Spin-multiplexing phase-driven varifocal metalenses for multidimensional beam splitting and binary switching

Abstract

The Pancharatnam–Berry (PB) phase, subject to geometric phase, is currently utilized to implement spin-dependent optical functions. Simultaneously achieving spin-multiplexing and varifocal performances via a single-cell-designed metasurface that purely relies on PB phases has been scarcely proposed due to the quite sophisticated degrees of freedom to be taken into account. Here, by virtue of pure PB phases composed of convex and concave phases, spin-multiplexing and varifocal metalenses based on a single-cell-designed approach are developed. The unit cell consists of Ge2Sb2Se4Te1 (GSST) nanopillar pairs setting on CaF2 substrate. By adopting the specified pure PB phases, the proposed metalenses can focus the left-handed and right-handed circularly polarized (LCP and RCP) incidences into different positions. By ingenious design, the Ge2Sb2Se4Te1-based unit cell can work like a half-wave plate at two wavelength bands depending on the Ge2Sb2Se4Te1 phase states, enabling the proposed metalenses phase-driven zoom focusing. Particularly, the unique phase transition of GSST empowers the proposed schemes with binary switching focusing merit and large switching contrast ratio. The new design strategy constitutes a novel avenue in designing spin-multiplexing and varifocal optical devices, showing great potential in imaging, optical storage and optical interconnections.

Differentiated design strategies toward broadband achromatic and polarization-insensitive metalenses

“…Conventional refractive optical components, allowing precise control of the optical wavefront by relying on gradual phase accumulations as light propagates through bulky media, are generally bulky, costly, and time-consuming to manufacture with high precision, which significantly hinders their application, especially in miniaturized and highly integrated devices. In recent years, metasurfaces, consisting of subwavelength-spaced phase shifters at an interface, have emerged as a flexible platform for shaping the wavefront by tailoring the phase, amplitude, and polarization at will, enabling the realization of various ultracompact optical components, ranging from lenses, 1 – 6 holograms, 7 – 10 and carpet cloaks 11 , 12 to beam deflectors 13 – 15 Among these devices, metalenses, metasurfaces encoded with hyperbolical phase profiles, have attracted intense attention due to their great potential for future efficient portable or wearable optical devices with small footprints and light weights.…”

Wavelength-actuated varifocal and polarization-insensitive metalenses assisted by monolayer single-celled phase-change metasurfaces

“…Nevertheless, these solutions still involve external mechanical movement, low yield and could be suspect to performance degradation over time. Fortunately, another efficient strategy, active metalenses whose optical functionalities can be dynamically tailored, enables tuning of focal length via soft mechanisms including graphene [8,36], anisotropic liquid crystals (LCs) [37,38], and phase-change materials (PCMs) [39][40][41][42]. However, graphene-based varifocal metalenses are restricted to relative small zoom range due to limited graphene's Fermi level, and LCs-integrated metalenses usually exhibit polarization-sensitive varifocal performance and is difficult to obtain continuous varifocal capability.…”