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Spiraling Light Boosts Telecom Channels

Photonics.com
Aug 2011
NEW YORK, Aug. 29, 2011 — Physicists have mapped spiraling light that could help to harness untapped data channels in optical fibers, which could increase bandwidth and ease the burden on fiber optic telecommunications networks.

“Being able to follow polarization and other changes as light travels gives you insight into the material it travels through,” said graduate student Giovanni Milione from the Institute of Ultrafast Spectroscopy and Lasers (IUSL) at The City College of New York. Polarization is key when tracking light in an optical fiber or laser because it refers to a specific direction and orientation of the light’s movement and electric field. Detecting the polarization also lets users finely tune a laser. Such control can allow a laser to burn away one layer of material while leaving the other layers it passes through intact.


The Higher Order Poincaré Sphere model developed by physicists with the Institute of Ultrafast Spectroscopy and Lasers tracks movement of complex forms of light. (Image: CCNY)

Until now, only the simplest form of light (the ground state) could be mapped and controlled, while multiple higher channels in an optical fiber, which could be occupied by more complex light, were left sitting idle.

By expanding on a Poincaré sphere, a model that has long been used to map simple light, the IUSL team mapped light by organizing the relationship between the vector beams and vortices of light. The team’s Higher Order Poincaré Sphere (HOPS) was able to map complex light moves with both spin and orbital angular momentum in the same way one pinpoints a location on Earth using latitude and longitude.

The team said that HOPS reduces what could be pages of mathematics to single equations. “The sphere facilitates understanding, showing phase vortices are on poles and vector beams are on the equator,” said Milione. “It organizes the relationship between these vortices of light.”

“This kind of organization on the higher-level Poincaré sphere could clear the path to a number of novel physics and engineering efforts such as quantum computing and optical transitions; could greatly expand the sensitivity of spectroscopy and the complexity of computer cryptography; and might further push the boundaries of what can be 'seen',” said IUSL’s Robert Alfano.

The research was published in the journal Physical Review Letters.

For more information, visit: www.ccny.cuny.edu


GLOSSARY
poincaré sphere
A reference sphere used to represent all possible states of polarization. All linear polarizations will lie on the equator and circular polarizations will correspond with the poles. Named for the French mathematician Henri Poincaré.
polarization
With respect to light radiation, the restriction of the vibrations of the magnetic or electric field vector to a single plane. In a beam of electromagnetic radiation, the polarization direction is the direction of the electric field vector (with no distinction between positive and negative as the field oscillates back and forth). The polarization vector is always in the plane at right angles to the beam direction. Near some given stationary point in space the polarization direction in the beam...
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