JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 31, NO. 3, FEBRUARY 1, 2013 461
Simulation of Bidirectional Long-Distance Chaos
Communication Performance in a Novel Fiber-Optic
Chaos Synchronization System
Jia-Gui Wu, Zheng-Mao Wu, Yu-Ran Liu, Li Fan, Xi Tang, and Guang-Qiong Xia
Abstract—A novel fiber-optic chaos synchronization system
allo
wing bidirectional long-distance chaos communication is
proposed. For this system, chaos synchronization between two
response lasers (RLs) is achieved via an identical d riven chaotic
si
gnal injection from a remote driving laser (DL) over a long-dis-
tance fiber. The simulated results show that under suitable
operation conditions, high-quality chaos synchronization between
the two RLs can be obtained while the synchronization quality
between any one of RLs and the DL is bad, which is useful for
improving the system security. Using the two synchronized chaos
output signals from RLs as two chaotic carriers and adopting a
novel message encryption and decryption method, the communi-
cation performances, the impact of long-distance fiber channel
and the security of this system, have been analyzed. After adopting
an optimized system configuration, two 10 Gb/s messages p ropa-
gating along opposite direction can be effectively decrypted over
100 km fiber channel.
Index Terms—Chaos, chaos communication, optical fiber, semi-
conductor lasers, synchronization.
I. INTRODU CTION
C
HAOS synchronization, presented by Pecora and Carroll
in 1
990 [1], gives the possibility to app ly in informa-
tion secure field at a physical layer. In past years, many ef-
forts h ave been dedicated to the topic of chaos synchroniza-
ti
on and communication based on semiconductor lasers (SLs)
[2]–[26] due t o their fast response and inherent compatibility
with fiber optic networks. In 2005, Argyris et al. successfully
de
monstrated chaos-based 1 Gb/s message unidirectional com-
munication over 120 km via a com m ercial fiber-optic network
[7]. Recently, Lavrov et al. reported that a 10 Gb/s message,
hi
dden in the ph ase of optical chaos, is unidirectionally tran s-
mitted over more than 100 km in an i nstall ed fiber-optic network
Manuscript received September 15, 2012; revised November 10, 2012,
November 30, 2012; accepted De cem be r 02, 2012. Date of publication De-
cember 10, 2012; date of current version January 09, 2013. This work was
supported in part by the National N atural Science Foundation of China under
Grant 61078003, Grant 60978003, Grant 11004161, Grant 61178011, and
Grant 6 1275116, in part by the Natural Science Foundation of Chongqing
City under Grant 2010BB9125, and Grant 2012jjB40011, in part by the O pen
Research Program of State Key Laboratory of Millimeter Waves of China
under Grant K201311.
J.Wu,Y.Liu,L.Fan,X.Tang,andG.XiaarewiththeSchoolofPhysics,
Southwest University, Chongqing 400715, China (e-mail: gqxia@swu.edu.cn).
Z. Wu is with the School of Physics, Southwest University, Chongqing
400715, China, and also with the S tate Key Lab of Millimeter Wav es, Southeast
University, Nanjing 210096, China (e-mail: zmwu@swu.edu.cn).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Dig
ital Object Identifier 10.1109/JLT.2012.2232283
[12]. Howev er, unidirectional information transmission is stil l
inadequate, and bidirectional chaos comm unication is always
high
ly expected since messages can be transmitted interactively.
In recent years, many configurations hav e been proposed to
realize bidirectional chaos communication [14]–[22]. These
configu
rations can mainly be div ided into two categories: one
is based on the chaos synchronization between two mutually
coupled SLs (MC-SLs) [14]–[17]; the other is based o n the
chaos
synchronization between two SLs driven by a common
force, that is to say, there is no direct coupling between them.
For two SLs without direct coupling between them, the chaos
sync
hronization between them can be realized under the case
that they are simultaneously injected by two complex chaos
(or noise) signals fro m a driving chaotic laser [18]–[22] or
two s
ynchronized mutually coupled chaotic SLs [23]. For the
MC-SLs system, there exists a coupling optical path between
two lasers, which can be used to transmit message from the
tra
nsmitted side to the received laser. Based on chaos pass
filter (CPF) effect, message can be decoded at the receiver
side. H owever, for the system based on two SLs driven by a
com
mon signal , there is no dir ect coupling path b e tween the
two synchro nized lasers. As a result, the message encryption
and decryption schem e used in a MC-SLs system may not be
su
itable, and some other message encryption and d ecryption
techniques need be adopted.
At present, free-space bidirectional chaos communication has
bee
n proposed and investigated, and related results show that
message can be bidirectionally transported in a short distance
[15]–[17], [2 2]. However, we noted that long-distance bidirec-
tio
nal chaos com m u nication, which shou ld be a more interesting
topic, is paid little at tention. In this paper, based on chaos syn-
chronization of two SLs injected by two chaos signals from an
id
entical driving chaotic laser, a chaos communication system
allowing long-distance bidirectional optical fiber transmission
is proposed. For two 10 Gb/s messages, the performance o f bidi-
re
ctional message encoding and decoding is analyzed, and the
influence of lon g distance fiber channel on communication per-
formance and corresponding optimized scheme are given.
II. S
YSTEM CONFIGURATION
Fig. 1 is our proposed system configuration for long-distance
bid
irectional chaos communication. A driving laser (DL) is
routed into chaos by a delayed optical feedback under suitable
operating c o ndition. The chaotic signal output from the D L is
amp
lified by an erbium d oped fiber amplifier (EDFA), and then
divided into two beams by a 50/50 optical fiber coupler
.
One is injected into response laser 1 (RL1) through fiber lin k
1
, and the other is injected into response laser 2 (RL2)
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