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MICROSTRUCTURED FIBERS
Use of Microstructured
Fibers in Optical Amplifiers,
Wavelength Shifters and
All-Optical Switches
Jay. E. Sharping, Marco Fiorentino, Prem Kumar and
Robert. S.Windeler
ngoing advances in the fabrication
and characterization of microstructure fibers (MFs)—which are also known
as photonic-crystal fibers or holey fibers—
have allowed researchers over the past year
to propose and demonstrate a number of
viable photonic applications using this
material.1-4 Microstructure
fibers that exhibit singlemode behavior over a wide
wavelength range can be
fabricated with a relatively
small core area, allowing
one to take greater advantage of the weak (3) nonlinearity of glass. By doing
so, one reduces the pump
power and fiber length requirements, the principal
drawbacks of previously
demonstrated fiber-based
nonlinear optic devices.
Furthermore, because the
MF design parameters permit greater control over the
dispersion properties of
the fiber, MFs can be designed to favor certain
pulse-propagation effects
or nonlinear interactions.
In particular, we have explored the potential for using MFs for broadband optical amplification, wavelength shifting and all-optical switching. Our experiments demonstrate the feasibility of using MFs to
perform essential functions in high-speed all-optical processing.
Broadband optical amplification and
wavelength shifting can be achieved
through nondegenerate four-wave mixing
where approximate phase matching is
achieved by injecting strong pump pulses
at a wavelength slightly longer than the
zero-dispersion wavelength of the MF. The
small amount of intrinsic phase mismatch
is offset by the phase shift on the pump induced by self-phase modulation. The result is that, in the presence of a strong
pump beam, a weak signal beam is ampli-
O
Figure 1. (a) Signal output average power vs.
pump peak power, showing the threshold behavior
of a MF-based OPO. Inset: a typical intracavity
optical spectrum. (b) Optical spectra showing the
increase in the switched signal power as the pump
peak power increases. Inset: relative power measured in each port of the switch vs. the pump peak
power.
28 Optics & Photonics News
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December 2002
fied, and an idler (conjugate) beam is generated at a wavelength dictated by energy
conservation [see the inset in Fig. 1(a)].
Using only 6.1 m of MF, we built an amplifier that achieved single-pass gains of over
13 dB.1 We also constructed an opticalparametric oscillator (OPO) in which the
signal is resonated by use of an optical cavity; in this case we achieved a pump-tosignal power conversion efficiency of 4%
[see Fig. 1(a)].4
All-optical switching can be achieved
via cross-phase modulation between
strong pump and weak signal pulses. In
this case, phase matching is not necessary
and no energy is coupled between the
pump and the signal, but there is a pumppower-dependent induced phase shift on
the signal. By placing this phase shifting
mechanism in one arm of an interferometer, the induced phase shift can be converted to amplitude changes at the two ports
of the interferometer. Experiments using
pump and signal wavelengths near
1540 nm [see Fig. 1(b)] show the expected
switching behavior.2 Using 5.8 m of MF,
one can achieve a phase shift for a pump
peak power of about 9.5 W. Similar measurements (not shown) were made for
pump and signal wavelengths near 780 nm
in order to minimize the effects of groupvelocity mismatch, which is nearly zero for
this fiber at this wavelength. We achieved
complete switching, i.e., a full phase
shift, using only 3 W of pump peak power.
Acknowledgments
This research was supported in part by the
U.S. Army Research Office under a collaborative MURI grant (DAAD19-00-1-0177)
and the associated MURI Fellowship
(DAAD19-00-1-0469) for J. E. Sharping.
References
1.
2.
3.
4.
J. E. Sharping, M. Fiorentino,A. Coker, P. Kumar and
R. S.Windeler, Opt. Lett. 26, 1048, (2001).
J. E. Sharping, M. Fiorentino, P. Kumar and R. S.
Windeler, Photon.Technol. Lett. 14, 77 (2002).
Z.Yusoff, J. H. Lee,W. Belardi,T. M. Monro, P. C.Teh
and D. J. Richardson, Opt. Lett. 27, 424, (2002).
J. E. Sharping, M. Fiorentino, P. Kumar and R. S.
Windeler, to appear in Opt. Lett. 27, Sept., (2002).
Jay. E. Sharping ([email protected]), Marco Fiorentino and Prem Kumar are with the Center
for Photonic Communication and Computing, Department of Electrical and Computer Engineering,
Northwestern University. Robert. S. Windeler is with
OFS Laboratories, Murray Hill, New Jersey.