Twisted fiber filters light

Researchers from the City University of New York, Queens and Chiral Photonics, Inc. have devised a way to control light inside optical fiber communications lines.

The method involves putting periodic twists in fiber to select the polarization of light that is transmitted through the fiber. The electric field of an unpolarized light pulse or beam is oriented on a plane perpendicular to the pulse or beam. When light is polarized its electric field is narrowed to one direction within the plane or rotates around the plane.

Telecommunications networks, navigation system gyroscopes, and optical current sensors that monitor electric power stations all depend on polarized light.

The method could enable faster data transmission rates in fiber-optic lines and new twists on devices like lasers and sensors.

The researchers made their prototype chiral fibers using a relatively simple process: heating the optical fiber, then quickly and precisely twisting the fibers so that the fiber core forms a double helical structure much like DNA. The effect of the structure on light depends on how tightly the fiber is twisted.

A loose twist allows the device to act as a sensor, a moderate twist acts as a polarizer, and a tight twist acts as a filter or laser. The researchers' prototype devices include pressure, temperature and fuel sensors.

The researchers have produced a practical in-fiber light polarizer, and plan to produce a chiral fiber laser within 18 months, according to the researchers. The work appeared in the July 2, 2004 issue of Science.