Lynn Savage, email@example.com
VILLENEUVE D’ASCQ, France – Optical parametric amplification is a common method for improving laser-based telecommunications
by boosting signal strength across long lengths of fiber optics. If you chirp the
signal pulses – stretching and recompressing each pulse – you get amplified
broadband pulses that have high gain, increased conversion efficiency and several
other benefits. What you don’t have, however, is a simple system, because
the technique, dubbed optical parametric chirped pulse amplification, requires the
incorporation of bulky nonlinear crystals several millimeters long that further
demand careful alignment at all times.
A schematic shows the experimental setup of a fiber-based optical
parametric chirped pulse amplifier. FOPA = fiber optical parametric amplifier; RF
= radio frequency; TL = tunable laser; PM = phase modulator; EDFA = erbium-doped
fiber amplifier; PC = polarization controller; HNLF = highly nonlinear fiber; CFBG
= chirped fiber Bragg grating; PBS = polarization beamsplitter. Reused with permission
of the Optical Society of America.
Now, researchers led by Arnaud Mussot of Université de Lille
1 have streamlined the amplification process by making it an all-fiber system. The
results are promising not only for improving telecommunications systems but also,
perhaps, for advancing studies of the interactions between laser light and matter.
Fiber-based optical parametric chirped pulse amplification systems
were proposed several years ago, but, according to Mussot, the original group did
not have the ability at the time to develop the photonic crystal fiber needed to
replace the nonlinear crystal typically used to create chirp. His group, however,
Mussot and his colleagues at Université de Mons in Belgium,
at Commissariat à l’Energie Atomique (CEA) in Le Bop and at the University
of Alcalá in Alcalá de Henares, Spain, integrated a linearly chirped
fiber Bragg grating into a fiber optical parametric amplifier. They created pulses
using a tunable continuous-wave laser as a seed source and a microwave source to
modulate the beam.
The 15-cm-long chirped fiber Bragg grating stretched the picosecond-scale
pulses of 1550-nm light by 24.6 dB and then compressed the pulses to their initial
length without significant distortion.
The group reported its technique in the June 1, 2010, issue of
According to Mussot, the team currently is adapting the technique
to work with femtosecond-scale pulses at about 1 µm, which would be useful for laser-matter
experiments. Working in this wavelength range requires the development of novel
photonic crystal fibers and the use of an Yb-doped mode-locked fiber laser as the
seed signal. If successful, the gain in such a system is expected to be greater
than 60 dB.
The technique’s potential is not all that excites Mussot,
however. The collaborative effort between his university and CEA is paying major
“It was a strong collaboration between these two institutes,
[and it] is still running,” he said.