High-speed optical secure communication
with external noise source and internal
time-delayed feedback loop
YUDI FU,MENGFAN CHENG,* XINGXING JIANG,QUAN YU,LINBOJIE HUANG,LEI DENG, AND DEMING LIU
National Engineering Laboratory for Next Generation Internet Access System (NGIA), School of Optical and Electronic Information,
Huazhong University of Science and Technology (HUST), Wuhan 430074, China
*Corresponding author: Chengmf@mail.hust.edu.cn
Received 3 July 2019; revised 7 September 2019; accepted 10 September 2019; posted 11 September 2019 (Doc. ID 371592);
published 31 October 2019
We propose and experimentally demonstrate a novel physical layer encryption scheme for high-speed optical
communication. A 10 Gb/s on-off keying signal is secretly transmitted over 100 km standard single-mode fiber.
The intensity-modulated message is secured by the encryption mechanism, which is composed of an external noise
source and an internal time-delayed feedback loop. The external noise serves as an entropy source with sufficient
randomness. The feedback loop structure in the transmitter introduces a time-domain encryption key space, and a
corresponding open-loop configuration at the receiver side is used for synchronization and decryption.
Experiment results show the effectiveness of the proposed scheme. For a legitimate terminal, bit error rate below
10
−8
can be obtained. Decryption degradations with the mismatch of different hardware parameters are re-
searched. The time delay in the feedback loop provides a sensitive encryption key. For other hardware parameters,
the system is robust enough for synchronization. Meanwhile, the time-delay signature of the loop is able to be well
concealed by the external noise. Moreover, the proposed scheme can support density wavelength division multi-
plexing transmission with a relatively simple structure. This work also provides a new concept to establish optical
secure communication by combining a time-delayed feedback chaotic system and random noise.
© 2019 Chinese
Laser Press
https://doi.org/10.1364/PRJ.7.001306
1. INTRODUCTION
With the explosive growth of data information and knowledge,
optical-fiber communication is developing towards high-speed,
broadband, and large-capacity communication networks. It will
be difficult to meet the requirements of high-capacity data
transmission and information security simultaneously. The
security performance of traditional strategies such as cryptog-
raphy and authentication protocols at the media access control
layer or higher layers is potentially limited by the processing
speed of electronics and the capacity of optical networks
[1,2]. In the past decade, secure optical communication with
a physical layer protection technique such as optical encryption
and steganography has been developed [3–6]. These optical do-
main strategies can support high throughput and further en-
hance the security of communication systems.
Conceptually, encryption at the physical layer is to bury a
plain-text signal into a random or pseudo-random signal in
various ways. Therefore, an entropy source with sufficient ran-
domness or complexity is indispensable. As a typical noise
source in an optical field, amplified spontaneous emission
(ASE) noise has been used as an ultrawideband entropy source
in secure communications [7–9]. In these schemes, noise em-
bedded with data and a pure noise signal are transmitted
through the fiber link with a time difference. At the receiver
side, only when the time delay is accurately fixed can the data
signal be extracted by canceling the noise. The data signal is
well hidden within the noise in both time and frequency do-
mains. The broadband nature of ASE noise makes the time
delay a very sensitive encryption key. An optical delay line
(DL) with highly adjustable precision enables a legal receiver
to match the key precisely. As a result, a time domain large
key space can be established [ 10]. However, the interference
mechanism degrades the optical signal-to-noise ratio (OSNR)
and suppresses the maximum data transfer rate of a single wave-
length to 1 Gb/s [11]. Besides, beating the modulated ASE and
the reference ASE from different light paths might impact the
stability of data decryption. Thus, the decryption can be held in
just several seconds because of the sensitive interference struc-
ture [7]. Meanwhile, the time delay could be extracted by an
unauthorized third party using some statistical methods, such
as cross-correlation function or delayed mutual information.
1306
Vol. 7, No. 11 / November 2019 / Photonics Research
Research Article
2327-9125/19/111306-08 Journal © 2019 Chinese Laser Press