Lasers built into fiber-optics

Researchers from the University of Bath in England have crossed a gas-filled fiber optic laser with ordinary fiber optics to make a Raman laser and a frequency stabilizer -- devices that provide precise control of laser beams.

The devices, which could eventually be made the size of credit cards and laser pointers, could improve telecommunications and global positioning systems. They also could provide tiny laser sources for use with fiber-optic-based phase modulators, power attenuators, and beam splitters -- the tools that steer and tune light beams.

Lasers emit strong beams of single-color light by stimulating energized atoms to emit photons. Gas is more efficient at stimulating such emission than solid materials, but it has traditionally been difficult to produce gas-filled devices that are small and easy to connect to optical fibers.

The researchers' devices use photonic crystal fibers, which contain a lengthwise pattern of holes that can be filled with gas. The fibers are compact, flexible, and can easily be integrated into existing optical fiber networks, according to the researchers.

The researchers' made the devices using sections of photonic crystal fiber filled with hydrogen or acetylene gas and spliced into ordinary optical fiber. Laser beams pass from the gas cells to the optical fiber with relatively little light lost, according to the researchers.

The researchers' prototype Raman laser converts a pump laser beam to a lower frequency, or color. This is useful because the color of a laser beam is ordinarily fixed and is determined by the material the laser is made from. The researchers' prototype frequency stabilizer precisely calibrates lasers used for telecommunications.

The gas-filled fiber devices could be used practically in two to five years, according to the researchers. The work appeared in the March 24, 2005 issue of Nature (Compact, Stable and Efficient All-Fiber Gas Cells Using Hollow-Core Photonic Crystal Fibres).