Random Distributed Feedback
Sergei K. Turitsyn, Sergey A. Babin, Atalla E. El-Taher, Paul Harper, Dmitriy V. Churkin,
Sergey I. Kablukov, Juan Diego Ania-Castañón, Vassilis Karalekas and Evgenii V. Podivilov
Abasic laser scheme normally requires two key elements: A gain material
that provides amplification and an optical cavity that traps the light, creating
positive feedback. Lasing occurs when the
total gain in the cavity overcomes the total cavity loss. Operational characteristics
of conventional lasers are determined
both by the distinctive features of the
gain medium and by the cavity design
that defines the structure of laser modes.
In random lasers with no cavity (or
with an open cavity), 1, 2 the output characteristics are determined by the build-up of radiation due to multiple scattering in the gain medium, resulting in
randomly embedded local spatial modes
that may coexist with non-localized
extended modes. 3 Random lasers have
advantages, such as simple technology
that does not require a precise microcavity, and low production cost. However,
the properties of their output radiation
are rather special in comparison to those
of conventional lasers, and they are usually characterized by complex features in
the spatial, spectral and time domains.
We demonstrated a new type of
one-dimensional laser with random
distributed feedback based on Rayleigh
scattering (RS), which is present in any
transparent glass medium due to natural
inhomogeneities of refractive index. 4 ;e
cylindrical fiber waveguide geometry
provides transverse confinement, while
the cavity is open in the longitudinal direction and does not include any regular
;ough Rayleigh backscattering is
extremely weak, the e;ect may be accumulated and amplified in the long fiber.
Using stimulated Raman scattering to
provide distributed amplification, we
demonstrate random lasing in low-cost,
open-cavity standard transmission fiber
with stationary narrowband output
power of about 300 m W from two fiber
Random distributed feedback
Lost scattered photons
2 pump lasers
Principle of random distributed feedback ;ber laser operation. Photons propagating
in a long ;ber are coherently scattered in a 83-km ;ber by random refractive-index
inhomogeneities complying with Rayleigh’s law. Most of the scattered photons leak
out of the ;ber core. Only Q 10-3 of them are backscattered and guided by the ;ber.
Two pump waves coupled at z=0 provide distributed Raman gain along the ;ber. The
backscattered guided photons can be ampli;ed if total gain is larger than the loss level,
which is ful;lled for all points |z|<LRS. As a result, two forward and backward propagat-
ing waves are generated. The numerically calculated laser power distribution (red) and
Raman gain (blue) are shown.
ends. ;e weakness of the RS-based
random distributed feedback makes the
operation and properties of the demonstrated lasers profoundly di;erent from
those of both traditional random lasers
and conventional fiber lasers.
Note that RS might also have a critical impact on performances of conventional (with point reflectors) fiber lasers
with a long cavity. In particular, the
mode structure of Raman fiber lasers
with linear cavity formed by highly
reflecting mirrors/gratings is washed out
at a resonator length of about 300 km. 5
In conclusion, the lasing provided by
weak random distributed feedback in
an amplifying fiber waveguide medium
constitutes a new class of laser—the ran-
dom distributed feedback fiber laser. We
believe that new fundamental science as
well as new applications and technolo-
gies, in particular, for telecommunica-
tions and sensing, will emerge as a result
of our development. t
Sergei K. Turitsyn ( firstname.lastname@example.org), Atalla
E. El-Taher, Paul Harper, Juan Diego Ania-Castañón,
and Vassilis Karalekas are with the Photonics Research Group, Aston University, Birmingham, United
Kingdom. Ania-Castañón is also with the Instituto
de Óptica, CSIC, in Madrid, Spain. Sergey A. Babin,
Dmitriy V. Churkin, Sergey I. Kablukoy and Evgenii
V. Podivilov are with the Institute of Automation and
Electrometry, SB RAS, Novosibirsk, Russia.
1. H. Cao. J. Phys. A: Math. Gen. 38, 10497–535 (2005).
2. D.S. Wiersma. Nature Physics 4, 359-67 (2008).
3. J. Fallert et al. Nature Photonics 3, 279–82 (2009).
4. S.K. Turitsyn et al. Nature Photonics, 4, 231-5 (2010).
5. S.K. Turitsyn et al. Phys. Rev. Lett. 103, 133901 (2009).