Abstract-Liquid crystal tunable terahertz lens with spin-selected focusing property

Zhixiong Shen, Shenghang Zhou, Shijun Ge, Wei Duan, Lingling Ma, Yanqing Lu, and Wei Hu

Fig. 1 (a) The schematic illustration of the spin-selected lens. (b) The photo of the sample under crossed polarizers (indicated by two yellow arrows). Scale bar: 1 mm. (c) The designed phase diagram. Inset shows a magnified 6 × 6 pixel array, which is divided into lattice I and II. The lattice periodicity p is 152 μm. (d) The focusing functions of lattice I and II.

We propose and demonstrate an active spin-selected lens with liquid crystal (LC) in the terahertz (THz) range. The lens is a superposition of two geometric phase lenses with separate centers and conjugated phase profiles. Its digitalized multidirectional LC orientations are realized via a dynamic micro-lithography-based photo-patterning technique and sandwiched by two graphene-electrode-covered silica substrates. The specific lens can separate the focusing spots of incident light with opposite circular polarizations. Its focusing performance from 0.8 to 1.2 THz is characterized using a scanning near-field THz microscope system. The polarization conversion efficiency varies from 32.1% to 70.2% in this band. The spin-selected focusing functions match well with numerical simulations. Such lens exhibits the merit of dynamic functions, low insertion loss and broadband applicability. It may inspire various practical THz apparatuses.

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