Large-range displacement measurement using sinusoidal
phase-modulating laser diode interferometer
Ming Zhang (张 鸣)
1,2,
*, Chang Ni (倪 畅)
1,2
, Yu Zhu (朱 煜)
1,2
, Leijie Wang (王磊杰)
1,2
,
Chuxiong Hu (胡楚雄)
1,2
, and Jinchun Hu (胡金春)
1,2
1
State Key Laboratory of Tribology, Department of Mechanical Engineering, Tsinghua University,
Beijing 100084, China
2
Beijing Laboratory of Precision/Ultra-Precision Manufacture Equipment and Control, Tsinghua University,
Beijing 100084, China
*Corresponding author: zm01@mails.tsinghua.edu.cn
Received April 23, 2017; accepted June 16, 2017; posted online July 11, 2017
A signal processing method of realizing a large-range displacement measurement in a sinusoidal phase-
modulating laser diode interferometer is proposed. The method of obtaining the dynamic value of the effective
sinusoidal phase-modulating depth is detailed, and the residual amplitude modulation is also taken into account.
Numerical simulations and experiments are carried out to compare this method with the traditional one.
We prove that, with this method, the sinusoidal phase-modulating laser diode interferometer can realize a
centimeter-level displacement measurement range with high precision, which is much better than the traditional
method.
OCIS codes: 120.3180, 070.6020, 350.2460.
doi: 10.3788/COL201715.101201.
The sinusoidal phase-modulating laser diode (SPM-LD)
interferometer has been used for vibration sensing and
displacement measurement because of unique features
such as simplicity and good expansibility
[1–17]
. However,
the measurement range of this interferometer is limited
to a few micrometers because an important parameter,
the effective SPM depth, is considered to be a constant
in conventional signal processing
[1–3]
. The effective SPM
depth actually is linear to the length difference between
the reference arm and the measurement arm in the
SPM-LD interferometer
[4,5]
. As a result, the traditional
method would result in great errors in the large-range
displacement measurement. Therefore, to realize the
large-range displacement measurement accurately, special
methods are required to get the dynamic value of the
effective SPM depth. Some patents set the effective
SPM depth as a small number and apply the equivalent
infinitesimal replacement method to estimate its dynamic
value
[6–9]
. This is very useful , but because of the small num-
ber set as the effective SPM depth, the amplitudes of the
harmonics extracted from the interference signal could be
very small, which would give a low signal-to-noise ratio
(SNR) and limit the entire measurement accuracy. In
addition, the sinusoidal modulation of the frequency in-
volves a residual amplitude modulation (RAM) to the la-
ser, which would also cause errors and need to be taken
into account
[10,11]
.
In this Letter, a novel sig nal proce ssing method is pro-
posed to improve the performance of a large-range dis-
placement measurement in the SPM-LD interferometer
by obtaining the dynamic value of the effective SPM
depth. Numerical simulations and experiments are carried
out to compare the novel method with the traditional one.
The simulation and experimental results prove that the
displacement measurement range of the SPM-LD interfer-
ometer can be enlarged to the centimeter level with high
precision.
Figure
1 shows the structure of the SPM-LD interferom-
eter for the large-range displacement measurement.
The light from the laser, whose frequency is modulated
by the SPM signal from the signal generator, is emitted by
the collimator after it goes through the isolator. The fre-
quency modulation of the laser leads to a phase modula-
tion term in the interference signal
[4,5]
. The laser is split
into two parts by the beam splitter (BS). One part, which
is reflected by the reference mirror, serves as a reference
wave. The other part, which is reflected by the object
mirror, serves as a measurement wave. The reference wave
and measurement wave are recombined by the BS and
interfere with each other. And, the interference signal is
detected by the photoelectric detector (PD) and acquired
Fig. 1. Structure of the SPM-LD interferometer for the large-
range displacement measurement.
COL 15(10), 101201(2017) CHINESE OPTICS LETTERS October 10, 2017
1671-7694/2017/101201(5) 101201-1 © 2017 Chinese Optics Letters
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