AsianScientist (Oct. 22, 2012) – Researchers have demonstrated that light in tiny integrated arrays of emitters does not propagate in straight rays, contradicting traditional concepts in physics.
Instead, its energy travels in a spiral fashion in a hollow conical beam shape. The beams therefore look very much like a vortex or cyclone, with its light rays ‘twisted’ either left-handed or right-handed. In theory, there is no limit to how twisted the light rays can be.
The research, led by scientists from the University of Bristol and Glasgow in the U.K. and the University of Sun Yat-sen and Fudan in China, has been published in the latest issue of the journal Science.
In quantum mechanics, this feature is associated with the ‘orbital angular momentum’ (OAM) of photons – photons in such beams can be thought to orbit around the beam axis, somewhat similar to the movement of planets around the Sun or electrons around a nucleus.
When such light interacts with matter, it asserts a rotational force (a torque) on the matter; therefore it can be used as so called ‘optical spanners’ in addition to ‘optical tweezers,’ which can rotate as well as trap microscopic particles or droplets.
Different degrees of twist can also be used to transmit information – single particles of light (photons) can use these different degrees of twist to represent quantum information, where a single photon can be twisting both clockwise and anti-clockwise at the same time.
Applications are also being developed in using such light for imaging and sensing purposes. For example some molecules are chiral – they look the same under normal optical microscopes until illuminated by optical vortex beams with different degrees or directions of twist.
Conventionally, the generation of such beams relied on bulk optical elements such as plates, lenses, and holograms. These are good for research but can be inconvenient for many applications, in particular where large numbers of such beams are needed at high packing density.
In contrast, the new emitters are only a few micrometers in size and thousands of times smaller than conventional elements. They are based on silicon optical waveguides and can be made using standard integrated circuit fabrication technologies.
“Our microscopic optical vortex devices are so small and compact that silicon micro-chip containing thousands of emitters could be fabricated at very low costs and in high volume,” said Siyuan Yu, Professor of Photonics Information Systems in the Photonics Research Group at the University of Bristol.
“Such integrated devices and systems could open up entirely new applications of optical vortex beams previously unattainable using bulk optics,” he added.
The article can be found at: Cai X et al. (2012) Integrated Compact Optical Vortex Beam Emitters.
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Source: University of Bristol; Photo: Miss Yue Zhang.
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