Zeno Switching Through Inverse Raman
Scattering in Optical Fiber
K. Kieu, L. Schneebeli, R.A. Norwood and N. Peyghambarian
All-optical switching is an alternative to electrical switching for optoelectronic systems in information processing and communication. ;e much
faster operating speed makes all-optical
switching desirable as long as absorptive
losses are negligible. In general, an optical switch involves three components:
the signal beam, the control beam and
the medium through which the switching operation is carried out.
Zeno switching refers to switching
of a signal optical beam in the presence of a control-pump beam in which
neither beam is separately absorbed
(or interacts with the medium). 1 To
date, realization of a Zeno switch has
been challenging since there should be
no absorption in the o; state. Various
all-optical switching schemes have been
using photonic-crystal cavities in which
a pump beam induces a resonance shift
of the cavity mode and hence control
of the signal beam. 2, 3 In a related
approach, researchers have applied a
silicon planar ring resonator to enhance
the refractive-index dependence on the
exciting pump pulse intensity. 4
While these strategies exhibit a low
switching energy at a short time scale,
true absorption is involved because
carriers are generated, contrary to the
Zeno-switch concept. Here we present
evidence for demonstration of Zeno
switching using inverse Raman scattering (IRS) in an optical fiber. Light at the
anti-Stokes frequency is strongly attenuated in the presence of a pump field.
;e switching contrast that is determined by the observed level of induced
absorption via IRS in the optical fiber is
more than 20 dB in a time scale of less
than 5 ps. We extracted the full Raman
response function experimentally and
found excellent agreement between
theory and experiment.
0.01 m W
10 m W
25 m W
40 m W
50 m W
Measured (a) and calculated (b) IRS spectra in high NA germanium-doped optical ;ber.
The black vertical line shows the cutoff wavelength of the WDM ;lter, which is around
1,510 nm. When the pump power is increased, the spectral components of the signal
beam that matched the Raman vibration frequencies of the material suffer signi;cant loss.
This appears as a dip in the optical spectrum of the anti-Stokes signal beam.
A mode-locked fiber oscillator operating near 1,560 nm is amplified in an
Er-doped fiber amplifier. Eighty percent
of the power after the amplifier is used
to generate a broad supercontinuum,
which is then used as the anti-Stokes
probe beam. ;e other 20 percent is
passed through a narrow (about 1. 5 nm
FWHM) band-pass filter working
around 1,560 nm to generate narrow
bandwidth pump pulses. ;e pump and
the anti-Stokes pulses (both about 3 ps)
are combined into a short segment of
an optical fiber under test. ;e average
power of the probe beam is about 5 m W
while the pump power is roughly 50 m W
with a repetition rate of 50 MHz.
Typical measured IRS spectra of a
small core, 2-m, high-NA optical fiber
are shown in (a). ;e probe beam experiences significant loss at the anti-Stokes
line as the pump power is increased with
about 22 dB contrast at 50 m W pump
average power. We performed numerical simulations of IRS in optical fiber
using coupled nonlinear Schrödinger
equations for the anti-Stokes and pump
pulses propagating through an optical
fiber. ;e calculated result shown in (b)
is in very good agreement with the measured data in (a).
In conclusion, we have observed Zeno
switching through IRS in an optical fiber.
IRS is a good candidate to build a Zeno-type all-optical switch. We achieved
stimulated loss of more than 20 dB in
2 m of highly GeO2-doped optical fiber.
Compared to silicon waveguides, IRS
in optical fiber does not su;er from additional loss due to two-photon induced
absorption. In addition, our technique is
compatible with current optical communication networks that are largely based
on optical fibers. t
;e authors acknowledge helpful discussions
with Joseph Perry of the Georgia Institute
of Technology. ;is work is supported by
the DARPA ZOE program (Grant No.
W31P4Q-09-1-0012) and the CIAN ERC
(Grant No. EEC-0812072).
K. Kieu, L. Schneebeli, R.A. Norwood and N.
Peyghambarian ( firstname.lastname@example.org) are with the
College of Optical Sciences, University of Arizona,
Tucson, Ariz., U.S.A.
1. L. Schneebeli et al. Phys. Rev. A 81, 053852 (2010).
2. K. Nozaki et al. Nature Photon. 4, 477 (2010).
3. T. Tanabe et al. Appl. Phys. Lett. 87, 151112 (2005).
4. V.R. Almeida et al. Nature 431, 1081 (2004).