Active terahertz beam manipulation with photonic spin conversion based on a liquid crystal Pancharatnam–Berry metadevice

Abstract

Active terahertz (THz) beam manipulation is urgently needed for applications in wireless communication, radar detection, and remote sensing. In this work, we demonstrate a liquid crystal (LC) integrated Pancharatnam–Berry (PB) metadevice for active THz beam manipulation. Through theoretical analysis and simulation design, the geometric phase of the PB metasurface is engineered to match the tunable anisotropic phase shift of LCs under an external magnetic field, and dynamic beam deflection accompanied by spin conversion is obtained. The experimental results show that the device realizes a dynamic modulation depth of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m1"> <mml:mrow> <mml:mo form="prefix">&gt;</mml:mo> <mml:mn>94</mml:mn> <mml:mi>%</mml:mi> </mml:mrow> </mml:math> and maximum efficiency of over 50% for the different spin states. Moreover, due to the broadband operating characteristics of devices at 0.7–1.3 THz, the deflection angles are frequency dependent with a scanning range of over <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m2"> <mml:mrow> <mml:mo form="prefix">±</mml:mo> <mml:mn>20</mml:mn> <mml:mo>°</mml:mo> </mml:mrow> </mml:math> to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m3"> <mml:mrow> <mml:mo form="prefix">±</mml:mo> <mml:mn>32.5</mml:mn> <mml:mo>°</mml:mo> </mml:mrow> </mml:math> . Moreover, the two conjugate spin states are always spatially separated in different deflection directions with an isolation degree of over 10 dB. Therefore, this metadevice provides a scheme of active THz beam deflection and spin state conversion, and it also achieves both controllable wavelength division multiplexing and spin division multiplexing, which have important potential in large-capacity THz wireless communication.

Topics & Concepts