Time delay signature concealment of chaotic
semiconductor laser subject to nonlinear feedback
Chenpeng Xue (薛琛鹏), Ning Jiang (江 宁)*, Yunxin Lv (吕韵欣), and Kun Qiu (邱 昆)
Key Laboratory of Optical Fiber Sensing and Communications, Ministry of Education,
University of Electronic Science and Technology of China, Chengdu 611731, China
*Corresponding author: uestc_nj@uestc.edu.cn
Received May 24, 2016; accepted July 19, 2016; posted online August 9, 2016
An external-cavity semiconductor laser with nonlinear optical feedback to generate broadband chaos with time
delay signature (TDS) suppression is investigated. The system is composed of three semiconductor lasers, one of
which is regarded as the chaos generator, while the other two play a role of a built-in nonlinear modulator in the
external cavity of the generator. The results show that by properly setting the feedback strength and time
delay of the first semiconductor laser in the nonlinear modulator, the TDS embedded in the intensity and phase
time-series of the chaos can be effectively concealed in a wide range of frequency detuning.
OCIS codes: 140.1540, 140.5960, 190.3100.
doi: 10.3788/COL201614.091404.
Chaos generated by the external-cavity semiconductor la-
ser (ECSL) with delayed optical feedback has drawn con-
siderable attention for its potential applications in many
fields, such as secure communication
[1–4]
, fast random bit
generators (RBGs)
[5–8]
, chaotic lidar/radar
[9,10]
, and optical
time domain reflectometer (OTDR)
[11]
. Although the
ECSL with a delayed optical feedback can easily generate
broadband and high complexity chaotic signals, the chaos
usually also shows an obvious time delay signature (TDS),
which is undesirable in some of the applications. For
chaos-based secure communication, the security is majorly
dependent on the difficulty of the identification of the
emitter parameters, especially the time delay, which
can provide one of the possible clues for the attackers
to reconstruct the chaotic carrier
[12]
. For the RBGs, the
recurrence feature of the physical source indu ced by the
TDS would reduce the randomness of the RBGs
[5,6]
.
On one hand, technologies, such as power spectrum
analysis, auto-correlation function (ACF), delayed mu-
tual information (DMI), and permutation entropy (PE),
have been widely used to observe the TDS embedded in
the chaotic signal
[13–15]
. Besides, it is also reported that
the TDS can be successfully retrieved by computing the
same quantifiers from the phase time-series
[16]
. On the
other hand, a lot of schemes for the purpose of TDS con-
cealment are also reported
[17–26]
. For instance, Wu et al.
found that the semiconductor laser (SL) that is subject
to double delayed feedback loops can effectively suppress
the TDS in the chaotic signal
[18]
. Nguimdo et al. predicted
that the TDS could be lost simultaneously in the intensity
and phase dynamics of semiconductor ring lasers with
cross optical feedback
[19]
.Liet al. reported that fiber
Bragg grating feedback can be used to suppress the
TDS
[20]
. All of these studies motivate further investiga-
tions on the TDS concealment of chaotic SLs for its
potential applications in the physical secure communica-
tions and RBGs.
Very recently, the scheme that a ring of three unidirec-
tionally coupled SLs can be used to suppress the TDS
in both the intensity and phase space of chaos has been
numerically demonstrated
[25]
. However, the physical prin-
ciples of TDS concealment in the system are not provided
and the TDS concealment can be further investigated. In
this Letter, we proposed an advanced system in which a
ring of three unidirectionally coupled SLs with optical
feedback are adopted to generate chaos with the TDS
eliminated. The ACF and DMI of the intensity and phase
time-series are calculated to identify the TDS in the cha-
otic signal. According to our results, by making use of the
feedback term in SL2, the TDS embedded in the intensity
and phase time-series of chaos in SL1 can be effectively
suppressed.
The structure of the system composed of three SLs is
depicted in Fig.
1. In the system, SL1 is regarded as
the chaos signal source, its output is unidirectionally in-
jected into SL2; then, the output of SL2 is unidirectionally
injected into SL3; finally, the output of SL3 is unidirec-
tionally injected back into SL1. Here, SL2 and SL3 are
equivalent to a nonlinear modulator which can suppress
the TDS of the chaotic signal induced by the fixed
period stemming from the fixed-length external cavity.
Fig. 1. Structure of the proposed laser ring. CIR, optical circu-
lator; OC, optical coupler; OI, optical isolator; VA, variable
attenuator.
COL 14(9), 091404(2016) CHINESE OPTICS LETTERS September 10, 2016
1671-7694/2016/091404(5) 091404-1 © 2016 Chinese Optics Letters