Spiniform phase-encoded metagratings entangling arbitrary rational-order orbital angular momentum

• Published in: Light, science & applications Vol. 7; no. 3; p. 17156
• Main Authors: Huang, Kun, Liu, Hong, Restuccia, Sara, Mehmood, Muhammad Q, Mei, Sheng-Tao, Giovannini, Daniel, Danner, Aaron, Padgett, Miles J, Teng, Jing-Hua, Qiu, Cheng-Wei
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 09-03-2018; Springer Nature B.V; Nature Publishing Group
• Subjects: 639/624/400/482; 639/766/1130/2799; 639/766/400/1021; Applied and Technical Physics; Atomic; Classical and Continuum Physics; Information science; Lasers; Light; Microparticles; Molecular; Optical and Plasma Physics; Optical Devices; Optics; original-article; Photonics; Physics; Physics and Astronomy; Quantum theory; nanophotonics; orbital angular momentum; metasurface; superposition state
• ISSN: 2047-7538; 2095-5545; 2047-7538
• DOI: 10.1038/lsa.2017.156

Quantum entanglements between integer-order and fractional-order orbital angular momentums (OAMs) have been previously discussed. However, the entangled nature of arbitrary rational-order OAM has long been considered a myth due to the absence of an effective strategy for generating arbitrary rational-order OAM beams. Therefore, we report a single metadevice comprising a bilaterally symmetric grating with an aperture, creating optical beams with dynamically controllable OAM values that are continuously varying over a rational range. Due to its encoded spiniform phase, this novel metagrating enables the production of an average OAM that can be increased without a theoretical limit by embracing distributed singularities, which differs significantly from the classic method of stacking phase singularities using fork gratings. This new method makes it possible to probe the unexplored niche of quantum entanglement between arbitrarily defined OAMs in light, which could lead to the complex manipulation of microparticles, high-dimensional quantum entanglement and optical communication. We show that quantum coincidence based on rational-order OAM-superposition states could give rise to low cross-talks between two different states that have no significant overlap in their spiral spectra. Additionally, future applications in quantum communication and optical micromanipulation may be found.
Orbital angular momentum: device generates beams with variable angular momentum
A device that can generate light beams with continuously variable values of orbital angular momentum (OAM) has been demonstrated. Quantum entanglement between photons with integer or fractional OAM has been realized, but until now it has been difficult to generate light beams that have an arbitrary rational amount of OAM. Now, Cheng-Wei Qiu of the National University of Singapore and co-workers have designed and tested an analog vortex transmitter of rational-order OAM, that consists of two tilted gratings under a circular aperture. Plane waves of green light incident on the aperture are converted into vortex beams with a continuously controllable amount of OAM that is determined by the effective variation in size of the aperture across the device. Potential applications for the device include selection and sorting of microparticles, spiral imaging and high-dimensional quantum entanglement.