Narrow-angle privacy protection based on anomalous propagation characteristics at epsilon-near-zero threshold frequency of YaBa2Cu3O7 ceramic material

Abstract

In this paper, an optical privacy protection (OPP) device suitable for the TM wave by taking advantage of the anomalous propagation characteristics (APC) at epsilon-near-zero threshold frequency (ETF) of YaBa2Cu3O7 ceramic material coupled with the anti-reflection structure (AFS) is proposed. The APC at ETF can be used to provide angular transparency windows with highly selective properties in both the frequency and angle domains, while the AFS facilitates improving transmittance. Considering the limitation of temperature regulation, to control the size of the transmission window within a narrow range, prisms are introduced as the background medium. It is displayed that the proposed structure has a transmittance of more than 93 % in the region of −30°–30°, while the transmittance is close to 0 beyond −40° or 40°. The OPP covers 405–790 THz, involving the entire visible light region, and has a rectangle coefficient consistently exceeding 0.97. Taking the current process error into consideration, the thickness errors of ±5 % exert little effect on the result.