Optical pulse compression reflectometry based on single-sideband
modulator driven by electrical frequency-modulated pulse
Weiwen Zou
a,b,
n
, Lei Yu
a
, Shuo Yang
a
, Jianping Chen
a,b
a
State Key Laboratory of Advanced Optical Communication Systems and Networks, Department of Electronic Engineering, Shanghai Jiao Tong University,
Shanghai 200240, China
b
Shanghai Key Lab of Navigation and Location Services, Shanghai Jiao Tong University, Shanghai 200240, China
article info
Article history:
Received 22 December 2015
Received in revised form
12 January 2016
Accepted 13 January 2016
Available online 4 February 2016
Keywords:
Fiber optics sensors
Frequency modulation
Optical pulse compression reflectometry
abstract
We propose a novel scheme to generate a linear frequency-modulated optical pulse with high extinction
ratio based on an electrical frequency-modulated pulse and optical single-sideband modulator. This
scheme is proved to improve the stability and accuracy of optical pulse compression reflectometry
(OPCR). In the experiment, a high spatial resolution of 10 cm and a long measurement range of 10.8 km
using a laser source with 2-km coherence length are demonstrated.
& 2016 Elsevier B.V. All rights reserved.
1. Introduction
Optical fiber reflectometry is an important instrument to
monitor intrinsic or external disturbance in optical fibers [1].
Different types of reflectometries have been proposed [2–5]. The
first type of optical time domain reflectometry (OTDR) dates back
to 1970s [2], which has been widely used for long-length inter-
rogation although its spatial resolution was limited due to the
required pulse energy and the intrinsic fiber attenuation. Another
reflectometry, called optical frequency domain reflectometry
(OFDR) [3], was developed to overcome such shortage since it is
referred to the frequency modulation continuous wave (FWCW)
radar technology. However, the measurement range of OFDR is
physically limited by the half of coherence length of the laser
source. In comparison, optical coherence domain reflectometry
(OCDR) [4] and optical low coherence reflectometry (OLCR) [5] can
also provide competitive spatial resolution but the measurement
range is confined as well. Most recently, we proposed a new
reflectometry inspired by pulse-compression radar [6], named
pulse-compression OTDR [7] or optical pulse compression
reflectometry (OPCR) [8], which can overwhelm the tradeoff
between the spatial resolution and measurement range. An optical
pulse with a long pulse duration and linear frequency modulation
(LFM) is launched into an optical fiber and the backscattered light
is coherently detected using matched filtering so as to significantly
compress the original pulse duration. Consequently, OPCR is able
to achieve a high spatial resolution and large signal to noise ratio,
both of which are attributed to the wide LFM bandwidth.
In this work, we demonstrate a new-scheme OPCR by use of
one optical single-sideband modulator (SSBM) and an electrically
pulsed linear frequency modulation. Compared with the previous
scheme based on two modulators [8], the new scheme can
generate the electric pulsed LFM and optical LFM pulse with
less complexity, broader bandwidth and larger extinction ratio.
We successfully achieve 10 cm spatial resolution over 10.8 km
measurement range although a laser source with coherence length
of only 2 km is used.
2. Principle and experimental setup
Fig. 1 compares two schemes generating an optical LFM pulse
for the OPCR with different extinction ratio. In both cases, an ar-
bitrary waveform generator (AWG) is used to generate two syn-
chronous electric waveforms of rectangular pulse and sawtooth.
The period of the sawtooth is equal to the width of the rectangular
pulse. In the original scheme [see Fig. 1(a)] [8], the sawtooth is
connected with a voltage controlled oscillator (VCO) that drives a
single sideband modulator (SSBM) to generate an LFM continuous
light; the electric pulse is launched to a Mach–Zehnder modulator
(MZM) so as to achieve an optical LFM pulse with finite (typically,
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journal homepage: www.elsevier.com/locate/optcom
Optics Communications
http://dx.doi.org/10.1016/j.optcom.2016.01.034
0030-4018/& 2016 Elsevier B.V. All rights reserved.
n
Corresponding author at: State Key Laboratory of Advanced Optical Commu-
nication Systems and Networks, Department of Electronic Engineering, Shanghai
Jiao Tong University, Shanghai 200240, China.
E-mail address: wzou@sjtu.edu.cn (W. Zou).
Optics Communications 367 (2016) 155–160