Abstract-Tunable perfect magnetic mirrors and retroreflectors in terahertz band

Hao Song, Lei Sun, and Guo Ping Wang

The reflectivity (blue curve) and the phase change (red dashed curve) of the reflected wave from a reflective metasurface to the normal incident TE electromagnetic wave. (b) The electric field distribution of an incident wave in one period of the metasurface at 0.286 THz (point A). (c)-(e) The electric field Ez${\mathrm{E}}_{\mathrm{z}}$ distribution, 𝑧$z$-component of the current density (Jz${\mathrm{J}}_{\mathrm{z}}$, A/m3$\mathrm{A}/{\mathrm{m}}^3$), and electromagnetic power loss density (Qe${\mathrm{Q}}_{\mathrm{e}}$, W/m3$\mathrm{W}/{\mathrm{m}}^3$) of the dip indicated in (a), respectively. (f) The reflectivity (blue curve) and the phase change (red dashed curve) of the reflected wave at 0.286 THz versus the angle of incidence from 0∘$0^{\circ }$ to 15.5∘$1{5.5}^{\circ }$. The inset exhibits the electric field distribution of wave in one period of the metasurface at the angle of incidence of 5.7∘$5{.7}^{\circ }$. (g) The reflectivity (blue solid curve, R0${\mathrm{R}}_0$), the transmissivity (blue dashed curve, T0${\mathrm{T}}_0$), and the phase change (red curve, △𝜙$△\varphi$) of the reflected wave from periodic micro cylindrical rod array to the normal incident TE electromagnetic wave. (h)-(i) The energy density distribution of a normal incident Gaussian beam at 0.286 THz with an amplitude of 1 V/m in the metasurface and periodic micro cylindrical rod array (without substrate), respectively. The incident wave marked by a red arrow, the reflected wave marked by a blue arrow and R0${\mathrm{R}}_0$, the transmission wave marked by a white arrow and T0${\mathrm{T}}_0$.

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-28-1-753

A magnetic mirror operating in the terahertz band is designed based on the functional reflective metasurface, which is simply constructed by a one-dimensional periodic lithium tantalate micro cylindrical rod array on a Teflon substrate coated with a metal layer at the bottom and reflects the incoming electric field with a zero-phase change. Magnetic dipole resonance of the micro cylindrical rods excited in the metasurface is attributed to the perfect magnetic mirror at the frequency of 0.286 THz with the reflectivity of R = 0.98 for a normal incident electromagnetic wave. By real-time varying the direction from normal (0) to 28.45 degrees and the frequency from 0.286 to 0.382 THz of the incident wave, the metasurface can still behave as a perfect magnetic mirror with the reflectivity as high as 0.99. Most interestingly, in this case, the metasurface possesses the property of a retroreflector that the reflected wave returns along the direction of the incident wave, which is consistent with the grating equation. The tunable perfect magnetic mirror effect and the retroreflector property may provide ways in novel photonic devices and sensing applications.

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