There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

We present the design for an absorbing metamaterial (MM) with near unity absorbance A(omega). Our structure consists of two MM resonators that couple separately to electric and magnetic fields so as to absorb all incident radiation within a single unit cell layer. We fabricate, characterize, and analyze a MM absorber with a slightly lower predicted A(omega) of 96%. Unlike conventional absorbers, our MM consists solely of metallic elements. The substrate can therefore be optimized for other parameters of interest. We experimentally demonstrate a peak A(omega) greater than 88% at 11.5 GHz.

Perfect metamaterial absorber.

Metamaterials are artificially fabricated materials that allow for the control of light and acoustic waves in a manner that is not possible in nature. This Review covers the recent developments in the study of so-called metasurfaces, which offer the possibility of controlling light with ultrathin, planar optical components. Conventional optical components such as lenses, waveplates and holograms rely on light propagation over distances much larger than the wavelength to shape wavefronts. In this way substantial changes of the amplitude, phase or polarization of light waves are gradually accumulated along the optical path. This Review focuses on recent developments on flat, ultrathin optical components dubbed 'metasurfaces' that produce abrupt changes over the scale of the free-space wavelength in the phase, amplitude and/or polarization of a light beam. Metasurfaces are generally created by assembling arrays of miniature, anisotropic light scatterers (that is, resonators such as optical antennas). The spacing between antennas and their dimensions are much smaller than the wavelength. As a result the metasurfaces, on account of Huygens principle, are able to mould optical wavefronts into arbitrary shapes with subwavelength resolution by introducing spatial variations in the optical response of the light scatterers. Such gradient metasurfaces go beyond the well-established technology of frequency selective surfaces made of periodic structures and are extending to new spectral regions the functionalities of conventional microwave and millimetre-wave transmit-arrays and reflect-arrays. Metasurfaces can also be created by using ultrathin films of materials with large optical losses. By using the controllable abrupt phase shifts associated with reflection or transmission of light waves at the interface between lossy materials, such metasurfaces operate like optically thin cavities that strongly modify the light spectrum. Technology opportunities in various spectral regions and their potential advantages in replacing existing optical components are discussed.

Flat Optics With Designer Metasurfaces

Plasmons describe collective oscillations of electrons. They have a fundamental role in the dynamic responses of electron systems and form the basis of research into optical metamaterials 1–3 . Plasmons of two-dimensional massless electrons, as present in graphene, show unusual behaviour 4–7 that enables new tunable plasmonic metamaterials 8–10 and, potentially, optoelectronic applications in the terahertz frequency range 8,9,11,12 .H ere we explore plasmon excitations in engineered graphene microribbon arrays. We demonstrate that graphene plasmon resonances can be tuned over a broad terahertz frequency range by changing micro-ribbon width and in situ electrostatic doping. The ribbon width and carrier doping dependences of graphene plasmon frequency demonstrate power-law behaviour characteristic of two-dimensional massless Dirac electrons 4–6 . The plasmon resonances have remarkably large oscillator strengths, resulting

/pdf/graphene-plasmonics-for-tunable-terahertz-metamaterials-2qxo58e3a8.pdf

Graphene plasmonics for tunable terahertz metamaterials

Thank you for reading principles of optics electromagnetic theory of propagation interference and diffraction of light. As you may know, people have search hundreds times for their favorite novels like this principles of optics electromagnetic theory of propagation interference and diffraction of light, but end up in harmful downloads. Rather than enjoying a good book with a cup of coffee in the afternoon, instead they are facing with some infectious bugs inside their computer.

Principles Of Optics Electromagnetic Theory Of Propagation Interference And Diffraction Of Light

In the past year, fifth-generation (5G) wireless technology has seen dramatic growth, spurred on by the continuing demand for faster data communications with lower latency. At the same time, many researchers argue that 5G will be inadequate in a short time, given the explosive growth of machine connectivity, such as the Internet-of-Things (IoT). This has prompted many to question what comes after 5G. The obvious answer is sixth-generation (6G), however, the substance of 6G is still very much undefined, leaving much to the imagination in terms of real-world implementation. What is clear, however, is that the next generation will likely involve the use of terahertz frequency (0.1–10 THz) electromagnetic waves. Here, we review recent research in terahertz wireless communications and technology, focusing on three broad topic classes: the terahertz channel, terahertz devices, and space-based terahertz system considerations. In all of these, we describe the nature of the research, the specific challenges involved, and current research findings. We conclude by providing a brief perspective on the path forward.

https://www.mdpi.com/2227-7080/7/2/43/pdf

A Perspective on Terahertz Next-Generation Wireless Communications

Terahertz time-domain spectroscopy is used to study the nature and efficiency of coupling between surface plasmon polaritons and free-space terahertz radiation by metallic gratings made from brass rods and a grooved aluminum plate. Reflection and transmission mode measurements indicate very rapid coupling and decoupling with > 70% efficiency after accounting for scattering. Results indicate a good match to theoretical coupling frequencies within the accuracy of the experimental setup.

Terahertz surface plasmon polariton coupling on metallic gratings.

Silicon prisms are used to couple free-space broadband terahertz into surface plasmon polariton (SPP) modes, otherwise known as surface electromagnetic waves (SEW) or Zenneck waves, on to polished metal surfaces. We show that coupling to surface waves occurs via edge-diffraction and hump-coupling and that attenuated total reflection is not an important coupling mechanism. Coupling and decoupling to a broadband, single-cycle SPP pulse is demonstrated with an energy efficiency of approximately 3.5%. Measurements of SPPs through thin plastic films reveal a strong surface sensitivity and suggest new configurations for maximizing THz SPP utility.

Prism coupling to terahertz surface plasmon polaritons

We experimentally and numerically study the nature of coupling between laterally paired terahertz metamaterial split-ring resonators. Coupling is shown to modify the inductive–capacitive (LC) resonances resulting in either red or blue-shifting. Results indicate that tuning of the electric and magnetic coupling parameters may be accomplished not by changing the orientation or density of SRRs, but by a design modification at the unit cell level. These experiments illustrate additional degrees of freedom in tuning the electromagnetic response, which offers a path to more robust metamaterial designs.

Tailored resonator coupling for modifying the terahertz metamaterial response

A quasi-optic terahertz (THz) imaging system that utilizes optoelectronic methods for pulsed THz generation and reception and optical methods for image formation is demonstrated and theoretically explained. The system can be used to produce coherent, field amplitude, and energy density images with diffraction-limited resolution in two transverse dimensions. Simultaneous bandwidth-limited resolution is achieved in the depth dimension by means of the ranging capabilities of the system. The system is shown to accurately produce images of several objects to verify diffraction-limited imaging. Imaging power is extended by aperture synthesis to result in transverse resolution the order of a wavelength. Several individual, coherent images are recorded, each synthetically appearing to be formed by a different element of an optical phased array. The multiple images are simply superposed to create a higher-resolution image. Theoretical calculations fully describe the broadband imaging and include aberration and diffraction effects to further verify system performance. Calculated images are a good match with experimental results.

/pdf/quasi-optic-synthetic-phased-array-terahertz-imaging-3v8610pcuc.pdf

John F. O'Hara

Papers

A Perspective on Terahertz Next-Generation Wireless Communications

Terahertz surface plasmon polariton coupling on metallic gratings.

Prism coupling to terahertz surface plasmon polaritons

Tailored resonator coupling for modifying the terahertz metamaterial response

Quasi-optic synthetic phased-array terahertz imaging