Monolithic Spiral Metalens for Ultrahigh‐Capacity and Single‐Shot Sorting of Full Angular Momentum State

Abstract

Sorting orbital angular momentum (OAM) and spin angular momentum (SAM) of photons is crucial for optical communications, optical storage, and quantum information processing, wherein complicated optical setups or bulky devices are conventionally utilized to determine the angular momentum via repetitive interference or diffractive projection measurements. Recently, advancements in compact and single‐shot OAM detection have been made via coordinate transformation metasurfaces. Nevertheless, most of these strategies require precise separation and alignment between multiple components and cannot simultaneously distinguish full angular momentum states. Besides, the single‐shot maximum identifiable OAM mode numbers are generally limited to 60 due to the tradeoff between the mode space and reduced‐cross‐talk mode interval. Here, this work puts forward and experimentally demonstrates a monolithic spiral metalens (SML) for ultrahigh‐capacity sorting full angular momentum states. The SML focus the incident vortex beam into multiple‐turn spiral ring rather than a circle ring on the focal plane according to its topological charge, with the mode order ranging from −250 to 250. Consequently, the maximum identifiable OAM mode number is up to 168 under a single‐shot measurement, which largely surpass the best results reported hitherto. The experimental results obtained in the telecom band underpin the design approach, which may find great potential in high‐capacity communication and storage applications.

Efficient Angular Separation of the Dense Orbital Angular Momentum of Light

“…Moreover, the extended angular space of the monolithic spiral has enabled ultrahigh-capacity OAM mode-division demultiplexing . Meanwhile, it was proposed to combine the quadratic phase of the angular lens with metasurface techniques to achieve simultaneous detection of OAM and spin angular momentum (SAM). , Nevertheless, unlike the conventional lens, the pure angular lens mainly results in unavoidable side lobes in the focal plane. Hence, a hybrid lens in the angular and radial domains is proposed to improve sorting performance in both free space and fiber-integrated systems .…”

“…In the focal plane, the separated OAM spots exhibit a circular intensity distribution, which is compatible with the circular configuration of the practical fibers and detectors. Moreover, the extended angular space of the monolithic spiral has enabled ultrahigh-capacity OAM mode-division demultiplexing . Meanwhile, it was proposed to combine the quadratic phase of the angular lens with metasurface techniques to achieve simultaneous detection of OAM and spin angular momentum (SAM). , Nevertheless, unlike the conventional lens, the pure angular lens mainly results in unavoidable side lobes in the focal plane.…”

Achromatic CMOS-Integrated Four-Bit Orbital Angular Momentum Mode Detector at Three Wavelengths

“…Physically, the mechanisms for the detection of single OAM mode states can be classified as diffraction, − interference, surface plasmon polaritons, and the orbital photogalvanic effect . Notably, in practical OAM multiplexing applications, various diffraction optical elements (DOEs) for mode conversion with high efficiency have been proposed for the detection of OAM mode states. − Therein, a metasurface doublet with coordinate transformation phase distributions has been integrated onto a complementary metal oxide semiconductor (CMOS) camera, dramatically improving the compactness of the OAM sorter . However, due to dispersion in diffraction, we have not yet been able to achieve concurrent detection of superposed OAM mode states with different wavelengths in this regard.…”