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
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).
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