Abstract
Temperature-mediated appearance and disappearance of a deflection grating in a diffracting structure is possible by employing InSb as the grating material. InSb transits from the dielectric state to the plasmonic state in the terahertz regime as the temperature increases, this transition being reversible. An intermediate state is the vacuum state in which the real part of the relative permittivity of InSb equals unity while the imaginary part is much smaller. Then the grating virtually disappears, deflection being impossible as only specular reflection can occur. This ON/OFF switching of deflection and relevant angular filtering are realizable over wide ranges of frequency and incidence angle by a temperature change of as low as 20 K. The vacuum state of InSb invoked for ON/OFF switching of deflection and relevant angular filtering can also be obtained for thermally tunable materials other than InSb as well as by using non-thermal mechanisms.
Highlights
Terahertz, mid-infrared, and near-infrared devices that are tunable in real time have been attracting considerable attention for about a decade
We introduce the vacuum state as an intermediate state to enable and control wideband and wide-angle deflection by a diffraction grating
For the purpose of demonstration, we restrict our theoretical consideration to the effect of nearly perfect deflection in the reflection mode, in very wide ranges of the frequency and the incidence angle[17,18], these ranges being wider than those realizable from most of other known approaches to angular filtering[19,20,21]
Summary
Mid-infrared, and near-infrared devices that are tunable in real time have been attracting considerable attention for about a decade. A dramatic change in the electromagnetic state of a material is strictly unnecessary for dynamic tunability[1,4,7], the transition of a material from/to the dielectric state to/from the plasmonic state affords exciting possibilities in various tuning scenarios. The epsilon-near-zero state (relative permittivity = 0), an intermediate state between the plasmonic and dielectric ones, has garnered attention as well[2,13,14,15,16]. We introduce the vacuum state (relative permittivity = 1) as an intermediate state to enable and control wideband and wide-angle deflection by a diffraction grating. We note that the materials in which the vacuum state is exhibited as a result of the plasmonic-to-dielectric state transition, exhibit an epsilon-near-zero intermediate state. An epsilon-near-zero grating can be manifested in our structure, albeit at another temperature; that issue lies beyond the scope of this paper
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