IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 37, NO. 7, JULY 2001
Chaos Shift Keying with an Optoelectronic
Encryption System Using Chaos in Wavelength
J.-B. Cuenot, L. Larger, J.-P. Goedgebuer, and William T. Rhodes
A chaos shift-keying modulation scheme in which the
transmitter and the receiver are nonlinear time-delayed feedback
systems is described. The change in the chaotic dynamics is dis-
cussed when different parameters are used to encode digital sig-
nals. The time-delay parameter is shown to assure the best condi-
tions for data recovery.
Chaos, communication system security, cryptog-
raphy, delay systems, nonlinear oscillators, optical communica-
LONG with the development of optical telecommuni-
cations systems has come an interest in secure optical
transmissions and in optoelectronics techniques for signal en-
cryption. Several optoelectronics systems have been proposed
that exploit fast chaotic dynamics as a possible alternative to
classical encryption techniques based on numerical algorithms.
The first schemes proposed relied on signal masking: a small
amplitude information signal is hidden by a large-amplitude
noise-like chaotic signal. Optical systems have been reported
theoretically ,  and experimentally from Nd : YAG lasers
, erbium-doped fiber lasers –, and semiconductor lasers
–. With such schemes, signal encoding is performed
through the continuous modulation of a dynamical variable of
a chaotic oscillator; decoding is achieved by synchronizing a
chaotic receiver to the chaotic transmitter.
A more sophisticated technique uses chaos shift-keying
(CSK), e.g., with a Chua electronic circuit, as described
by Dedieu , Parlitz , and Pinkney , or with a
Lorenz-based electronic circuit, as described by Cuomo .
Other optoelectronic-based schemes have been reported by
Celka  (using a Mach–Zehnder interferometer), by Anno-
vazzi–Lodi  (laser diode) and by Luo  (erbium-doped
fiber laser). The CSK method operates with digital information.
The method again consists of modulating one of the oscillator
parameters, thereby inducing a change in the chaotic dynamics
of the oscillator, but the modulation is now binary. An eaves-
dropper detects a pseudo-random or chaotic signal, whatever
the value of the parameter, whereas a suitably synchronized
chaos decoder can differentiate between a chaotic signal
encoding a “1” bit and a chaotic signal encoding a “0” bit. Most
Manuscript received December 18, 2000; revised March 6, 2001. This work
was supported by European Contract FET/OCCULT.
The authors are with GTL-CNRS Telecom, UMR CNRS 6603, Georgia
Tech Lorraine, 57070 Metz, France, and with the Laboratoire d’Optique P.M.
Duffieux, UMR CNRS 6603, Université de Franche-Comté, 25030 Besançon