Using the freedom of design that metamaterials provide, we show how electromagnetic fields can be redirected at will and propose a design strategy. The conserved fields-electric displacement field D, magnetic induction field B, and Poynting vector B-are all displaced in a consistent manner. A simple illustration is given of the cloaking of a proscribed volume of space to exclude completely all electromagnetic fields. Our work has relevance to exotic lens design and to the cloaking of objects from electromagnetic fields.

/pdf/controlling-electromagnetic-fields-3ryxkryf1t.pdf

Controlling Electromagnetic Fields

Fundamentals of Plasmonics.- Electromagnetics of Metals.- Surface Plasmon Polaritons at Metal / Insulator Interfaces.- Excitation of Surface Plasmon Polaritons at Planar Interfaces.- Imaging Surface Plasmon Polariton Propagation.- Localized Surface Plasmons.- Electromagnetic Surface Modes at Low Frequencies.- Applications.- Plasmon Waveguides.- Transmission of Radiation Through Apertures and Films.- Enhancement of Emissive Processes and Nonlinearities.- Spectroscopy and Sensing.- Metamaterials and Imaging with Surface Plasmon Polaritons.- Concluding Remarks.

/pdf/plasmonics-fundamentals-and-applications-4syb9877sr.pdf

Plasmonics: Fundamentals and Applications

The unprecedented ability of nanometallic (that is, plasmonic) structures to concentrate light into deep-subwavelength volumes has propelled their use in a vast array of nanophotonics technologies and research endeavours. Plasmonic light concentrators can elegantly interface diffraction-limited dielectric optical components with nanophotonic structures. Passive and active plasmonic devices provide new pathways to generate, guide, modulate and detect light with structures that are similar in size to state-of-the-art electronic devices. With the ability to produce highly confined optical fields, the conventional rules for light-matter interactions need to be re-examined, and researchers are venturing into new regimes of optical physics. In this review we will discuss the basic concepts behind plasmonics-enabled light concentration and manipulation, make an attempt to capture the wide range of activities and excitement in this area, and speculate on possible future directions.

/pdf/plasmonics-for-extreme-light-concentration-and-manipulation-25m55spiva.pdf

Plasmonics for extreme light concentration and manipulation.

The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

Plasmons in strongly coupled metallic nanostructures.

Artificially structured metamaterials have enabled unprecedented flexibility in manipulating electromagnetic waves and producing new functionalities, including the cloak of invisibility based on coordinate transformation1,2,3. Unlike other cloaking approaches4,5,6, which are typically limited to subwavelength objects, the transformation method allows the design of cloaking devices that render a macroscopic object invisible. In addition, the design is not sensitive to the object that is being cloaked. The first experimental demonstration of such a cloak at microwave frequencies was recently reported7. We note, however, that that design7 cannot be implemented for an optical cloak, which is certainly of particular interest because optical frequencies are where the word ‘invisibility’ is conventionally defined. Here we present the design of a non-magnetic cloak operating at optical frequencies. The principle and structure of the proposed cylindrical cloak are analysed, and the general recipe for the implementation of such a device is provided.

/pdf/optical-cloaking-with-metamaterials-44hn07kw9x.pdf

Optical cloaking with metamaterials

A double-periodic array of pairs of parallel gold nanorods is shown to have a negative refractive index in the optical range. Such behavior results from the plasmon resonance in the pairs of nanorods for both the electric and the magnetic components of light. The refractive index is retrieved from direct phase and amplitude measurements for transmission and reflection, which are all in excellent agreement with simulations. Both experiments and simulations demonstrate that a negative refractive index n???0.3 is achieved at the optical communication wavelength of 1.5??m using the array of nanorods. The retrieved refractive index critically depends on the phase of the transmitted wave, which emphasizes the importance of phase measurements in finding n?.

http://cds.cern.ch/record/832707/files/0504091.pdf

Negative index of refraction in optical metamaterials.

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.

https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1686&context=nanopub

Loss-free and active optical negative-index metamaterials

In an electromagnetic cloak based on a transformation approach, reduced sets of material properties are generally favored due to their easier implementation in reality, although a seemingly inevitable drawback of undesired scattering exists in such cloaks. Here, the authors suggest the use of high-order transformations to create smooth moduli at the outer boundary of the cloak, therefore completely eliminating the detrimental scattering within the limit of geometric optics. The authors apply this scheme to a nonmagnetic cylindrical cloak and demonstrate that the scattered field is reduced substantially in a cloak with optimal quadratic transformation as compared to its linear counterpart.

/pdf/nonmagnetic-cloak-with-minimized-scattering-1thkgdvk64.pdf

Nonmagnetic cloak with minimized scattering

A family of coupled nanostrips with varying dimensions is demonstrated exhibiting optical magnetic responses across the whole visible spectrum, from red to blue. We refer to such a phenomenon as rainbow magnetism. The experimental and analytical studies of such structures provide us with a universal building block and a general recipe for producing controllable optical magnetism for various practical implementations.

/pdf/metamagnetics-with-rainbow-colors-5249xps7xb.pdf

Uday K. Chettiar

Papers

Optical cloaking with metamaterials

Negative index of refraction in optical metamaterials.

Loss-free and active optical negative-index metamaterials

Nonmagnetic cloak with minimized scattering

Metamagnetics with rainbow colors.