is experimentally demonstrated that the incorporation of gain material in the high-local-field areas of a metamaterial makes it possible to fabricate an extremely low-loss and active optical NIM.
Abstract: Much research activity is being devoted to the design and fabrication of metamaterials, artificially tailored composites with the counter-intuitive optical property of a negative refraction index. There is an exciting and wide range of possible applications that could be developed with such negative-index materials, including invisibility cloaks and 'perfect' lenses, but a major hurdle is that the performance is severely limited by absorption losses. Vladimir Shalaev and colleagues now demonstrate an approach that could lead to a breakthrough in this area; they have incorporated an optical gain medium within the metamaterial as a way to compensate the intrinsic loss, and show that optical pumping leads to a significantly improved negative refraction index and performance-related figure-of-merit at visible wavelengths. The study confirms that it is possible to design an optical metamaterial that is not limited by the intrinsic loss of its metal constituent. Metamaterials have the counterintuitive optical property of negative refraction index. They have a wide range of possible applications, including 'invisibility cloaks' and perfect lenses, but their performance is severely limited by absorption losses. These authors have incorporated an optical gain medium within a metamaterial as a way to compensate the intrinsic loss, and show that optical pumping leads to a significantly improved negative refraction index and figure of merit within the 722–738-nm visible wavelength range. The recently emerged fields of metamaterials and transformation optics promise a family of exciting applications such as invisibility, optical imaging with deeply subwavelength resolution and nanophotonics with the potential for much faster information processing. The possibility of creating optical negative-index metamaterials (NIMs) using nanostructured metal–dielectric composites has triggered intense basic and applied research over the past several years1,2,3,4,5,6,7,8,9,10. However, the performance of all NIM applications is significantly limited by the inherent and strong energy dissipation in metals, especially in the near-infrared and visible wavelength ranges11,12. Generally the losses are orders of magnitude too large for the proposed applications, and the reduction of losses with optimized designs seems to be out of reach. One way of addressing this issue is to incorporate gain media into NIM designs13,14,15,16. However, whether NIMs with low loss can be achieved has been the subject of theoretical debate17,18. Here we experimentally demonstrate that the incorporation of gain material in the high-local-field areas of a metamaterial makes it possible to fabricate an extremely low-loss and active optical NIM. The original loss-limited negative refractive index and the figure of merit (FOM) of the device have been drastically improved with loss compensation in the visible wavelength range between 722 and 738 nm. In this range, the NIM becomes active such that the sum of the light intensities in transmission and reflection exceeds the intensity of the incident beam. At a wavelength of 737 nm, the negative refractive index improves from −0.66 to −1.017 and the FOM increases from 1 to 26. At 738 nm, the FOM is expected to become macroscopically large, of the order of 106. This study demonstrates the possibility of fabricating an optical negative-index metamaterial that is not limited by the inherent loss in its metal constituent.
745 citations
TL;DR: The design, realization and measurement of a three-dimensional approximate transformation-optics lens in the microwave frequency band is shown, made of non-resonant metamaterials, which are fabricated with multilayered dielectric plates by drilling inhomogeneous holes.
Abstract: Lenses with superior performance with respect to conventional uniform materials are desirable. The authors show a three-dimensional lens, made of multilayered metamaterials and based on approximate transformation optics, which works in different polarizations at broad viewing angles and with wide bandwidth.
417 citations
TL;DR: In this article, the authors give a brief introduction to the application of the new technique of transformation acoustics, which draws on a correspondence between coordinate transformation and material properties and is formulated for both acoustic waves and linear liquid surface waves.
Abstract: In this review, we give a brief introduction to the application of the new technique of transformation acoustics, which draws on a correspondence between coordinate transformation and material properties The technique is formulated for both acoustic waves and linear liquid surface waves Some interesting conceptual devices can be designed for manipulating acoustic waves For example, we can design acoustic cloaks that make an object invisible to acoustic waves, and the cloak can either encompass or lie outside the object to be concealed Transformation acoustics, as an analog of transformation optics, can go beyond invisibility cloaking As an illustration for manipulating linear liquid surface waves, we show that a liquid wave rotator can be designed and fabricated to rotate the wave front The acoustic transformation media require acoustic materials which are anisotropic and inhomogeneous Such materials are difficult to find in nature However, composite materials with embedded sub-wavelength resonators can in principle be made and such 'acoustic metamaterials' can exhibit nearly arbitrary values of effective density and modulus tensors to satisfy the demanding material requirements in transformation acoustics We introduce resonant sonic materials and Helmholtz resonators as examples of acoustic metamaterials that exhibit resonant behaviour in effective density and effective modulus
350 citations
TL;DR: The intricate interplay between different coupling effects in a plasmon hybridization picture provides a useful tool to intuitively understand the evolution from molecule-like states to solid-state-like bands.
Abstract: Metamaterials have become one of the hottest fields of photonics since the pioneering work of John Pendry on negative refractive index, invisibility cloaking, and perfect lensing. Three-dimensional metamaterials are required for practical applications. In these materials, coupling effects between individual constituents play a dominant role for the optical and electronic properties. Metamaterials can show both electric and magnetic responses at optical frequencies. Thus, electric as well as magnetic dipolar and higher-order multipolar coupling is the essential mechanism. Depending on the structural composition, both longitudinal and transverse coupling occur. The intricate interplay between different coupling effects in a plasmon hybridization picture provides a useful tool to intuitively understand the evolution from molecule-like states to solid-state-like bands.
292 citations
Book•
18 Oct 2010TL;DR: Transformation optics as mentioned in this paper is an area with applications ranging from invisibility and perfect imaging to the quantum physics of black holes and has been a subject of fiction for millennia, from myths of the ancient Greeks and Germans to modern novels and films.
Abstract: Summary form only given Science Magazine listed transformation optics among the top 10 science insights of the decade 2000-2010 The tutorial gives an introduction into this subject that may, literally, transform optics Transformation optics grew out of ideas for invisibility cloaking devices and exploits connections between electromagnetism in media and in geometries Within a short time it grew into a lively research area with applications ranging from invisibility and perfect imaging to the quantum physics of black holes Invisibility has been a subject of fiction for millennia, from myths of the ancient Greeks and Germans to modern novels and films In 2006 invisibility turned from fiction into science, primarily initiated by the publication of first ideas for cloaking devices and the subsequent demonstration of cloaking for microwaves Perfect imaging is the ability to optically transfer images with a resolution not limited by the wave nature of light Advances in imaging are of significant importance to modern electronics, because the structures of microchips are made by photolithography; in order to make smaller structures, light with increasingly smaller wavelength is used, which is increasingly difficult Black holes are surrounded by horizons that create quantum particles from the virtual particles of the quantum vacuum, Hawking radiation Understanding and testing this mysterious phenomenon will shed light on connections between quantum physics and general relativity The common root of invisibility, perfect imaging and the physics of horizons is the fact that optical media act as effective geometries: they appear to change the measure of space and time The tutorial will explain this connection between geometry and light and show how it can be applied in optics
290 citations
TL;DR: In this article, the authors reported the first experimental demonstration of an omnidirectional electromagnetic absorber in the microwave frequency, composed of non-resonant and resonant metamaterial structures, which can trap and absorb electromagnetic waves coming from all directions spirally inwards without any reflections due to the local control of electromagnetic fields.
Abstract: In a recent theoretical work by Narimanov and Kildishev (2009 Appl. Phys. Lett. 95 041106) an optical omnidirectional light absorber based on metamaterials was proposed, in which theoretical analysis and numerical simulations showed that all optical waves hitting the absorber are trapped and absorbed. Here we report the first experimental demonstration of an omnidirectional electromagnetic absorber in the microwave frequency. The proposed device is composed of non-resonant and resonant metamaterial structures, which can trap and absorb electromagnetic waves coming from all directions spirally inwards without any reflections due to the local control of electromagnetic fields. It is shown that the absorption rate can reach 99 per cent in the microwave frequency. The all-directional full absorption property makes the device behave like an 'electromagnetic black body', and the wave trapping and absorbing properties simulate, to some extent, an 'electromagnetic black hole.' We expect that such a device could be used as a thermal emitting source and to harvest electromagnetic waves.
267 citations
TL;DR: This work shows that the propagation of SPPs can be manipulated in a prescribed manner by careful control of the dielectric material properties adjacent to a metal, providing a practical way for routing light at very small scales.
Abstract: We propose and demonstrate efficiently molding surface plasmon polaritons (SPPs) based on transformation optics. SPPs are surface modes of electromagnetic waves tightly bound at metal-dielectric interfaces, which allow us to scale optics beyond the diffraction limit. Taking advantage of transformation optics, here we show that the propagation of SPPs can be manipulated in a prescribed manner by careful control of the dielectric material properties adjacent to a metal. Since the metal properties are completely unaltered, this methodology provides a practical way for routing light at very small scales. For instance, our approach enables SPPs to travel at uneven and curved surfaces over a broad wavelength range, where SPPs would normally suffer significant scattering losses. In addition, a plasmonic 180° waveguide bend and a plasmonic Luneburg lens with simple designs are presented. The unique design flexibility of the transformational plasmon optics introduced here may open a new door to nano optics and downscaling of photonic circuits.
244 citations
TL;DR: The general methodology for the design of transformation optical devices for surface plasmons is described and three representative examples with different functionalities are analyzed: a beam shifter, a cylindrical cloak, and a ground-plane cloak.
Abstract: A new strategy to control the flow of surface plasmon polaritons at metallic surfaces is presented. It is based on the application of the concept of transformation optics to devise the optical parameters of the dielectric medium placed on top of the metal surface. We describe the general methodology for the design of transformation optical devices for surface plasmons and analyze, for proof-of-principle purposes, three representative examples with different functionalities: a beam shifter, a cylindrical cloak, and a ground-plane cloak.
231 citations
TL;DR: In this article, an overview of transformation-electromagnetic device design techniques is presented, starting with electromagnetic cloaks that have spherical shell or cylindrical annular shapes, more general cloaking designs of noncircular annular geometries are treated, and the application of cloaking to RF/microwave antenna shielding is also discussed.
Abstract: The recently introduced transformation-electromagnetics techniques provide a new methodology for designing devices that possess novel wave-material interaction properties. They are based on the form invariance of Maxwell's equations under coordinate transformations. These methods provide an extremely versatile set of design tools that employ spatial-coordinate transformations, where the compression and dilation of space in different coordinate directions are interpreted as appropriate scalings of the material parameters. The most famous transformation-optics device is the cloak of invisibility. However, a wide variety of other devices are also possible, such as field concentrators, polarization rotators, beam splitters, beam collimators, and flat lenses. In this paper, an overview of transformation-electromagnetics device design techniques is presented. The paper begins by introducing the underlying design principle behind transformation electromagnetics. Several novel transformation-based device designs are then summarized, starting with electromagnetic cloaks that have spherical shell or cylindrical annular shapes, More general cloaking designs of noncircular annular geometries are treated, and the application of cloaking to RF/microwave antenna shielding is also discussed. Following this, device designs that employ transformations that have discontinuities .on the domain boundary are presented. Unlike those used for cloaks, this type of transformation is capable of modifying the fields outside of the device. Examples of this type of transformation-electromagnetics device are presented, which include flat near-field and far-field focusing lenses, wave collimators for embedded sources (e.g., antennas), polarization splitters and rotators, and right-angle beam benders.
TL;DR: Here, a simple and robust method to retrieve the effective constitutive parameters for chiral metamaterials is urgently needed and it is found that the substrate may cause the homogeneous slab to be inhomogeneous, i.e. the reflections in forward and backward directions are different.
Abstract: After the prediction that strong enough optical activity may result in negative refraction and negative reflection, more and more artificial chiral metamaterials were designed and fabricated at difference frequency ranges from microwaves to optical waves. Therefore, a simple and robust method to retrieve the effective constitutive parameters for chiral metamaterials is urgently needed. Here, we analyze the wave propagation in chiral metamaterials and follow the regular retrieval procedure for ordinary metamaterials and apply it in chiral metamaterial slabs. Then based on the transfer matrix technique, the parameter retrieval is extended to treat samples with not only the substrate but also the top layers. After the parameter retrieval procedure, we take two examples to check our method and study how the substrate influences on the thin chiral metamaterials slabs. We find that the substrate may cause the homogeneous slab to be inhomogeneous, i.e. the reflections in forward and backward directions are different. However, the chiral metamaterial where the resonance element is embedded far away from the substrate is insensitive to the substrate.
TL;DR: In this paper, a broadband gigahertz region metamaterial absorber with a maximum absorption of 99.9% at 2.4 GHz and a full width at half maximum bandwidth of 700 MHz, all while maintaining low reflection inside and outside of resonance.
Abstract: Artificially engineered metamaterials have enabled the creation of electromagnetic materials with properties not found in nature. Recent work has demonstrated the feasibility of developing high performance, narrowband electromagnetic absorbers using such metamaterials. These metamaterials derive their absorption properties primarily through dielectric loss and impedance matching at resonance. This paper builds on that work by increasing the bandwidth through embedding resistors into the metamaterial structure in order to lower the Q factor and by using multiple elements with different resonances. This is done while maintaining an impedance-matched material at normal incidence. We thus present the design, simulation, and experimental verification of a broadband gigahertz region metamaterial absorber, with a maximum absorption of 99.9% at 2.4 GHz, and a full width at half maximum bandwidth of 700 MHz, all while maintaining low reflection inside and outside of resonance.
TL;DR: Temperature-dependent transmission in the millimeter-wave part of the spectrum in high-Tc superconducting cuprate metamaterials supporting sub-radiant resonances of Fano type is demonstrated.
Abstract: Losses are the main evil that limits the use of metamaterials in practical applications. While radiation losses may be controlled by design, Joule losses are hereditary to the metamaterial structures. An exception is superconducting metamaterials, where Joule losses can be uniquely controlled with temperature in a very wide range. We put this in use by demonstrating temperature-dependent transmission in the millimeter-wave part of the spectrum in high-Tc superconducting cuprate metamaterials supporting sub-radiant resonances of Fano type.
TL;DR: Numerical simulations of the graded photonic crystal based Luneburg lens and electromagnetic beam bend show that the homogenization based on Maxwell-Garnett theory gives very good results for implementation of devices intended to steer and focus electromagnetic fields.
Abstract: Engineering of a refractive index profile is a powerful method for controlling electromagnetic fields. In this paper, we investigate possible realization of isotropic gradient refractive index media at optical frequencies using two-dimensional graded photonic crystals. They consist of dielectric rods with spatially varying radii and can be homogenized in broad frequency range within the lowest band. Here they operate in metamaterial regime, that is, the graded photonic crystals are described with spatially varying effective refractive index so they can be regarded as low-loss and broadband graded dielectric metamaterials. Homogenization of graded photonic crystals is done with Maxwell-Garnett effective medium theory. Based on this theory, the analytical formulas are given for calculations of the rods radii which makes the implementation straightforward. The frequency range where homogenization is valid and where graded photonic crystal based devices work properly is discussed in detail. Numerical simulations of the graded photonic crystal based Luneburg lens and electromagnetic beam bend show that the homogenization based on Maxwell-Garnett theory gives very good results for implementation of devices intended to steer and focus electromagnetic fields.
TL;DR: In this article, the frequency-dependent elements of the effective permittivity and permeability tensors for arbitrary angles of incidence were retrieved for the fishnet metamaterial and it was shown that genuine effective material parameters can only be introduced if quite stringent constraints are imposed on the wavelength/unit cell size ratio.
Abstract: Although optical metamaterials that show artificial magnetism are mesoscopic systems, they are frequently described in terms of effective material parameters. But due to intrinsic nonlocal (or spatially dispersive) effects it may be anticipated that this approach is usually only a crude approximation and is physically meaningless. In order to study the limitations regarding the assignment of effective material parameters, we present a technique to retrieve the frequency-dependent elements of the effective permittivity and permeability tensors for arbitrary angles of incidence and apply the method exemplarily to the fishnet metamaterial. It turns out that for the fishnet metamaterial, genuine effective material parameters can only be introduced if quite stringent constraints are imposed on the wavelength/unit cell size ratio. Unfortunately they are only met far away from the resonances that induce a magnetic response required for many envisioned applications of such a fishnet metamaterial. Our work clearly indicates that the mesoscopic nature and the related spatial dispersion of contemporary optical metamaterials that show artificial magnetism prohibits the meaningful introduction of conventional effective material parameters.
TL;DR: The transformation optics was applied to mimic a black hole of Schwarzschild form and similar properties of photon sphere were also found numerically for the metamaterial black hole.
Abstract: We applied the transformation optics to mimic a black hole of Schwarzschild form. Similar properties of photon sphere were also found numerically for the metamaterial black hole. Several reduced versions of the black hole systems were proposed for easier implementations.
TL;DR: A powerful theoretical tool reveals the broadband response and superfocusing properties of touching metal nanospheres and provides an elegant physical description of the prominent field enhancement that takes place at the point of contact between a spherical nanoparticle and a flat metallic surface.
Abstract: A general three-dimensional transformation optics approach is presented that yields analytical expressions for the relevant electromagnetic magnitudes in plasmonic phenomena at singular geometries. This powerful theoretical tool reveals the broadband response and superfocusing properties of touching metal nanospheres and provides an elegant physical description of the prominent field enhancement that takes place at the point of contact between a spherical nanoparticle and a flat metallic surface.
TL;DR: This paper defines three spatial coordinate transformations which show the possibility of designing a taper between two different waveguides and proposes achievable values of permittivity and permeability that can be obtained with existing metamaterials.
Abstract: Spatial coordinate transformation is a suitable tool for the design of complex electromagnetic structures. In this paper, we define three spatial coordinate transformations which show the possibility of designing a taper between two different waveguides. A parametric study is presented for the three transformations and we propose achievable values of permittivity and permeability that can be obtained with existing metamaterials. The performances of such defined structures are demonstrated by finite element numerical simulations.
TL;DR: It is concluded that the design of metamaterials with tailored simultaneous electric and magnetic response-such as negative index materials-will generally be complicated by potentially unwanted magnetoelectric coupling.
Abstract: Electromagnetic metamaterials are artificially structured media typically composed of arrays of resonant electromagnetic circuits, the dimension and spacing of which are considerably smaller than the free-space wavelengths of operation. The constitutive parameters for metamaterials, which can be obtained using full-wave simulations in conjunction with numerical retrieval algorithms, exhibit artifacts related to the finite size of the metamaterial cell relative to the wavelength. Liu [R. Liu, T. J. Cui, D. Huang, B. Zhao, and D. R. Smith, Phys. Rev. E 76, 026606 (2007)] showed that the complicated, frequency-dependent forms of the constitutive parameters can be described by a set of relatively simple analytical expressions. These expressions provide useful insight and can serve as the basis for more intelligent interpolation or optimization schemes. Here, we show that the same analytical expressions can be obtained using a transfer-matrix formalism applied to a one-dimensional periodic array of thin, resonant, dielectric, or magnetic sheets. The transfer-matrix formalism breaks down, however, when both electric and magnetic responses are present in the same unit cell, as it neglects the magnetoelectric coupling between unit cells [C. R. Simovski, Metamaterials 1, 62 (2007)]. We show that an alternative analytical approach based on the same physical model must be applied for such structures. Furthermore, in addition to the intercell coupling, electric and magnetic resonators within a unit cell may also exhibit magnetoelectric coupling. For such cells, we find an analytical expression for the effective index, which displays markedly characteristic dispersion features that depend on the strength of the coupling coefficient. We illustrate the applicability of the derived expressions by comparing to full-wave simulations on magnetoelectric unit cells. We conclude that the design of metamaterials with tailored simultaneous electric and magnetic response-such as negative index materials-will generally be complicated by potentially unwanted magnetoelectric coupling.
TL;DR: It is demonstrated that restricting the spatial transformation to a conformal mapping can lead to much simpler material parameters for more practical implementation of transformation optics devices.
Abstract: The transformation optics technique for designing novel electromagnetic and optical devices offers great control over wave behavior, but is difficult to implement primarily due to limitations in current metamaterial design and fabrication techniques. This paper demonstrates that restricting the spatial transformation to a conformal mapping can lead to much simpler material parameters for more practical implementation. As an example, a flat cylindrical-to-plane-wave conversion lens is presented and its performance validated through numerical simulations. It is shown that the lens dimensions and embedded source location can be adjusted to produce one, two, or four highly directive planar beams. Two metamaterial designs for this lens that implement the required effective medium parameters are proposed and their behavior analyzed.
TL;DR: In this paper, the authors proposed a class of optical transformation media, illusion media, which render the enclosed object invisible and generate one or more virtual objects as desired, and applied the proposed media to design a microwave device, which transforms an actual object into two virtual objects.
Abstract: We propose a class of optical transformation media, illusion media, which render the enclosed object invisible and generate one or more virtual objects as desired. We apply the proposed media to design a microwave device, which transforms an actual object into two virtual objects. Such an illusion device exhibits unusual electromagnetic behavior as verified by full-wave simulations. Different from the published illusion devices which are composed of left-handed materials with simultaneously negative permittivity and permeability, the proposed illusion media have finite and positive permittivity and permeability. Hence the designed device could be realizable using artificial metamaterials.
TL;DR: In this article, a terahertz metamaterial with wire diameters down to ∼10μm and lattice constants of ∼100μm was constructed using drawing.
Abstract: Electromagnetic metamaterials attract much attention since they can be engineered to exhibit optical properties not found in nature. Their fabrication, however, is challenging, especially in volume. We introduce drawing as a means of fabricating metamaterials, thus demonstrating a terahertz metamaterial. We codraw polymethyl-methacrylate and indium, producing several meters of metamaterial with wire diameters down to ∼10 μm, and lattice constants of ∼100 μm. We experimentally characterize the transmission properties of different samples, observing high-pass filtering between 0.3–0.4 THz, in good agreement with simulations.
TL;DR: An approximate tensor analysis of the proposed metamaterials is first developed in this article, which is then used to verify the approximate analysis and derive exact dispersion equations and impedance relations.
Abstract: Transmission-line (TL) metamaterials possessing effective material parameters that are diagonal in the Cartesian basis have been previously studied. In this paper, TL metamaterials with arbitrary full tensors are introduced and analyzed. An approximate tensor analysis of the proposed metamaterials is first developed. Bloch analysis is then used to verify the approximate analysis and derive exact dispersion equations and impedance relations. Finally, simulation results are presented that validate the analysis and show the utility of this new class of metamaterials. The ability to design tensor metamaterials such as these is crucial to the practical implementation of novel devices derived through transformational optics/electromagnetics.
TL;DR: In this paper, a gradient index metamaterial (GIMM) was proposed for the design of cloaks, various lenses, beam shifters and beam-steering devices.
Abstract: Gradient index metamaterials have wide applications in the microwave and optical fields. Based on the quasi-static theory, such materials at the microwave band have been realized by drilling hole arrays on ordinary dielectric materials. As applications of the gradient index metamaterials, novel devices including a 45° dielectric wave-bending structure, a 16° wave-steering lens and a microwave focusing lens are designed and fabricated. Field mapping measurements validate the proposed gradient index metamaterials and the device designs. The method can be directly and easily extended to the design of cloaks, various lenses, beam shifters and beam-steering devices. It can also be applied in the optical band as long as quasi-static conditions are satisfied. The method and the devices may find applications in integrated circuit systems.
TL;DR: A transformation optics design approach together with an experimental demonstration that takes advantage of this dimensionality by integrating multiple, independent optical elements into a single optical Janus or metadevice.
Abstract: In Roman mythology, the god Janus was depicted with two faces, looking in opposite directions. This led to the phrase ‘‘Janus faced’’ which is mostly used for a ‘‘two-faced’’ or deceitful character of a person. Within integrated photonics a concept like Janus can provide a new class of multi-functional optical meta-elements which could be a key ingredient in achieving compact and high speed photonic systems. While therehave been great strides in the miniaturization of optical elements, such photonic integration largely consists of combining discrete components at the chip level. Here, we present a new approach of designing a single optical element that possesses simultaneously multiple distinct functions. We employ transformation optics to design the optical space and manipulate the light propagation using a metamaterial with spatially varying permittivity. Our experiment demonstrates a single optical ‘‘Janus’’ device that acts as a lens as well as a beam-shifter at the same time. The emerging field of transformation optics has provided a new design methodology allowing an unprecedented manipulation of light propagation, with the optical cloak as the most prominent example. [1,2] However, transformation optics can also be used to enhance the functionality of conventional optical elements. Traditionally, these conventional elements only involve stretching or compressing the optical space in one direction whereas the remaining dimensions in space are unaltered. For example, an optical lens can be interpreted as a result of a simple wavefront transformation that molds the flow of light in a particular direction. A lens works well in one direction whereas light propagating perpendicular to this direction is strongly perturbed. Since space can be modified in two or three dimensions simultaneously, the additional degrees of freedom provided by transformation optics can be used to spatially imprint elements into a single optical Janus or metadevice. Here, we present a transformation optics design approach together with an experimental demonstration that takes advantage of this dimensionality by integrating multiple, independent optical
TL;DR: This work shows that it can harness surface plasmon polaritons at a metal surface structured with a dielectric material to obtain a unique control of their propagation and demonstrate invisibility over an unprecedented bandwidth.
Abstract: One of the key challenges in current research into electromagnetic cloaking is to achieve invisibility at optical frequencies and over an extended bandwidth. There has been significant progress towards this using the idea of cloaking by sweeping under the carpet of Li and Pendry. Here, we show that we can harness surface plasmon polaritons at a metal surface structured with a dielectric material to obtain a unique control of their propagation. We exploit this control to demonstrate both theoretically and experimentally cloaking over an unprecedented bandwidth (650-900 nm). Our non-resonant plasmonic metamaterial is designed using transformational optics extended to plasmonics and allows a curved reflector to mimic a flat mirror. Our theoretical predictions are validated by experiments mapping the surface light intensity at a wavelength of 800 nm.
TL;DR: In this paper, a conformal mapping technique is used to take advantage of conformal alignment for various optical elements such as directional antennas, flat lenses, or bends. And the authors show that these elements can be implemented with isotropic materials, thus strongly facilitating their fabrication, and furthermore generalize the concept and show that under certain conditions previously suggested devices consisting of anisotropic materials may be replaced by isotropics using an appropriate transformation.
Abstract: By taking advantage of a conformal mapping technique, we propose designs for various optical elements such as directional antennas, flat lenses, or bends. In contrast to most of the existing design approaches, the elements can be implemented with isotropic materials, thus strongly facilitating their fabrication. We furthermore generalize the concept and show that under certain conditions previously suggested devices consisting of anisotropic materials may be replaced by isotropic ones using an appropriate transformation. The designs are double-checked by full-wave simulations. A comparison with their anisotropic counterparts reveals a similar performance.
TL;DR: A level-set based topology optimization method, in which the interface between the vacuum and metal phases is implicitly expressed by the zero-level contour of a higher dimensionallevel-set function, which maximizes the objective based on the normal direction of the level- set function and induced current flow, thereby generating the desirable patterns of current flow on metal surface.
Abstract: Achieving negative permittivity and negative permeability signifies a key topic of research in the design of metamaterials. This paper introduces a level-set based topology optimization method, in which the interface between the vacuum and metal phases is implicitly expressed by the zero-level contour of a higher dimensional level-set function. Following a sensitivity analysis, the optimization maximizes the objective based on the normal direction of the level-set function and induced current flow, thereby generating the desirable patterns of current flow on metal surface. As a benchmark example, the U-shaped structure and its variations are obtained from the level-set topology optimization. Numerical examples demonstrate that both negative permittivity and negative permeability can be attained.
TL;DR: A coordinate transformation is applied to flatten a Maxwell fish-eye lens, forming a near-perfect relay lens, and also flatten the focal surface associated with a conventional refractive lens, such that the system exhibits an ultra-wide field-of-view with reduced aberration.
Abstract: We apply the transformation optical technique to modify or improve conventional refractive and gradient index optical imaging devices. In particular, when it is known that a detector will terminate the paths of rays over some surface, more freedom is available in the transformation approach, since the wave behavior over a large portion of the domain becomes unimportant. For the analyzed configurations, quasi-conformal and conformal coordinate transformations can be used, leading to simplified constitutive parameter distributions that, in some cases, can be realized with isotropic index; index-only media can be low-loss and have broad bandwidth. We apply a coordinate transformation to flatten a Maxwell fish-eye lens, forming a near-perfect relay lens; and also flatten the focal surface associated with a conventional refractive lens, such that the system exhibits an ultra-wide field-of-view with reduced aberration.