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Nanochip Captures the Power of Twisted Light

An Australian research team has designed a nanophotonic chip that can achieve unparalleled levels of control over the angular momentum of light. The work, published in Science (http://tinyurl.com/hqzoqb3), opens new opportunities to use angular momentum for the generation, transmission, processing and recording of information, and could also be used to help scientists better understand the evolution and nature of black holes.

While travelling approximately in a straight line, a beam of light also spins and twists around its optical axis. The angular momentum of light measures the amount of this dynamic rotation, and could be harnessed to improve the capacity of optical fibres by creating parallel light channels – an approach known as “multiplexing”.

However, the creation of angular momentum multiplexing on a chip has remained a major challenge as there is no material in nature capable of sensing twisted light.

“By designing a series of elaborate nano-apertures and nanogrooves on the photonic chip, our team has enabled the on-chip manipulation of twisted light for the first time,” said Prof Min Gu of RMIT University. “The design removes the need for any other bulky interference-based optics to detect the angular momentum signals.

“Our discovery could open up truly compact on-chip angular momentum applications such as ultra-high definition displays, ultra-high capacity optical communications and ultra-secure optical encryption. It could also be extended to characterise the angular momentum properties of gravitational waves to help us gain more information on how black holes interact with each other in the universe.”

The team devised nanogrooves to couple angular momentum-carrying beams into different plasmonic angular momentum fields, with the nano-apertures subsequently sorting and transmitting the different plasmonic angular momentum signals. “Our specially designed nanophotonic chip can precisely guide angular momentum data signals so they are transmitted from different mode-sorting nano-ring slits without losing any information,” said Haoran Ren, a PhD candidate at Swinburne University of Technology.

Gu added that the research offers a precise method of studying black holes as it enabled full control over twisted light, including both spin angular momentum and orbital angular (Oangular) momentum. “Due to the fact that rotating black holes can impart Oangular momentum associated with gravitational waves, an unambiguous measuring of the Oangular momentum through the sky could lead to a more profound understanding of the evolution and nature of black holes in the universe,” he said.