Pulse reference-based compensation technique for
intensity-modulated optical fiber sensors
Qiang Bian (卞 强)
1,2
, Zhangqi Song (宋章启)
1,
*, Yuzhong Chen (陈宇中)
1
,
and Xueliang Zhang (张学亮)
1
1
Academy of Ocean Science and Engineering, National University of Defense Technology, Changsha 410073, China
2
College of Optoelectronics Science and Engineering, National University of Defense Technology,
Changsha 410073, China
*Corresponding author: songzhangqi@nudt.edu.cn
Received September 20, 2017; accepted November 1, 2017; posted online November 20, 2017
We propose a compensation technique based on pulse reference for intensity-modulated optical fiber sensors that
can compensate the power fluctuation of the light source, the change of optical components transmission loss,
and the coupler splitting ratio. The theoretical principle of this compensation technique is analyzed and a
temperature sensor based on fiber coating-covered optical microfiber is carried out to demonstrate the
compensation effect. The system noise is measured to be 0.0005 dB with the temperature sensitivity reaching
−0.063 dB∕°C, and the output drift is 0.006 dB in 2 h at room temperature. The output shows a slight variation
(0.0061 dB) when the light source and the common light path suffer a 3 dB attenuation fluctuation.
OCIS codes: 060.2370, 060.4080, 280.6780.
doi: 10.3788/COL201715.120603.
Intensity-modulated optical fiber sensors (IM-OFSs) are
one of the most important and earliest developed OFSs
for their simplicity, using inexpensive light sources, and
potential low cost. In past decades, IM-OFS have been
well studied to detect several types of physical quantities
such as displacement
[1]
, temperature
[2,3]
, bending
[4]
, strain
[5]
,
magnetic field intensity
[6]
, and others
[7,8]
. However, owing
to directly using optical intensity as the information
carrier, IM-OFSs have the problem that the output might
be affected by the fluctuation of the light source, the
change of optical components transmission loss, and
the coupler splitting ratio, as well as other factors with
time and external perturbations. Many compensation
techniques were proposed to solve this problem: the light
source negative-feedback compensation technique
[9]
,
the light split compensation technique
[3,10]
, the twin-
receiving-fiber compensation technique
[11]
, the dual-
wavelength compensate technique
[12]
, the network-based
compensation technique
[13]
, and the neural-network com-
pensation technique
[14]
. The performances of the IM-OFSs
were improved
[15–19]
but there still exist some unavoidable
problems for the compensation techniques mentioned
above. For example, though the light split compensation
technique can compensate the fluctuation of the light
source, it cannot solve the splitting ratio fluctuation
caused by the optical splitter itself. The network-based
compensation technique can avoid the splitting ratio fluc-
tuation problem, but it introduces more optical compo-
nents transmission loss fluctuation problems.
In this Letter, we propose a compensation technique
based on pulse reference. This compensation technique
can compensate the power fluctuation of the light source,
the change of optical components transmission loss, and
the coupler splitting ratio, while at the same time keeping
the structure simple and the design flexible for a wide
application range. Another advantage of this compensa-
tion technique is that it is completely compatible with
optical time division multiplexing system, which can inte-
grate a large number of sensors and decrease the cost of per
sensor. After the explanation of this technique, an optical
microfiber tempe rature sensor was carried out to demon-
strate the good compensation effect of this technique.
The schematic diagram of the pulse reference-based
compensation technique is shown in Fig.
1. A light pulse
emitted by the light source is divided into two light pulses
(signal pulse and reference pulse) by the 2 × 2 fiber optic
coupler. These two pulses will both come back again to the
coupler after being transmitted and reflected by their
respective fiber and reflector. Then the detector will
receive two pulses and transform them into electrical
signals. The signal processing unit is responsible for
converting them into digital signals and analyzing these
signals.
The time delay Δt between the signal pulse and refer-
ence pulse depends on the relative length of the sensing
fiber and delay fiber. For the purpose of distinguishing
these two pulses in the time domain, Δt is supposed to
Fig. 1. Schematic diagram of the pulse reference-based compen-
sation technique.
COL 15(12), 120603(2017) CHINESE OPTICS LETTERS December 10, 2017
1671-7694/2017/120603(4) 120603-1 © 2017 Chinese Optics Letters
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