October 19, 2012
Scientists Demonstrate ‘Optical Vortex Beams’ On Silicon Chip
Lee Rannals for redOrbit.com — Your Universe Online
Scientists have demonstrated integrated arrays of emitters of "optical vortex beams" onto a silicon chip for the first time.
Light in these beams, as reported to the journal Science, does not propagate in straight rays, but instead travels in a spiral fashion in a hollow conical beam shape.
The beams look like a vortex or cyclone, with its light rays "twisted" either left-handed or right-handed. The researchers wrote that there is no limit to how twisted the light rays can get.
This feature in quantum mechanics is associated with the "orbital angular momentum" of photons, which is photons in beams that can orbit around the beam axis, similar to the movement of planets around the Sun or electrons around a nucleus.
When light interacts with matter, it asserts a rotational force on the matter, which can be used as "optical spanners" in addition to "optical tweezers." Different degree of twist can also be used to transmit information.
Light beams at the same frequent with different OAM values can be used to transmit different streams of information. Single particles of light can use these different degrees of twist to represent quantum information.
Applications are also being developed to use this light for imaging and sensing purposes. For example, some molecules look the same under normal optical microscopes until they are illuminated by optical vortex beams with different degrees or directions of twist.
These beams rely on bulk optical elements like plants, lenses, and holograms, and are good for research, but can be inconvenient for applications where large numbers of these beams are needed at high packing density.
The new emitters are only a few micrometers in size and thousands of times smaller than conventional elements. They are also 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," Siyuan Yu, Professor of Photonics Information Systems in the Photonics Research Group at the University of Bristol, said in a statement. “Such integrated devices and systems could open up entirely new applications of optical vortex beams previously unattainable using bulk optics.”
The devices are readily interconnected with each other to form complex and large arrays in photonics integrated circuits. They could be used for applications like communications, sensing and microscopic particle manipulation.
"Perhaps one of the most exciting applications is the control of twisted light at the single photon level, enabling us to exploit the quantum mechanical properties of optical vortices for future applications in quantum communications and quantum computation," Dr Mark Thompson, Deputy Director of the Centre for Quantum Photonics at the University of Bristol, said in a statement.