Abstract-Thermally sensitive scattering of terahertz waves by coated cylinders for tunable invisibility and masking

Andriy E. Serebryannikov, Kamil B. Alici, Ekmel Ozbay, and Akhlesh Lakhtakia

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-1-1

Temperature-sensitive scattering of terahertz (THz) waves by infinitely long, cylindrical core-shell structures was theoretically studied. Each structure is a dielectric cylinder coated with an InSb shell illuminated by either a transverse-electric (TE) or a transverse-magnetic (TM) plane wave. InSb is a thermally tunable semiconductor showing a transition from dielectric to plasmonic state at THz frequencies. Accordingly, the total scattering efficiency (TSE) can be thermally tuned for both polarization states of the incident plane wave. The spectral locations of the maxima and minima of the TSE of an InSb-coated cylinder can be exploited for cloaking the core. At least three scenarios lead to the strong suppression of scattering by a single core-shell structure in different spectral regimes when the temperature is fixed. The excitation of localized surface-plasmon resonances is the feature being common for two of them, while the effect of volumetric resonance dominates in the third scenario. Regimes that are either highly or weakly sensitive to the core material were identified. Weak sensitivity enables masking, i.e., the core material cannot be identified by a far-zone observer. The TSE minima are usually significantly sensitive to the polarization state, but ones with weak sensitivity to the polarization state also exist.

© 2018 Optical Society of America

Abstract-Single and cascaded, magnetically controllable metasurfaces as terahertz filters

Andriy E. Serebryannikov, Akhlesh Lakhtakia, and Ekmel Ozbay
https://www.osapublishing.org/josab/abstract.cfm?uri=josab-33-5-834

Transmission of a normally incident, linearly polarized, plane wave through either a single electrically thin metasurface comprising H-shaped subwavelength resonating elements made of magnetostatically controllable InAs or a cascade of several such metasurfaces was simulated in the terahertz regime. Stop bands that are either weakly or strongly controllable can be exhibited by a single metasurface by proper choice of the orientation of the magnetostatic field, and a ∼19% downshift of stop bands in the 0.1–5.5 THz spectral regime is possible on increasing the magnetostatic field strength from 0 to 1 T. Better controllability and wider bandwidths are possible by increasing the number of metasurfaces in a cascade, although increase of the total losses can lead to some restrictions. ON/OFF switching regimes, realizable either by applying/removing the magnetostatic field or just by changing its orientation, exist.

© 2016 Optical Society of America

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Abstract-One-way absorption of terahertz waves in rod-type and multilayer structures containing polar dielectrics

Andriy E. Serebryannikov, Shunji Nojima, and Ekmel Ozbay

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.90.235126

One-way absorption can be obtained at terahertz frequencies in low-profile rod-type and multilayer dielectric structures with broken spatial inversion symmetry, which contain either a rod layer or an ultrathin homogeneous layer made of a polar dielectric. Perfect absorption for one of the two opposite incidence directions and perfect reflection for the other one are observed at the edge of the polaritonic gap in a wide range of the incident angle variation, when the thickness of the entire structure is of the order of the incident wavelength. Moreover, this regime appears in a wide frequency range, in which the forward-to-backward absorption contrast is strong. The exploited mechanism is connected with the parameter adjustment that enables the location of the polaritonic gap of the polar dielectric, of which the lossy part of the structure is made, inside the stop band arising due to the periodicity of the lossless part of the structure that is made of a nondispersive dielectric. It also exploits absorption enhancement in the lossy part by backing it with the highly reflecting lossless part, which has alternating stop and pass bands.

DOI: http://dx.doi.org/10.1103/PhysRevB.90.235126

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• Published 16 December 2014
• Received 14 May 2014
• Revised 26 November 2014

©2014 American Physical Society

Abstract-Asymmetric transmission of terahertz waves using polar dielectrics

Andriy E. Serebryannikov, Ekmel Ozbay, and Shunji Nojima  »View Author Affiliations

Optics Express, Vol. 22, Issue 3, pp. 3075-3088 (2014)

Asymmetric wave transmission is a Lorentz reciprocal phenomenon, which can appear in the structures with broken symmetry. It may enable high forward-to-backward transmittance contrast, while transmission for one of the two opposite incidence directions is blocked. In this paper, it is demonstrated that ultrawideband, high-contrast asymmetric wave transmission can be obtained at terahertz frequencies in the topologically simple, i.e., one- or two-layer nonsymmetric gratings, which are entirely or partially made of a polar dielectric working in the ultralow-ε regime inspired by phonon-photon coupling. A variety of polar dielectrics with different characteristics can be used that gives one a big freedom concerning design. Simple criteria for estimating possible usefulness of a certain polar dielectric are suggested. Contrasts exceeding 80dB can be easily achieved without a special parameter adjustment. Stacking a high-ε corrugated layer with a noncorrugated layer made of a polar dielectric, one can enhance transmission in the unidirectional regime. At large and intermediate angles of incidence, a better performance can be obtained owing to the common effect of nonsymmetric diffractions and directional selectivity, which is connected with the dispersion of the ultralow-ε material. At normal incidence, strong asymmetry in transmission may occur in the studied structures as a purely diffraction effect.

© 2014 Optical Society of America