Vassilios Yannopapas

Bio: Vassilios Yannopapas is an academic researcher from National Technical University of Athens. The author has contributed to research in topics: Metamaterial & Photonic crystal. The author has an hindex of 34, co-authored 136 publications receiving 3423 citations. Previous affiliations of Vassilios Yannopapas include University of Patras & National and Kapodistrian University of Athens.

Negative refractive index metamaterials from inherently non-magnetic materials for deep infrared to terahertz frequency ranges

Abstract: We present a new set of artificial structures which can exhibit a negative refractive index band in excess of 6% in a broad frequency range from the deep infrared to the terahertz region. The structures are composites of two different kinds of non-overlapping spheres, one made from inherently non-magnetic polaritonic and the other from a Drude-like material. The polaritonic spheres are responsible for the existence of negative effective magnetic permeability whils tt he Drude-like spheres are responsible for negative effective electric permittivity. The resulting negative refractive index structures are truly subwavelength structures with wavelength-to-structure ratio 14:1, which is almost 50% higher than has been previously achieved. Our results are explained in the context of the extended Maxwell–Garnett theory and are reproduced by calculations based on the layer Korringa–Kohn–Rostoker method, an ab initio multiple scattering theory. The role of absorption in the constituent materials is discussed. Effective medium computer F77 code is freely available at http://www.wave-scattering.com

Electromagnetically induced transparency and slow light in an array of metallic nanoparticles

Abstract: We present a classical analog of electromagnetically induced transparency occurring when light is absorbed by a two-dimensional lattice of metallic spheres mounted on an asymmetric dielectric waveguide. The transparency is manifested as a spectral hole within the surface-plasmon absorption peak of the metallic spheres and is a result of destructive interference of the waveguide modes with incident radiation. The presence of transparency windows is accompanied by slow light effect wherein the group velocity is reduced by a factor of 6000. At the same time, the minimum length for storing a bit of information is of the order of 100 nm. The proposed setup is a much easier means to achieve transparency and slow light compared to existing atomic, solid-state, and photonic systems and allows for the realization of ultracompact optical delay lines and buffers.

Plasmon-induced enhancement of quantum interference near metallic nanostructures.

Abstract: We show that the quantum interference between two spontaneous emission channels can be greatly enhanced when a three-level V-type atom is placed near plasmonic nanostructures such as metallic slabs, nanospheres, or periodic arrays of metal-coated spheres. The spontaneous emission rate is calculated by a rigorous first-principles electromagnetic Green's tensor technique. The enhancement of quantum interference is attributed to the strong dependence of the spontaneous emission rate on the orientation of an atomic dipole relative to the surface of the nanostructure at the excitation frequencies of surface plasmons.

Topological Photonics

Abstract: Topological photonics is a rapidly emerging field of research in which geometrical and topological ideas are exploited to design and control the behavior of light. Drawing inspiration from the discovery of the quantum Hall effects and topological insulators in condensed matter, recent advances have shown how to engineer analogous effects also for photons, leading to remarkable phenomena such as the robust unidirectional propagation of light, which hold great promise for applications. Thanks to the flexibility and diversity of photonics systems, this field is also opening up new opportunities to realize exotic topological models and to probe and exploit topological effects in new ways. This article reviews experimental and theoretical developments in topological photonics across a wide range of experimental platforms, including photonic crystals, waveguides, metamaterials, cavities, optomechanics, silicon photonics, and circuit QED. A discussion of how changing the dimensionality and symmetries of photonics systems has allowed for the realization of different topological phases is offered, and progress in understanding the interplay of topology with non-Hermitian effects, such as dissipation, is reviewed. As an exciting perspective, topological photonics can be combined with optical nonlinearities, leading toward new collective phenomena and novel strongly correlated states of light, such as an analog of the fractional quantum Hall effect.

Photonic crystals

Abstract: 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.

The Quantum Theory of Light

Abstract: (b) Write out the equations for the time dependence of ρ11, ρ22, ρ12 and ρ21 assuming that a light field interaction V = -μ12Ee iωt + c.c. couples only levels |1> and |2>, and that the excited levels exhibit spontaneous decay. (8 marks) (c) Under steady-state conditions, find the ratio of populations in states |2> and |3>. (3 marks) (d) Find the slowly varying amplitude ̃ ρ 12 of the polarization ρ12 = ̃ ρ 12e iωt . (6 marks) (e) In the limiting case that no decay is possible from intermediate level |3>, what is the ground state population ρ11(∞)? (2 marks) 2. (15 marks total) In a 2-level atom system subjected to a strong field, dressed states are created in the form |D1(n)> = sin θ |1,n> + cos θ |2,n-1> |D2(n)> = cos θ |1,n> sin θ |2,n-1>

On-chip natural assembly of silicon photonic bandgap crystals

Abstract: Photonic bandgap crystals can reflect light for any direction of propagation in specific wavelength ranges1,2,3. This property, which can be used to confine, manipulate and guide photons, should allow the creation of all-optical integrated circuits. To achieve this goal, conventional semiconductor nanofabrication techniques have been adapted to make photonic crystals4,5,6,7,8,9. A potentially simpler and cheaper approach for creating three-dimensional periodic structures is the natural assembly of colloidal microspheres10,11,12,13,14,15. However, this approach yields irregular, polycrystalline photonic crystals that are difficult to incorporate into a device. More importantly, it leads to many structural defects that can destroy the photonic bandgap16,17. Here we show that by assembling a thin layer of colloidal spheres on a silicon substrate, we can obtain planar, single-crystalline silicon photonic crystals that have defect densities sufficiently low that the bandgap survives. As expected from theory, we observe unity reflectance in two crystalline directions of our photonic crystals around a wavelength of 1.3 micrometres. We also show that additional fabrication steps, intentional doping and patterning, can be performed, so demonstrating the potential for specific device applications.

Past achievements and future challenges in the development of three-dimensional photonic metamaterials

Abstract: Photonic metamaterials are man-made structures composed of tailored micro- or nanostructured metallodielectric subwavelength building blocks. This deceptively simple yet powerful concept allows the realization of many new and unusual optical properties, such as magnetism at optical frequencies, negative refractive index, large positive refractive index, zero reflection through impedance matching, perfect absorption, giant circular dichroism and enhanced nonlinear optical properties. Possible applications of metamaterials include ultrahigh-resolution imaging systems, compact polarization optics and cloaking devices. This Review describes recent progress in the fabrication of three-dimensional metamaterial structures and discusses some of the remaining challenges.