A new twist on tax dollars and fiberoptics

By twisting fiberoptic strands into helical shapes, researchers have created unique structures that can precisely filter, polarize, or scatter light.

Aug 1st, 2004

I'm always interested to find out what our government is doing with my money. Don't worry, I'm not going to bore you with another polemic about "billions and billions" wasted. This is a story that came across my e-mail desk, where I usually hit the "delete" key faster than I can toss mind-numbing paper press releases into the circular file. This missive emanated from the newsroom at the National Science Foundation (NSF) in Arlington, VA.

The NSF is better than most federal agencies at the public relations pitch. In fact, you might want to download these PR messages on your own. You can get these releases directly from the NSF by e-mailing to join-nsfnews@lists.nsf.gov. In the body of the message, type "subscribe nsfnews" followed by your name (ie., "subscribe nsfnews Fred Flintstone").

The story that caught my eye quickly enough to avoid the electronic oblivion of my e-mail trash was headed: "A new twist on fiber optics: spiraling glass fibers provide a new way to control the behavior of light." The release (NSF PR 04-088; July 1, 2004) concerned a tiny emerging company, Chiral Photonics (Clifton NJ), that received a mere $2 million in NSF and NIST (National Institute of Standards and Technology) grants a couple of years ago to fund some pretty nifty research by Chiral Photonics' founders, Victor Kopp, Azriel Genack, and Dan Neugroschi. It looked to me as though those pitiful millions were well spent.

By twisting fiberoptic strands into helical shapes, researchers at Chiral Photonics have created unique structures that can precisely filter, polarize, or scatter light (see Laser Focus World, January 2004, p. 13). Compatible with standard fiberoptic lines, these hair-like structures may replace bulky components in sensors, gyroscopes, and other devices. While researchers are still probing the unusual properties of the new fibers, tests show the strands impart a chiral, or "handed," character to light by polarizing photons according to certain physical properties.

In conventional optical fibers, light is transmitted from one end to the other through a round core housed within a concentric outer cladding. But, because a circular core does not develop handedness when twisted, the research team wound rectangular-core fibers to create a double helix. When the team tested the twisted fiber, they discovered that some photons left the core and entered the cladding. Photons with the same handedness as the fiber entered the cladding whereas photons with handedness opposite that of the fiber remained in the core.

With only a relatively loose twist—roughly 100 µm to form a complete turn—photons with a handedness that coincides with the fiber's twist scatter out of the core at a shallow angle and are trapped in the cladding. With a tighter twist, photons with the same handedness as the fiber scatter at a wider angle, allowing the photons to escape from the cladding into the surrounding space. Only light of a single polarization remains in the fiber. At the tightest twists, roughly one-millionth of a meter to complete a turn, photons with the same handedness as the structure are reflected backwards in the core.

Because the environment surrounding the fiber affects the wavelength of the light embedded in the cladding, "loosely" twisted fibers can serve as sensors for pressure, temperature, torque, and chemical composition. With moderately twisted fibers, researchers can manipulate the resulting polarized light in useful ways, leading to a range of applications such as gyroscopes for navigation systems, current meters for electric power stations, and chemical- and materials-analysis equipment.

Visit www.chiralphotonics.com for more information. The company is now looking to the big guys for some real money. "Chiral fiber gratings can replace fiber Bragg gratings in some applications with the possible added advantage of low-cost production," noted Winslow Sargeant, the NSF officer who oversees the Chiral Photonics SBIR Award.

Nicely done, Sarge!

Jeffrey Bairstow
Contributing Editor
jnbairstow@verizon.net

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