Abstract
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.
Highlights
Terahertz (THz) lies between the visible and microwave and is the last electromagnetic spectrum to be explored [1,2]
THz lens [3,4,5] is a key requirement for its wide applications in high resolution THz imaging and wireless communication [6,7]
Polarization-dependent focusing, super-resolution focusing and micro-lens arrays are reported [10,11,12]. They still suffer from low polarization conversion efficiency (PCE) and static functionalities
Summary
Terahertz (THz) lies between the visible and microwave and is the last electromagnetic spectrum to be explored [1,2]. THz lens [3,4,5] is a key requirement for its wide applications in high resolution THz imaging and wireless communication [6,7] They are accomplished via controlling the phase accumulation along propagation of polished crystals or polymers. Metasurface lens, composed of subwavelength metallic or dielectric resonator arrays, can manipulate the THz wavefront in a compact manner [8,9]. By this means, polarization-dependent focusing, super-resolution focusing and micro-lens arrays are reported [10,11,12]. To realize active and efficient design is highly demanded in THz field
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