Three-dimensional imaging lidar system based on high
speed pseudorandom modulation and photon counting
Yufei Zhang (张宇飞)
1,2
, Yan He (贺 岩)
1,
*, Fang Yang (杨 芳)
3
,
Yuan Luo (罗 远)
1,2
, and Weibiao Chen (陈卫标)
1,
**
1
Key Laboratory of Space Laser Communication and Detection Technology, Shanghai Institute of Optics and
Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
2
University of Chinese Academy of Sciences, Beijing 100049, China
3
School of Electronics and Information Engineer, Shanghai University of Electric Power, Shanghai 200090, China
*Corresponding author: heyan@siom.ac.cn; **corresponding author: wbchen@mail.shcnc.ac.cn
Received March 31, 2016; accepted September 9, 2016; posted online November 5, 2016
High speed pseudorandom modulation and photon counting techniques are applied to a three-dimensional
imaging lidar system. The specific structure and working principle of the lidar system is described. The actual
detector efficiency of a single-photon detector in an imaging system is discussed, and the result shows that a
variety of reasons lead to the decrease in detection efficiency. A series of ranging and imaging experiments are
conducted, and a series of high-resolution three-dimensional images and a distance value of 1200 m of nonco-
operative targets are acquired.
OCIS codes: 110.6880, 280.3400, 030.5260.
doi: 10.3788/COL201614.111101.
There is an increasing need for three-dimensional imaging
systems to acquire range and surface profile data for a
number of industrial and defense app lications
[1]
. In recent
years, a lot of three-dimensional imaging systems based
on different technology have been proposed
[2,3]
. Among
the many methods, pseudorandom (PN) code lidar is a
low-power approach to active range resolution and three-
dimensional imaging. Traditional three-dimensional imag-
ing systems are mostly composed of low-frequency, high-
energy short-pulse-width lasers, large receiver telescopes,
and linear detectors
[4,5]
. However, such a system requires
high peak power of the laser to achieve long range imag-
ing
[6,7]
. Compared to mono-pulse lidar transmitters, the de-
mand for peak power is reduced when a continuous wave
laser is modulated by a PN code. So, it can effectively re-
duce the power consumption, volume, and requirements of
the heat dissipation. Because of this advantage, many
simulations and experimental investigations on PN code
lidar were conducted in ranging or imaging systems
[8–12]
.
PN codes have great potential in applications because
of their randomness, sharp autocorrelation, and small
cross-correlation value. The PN receiver can measure
the signal propagation time and target impulse response
by correlating the received signal with the transmitted
ones and determining the peak location of the correlation
function
[13]
.
A single-photon detector is sensitive enough to detec t
the weakest light, which allows the lidar system to be op-
erated in an eye-safe level. In recent years, a lot of work on
photon counting laser ranging has been done
[14–17]
. From
these works, we can see that these systems need a long
pixel dwell time to achieve a histogram. The pixel dwell
time of a PN code lidar only depends on the range ambi-
guity and pulse repetition frequency. Thus, photon
counting technology in conjunction with PN codes allows
for the lower peak power laser illumination and shorter
pixel dwell time.
A series of experiments of PN codes were performed
in the previous work of our laboratory, and were primar-
ily concerned with the demonstration of the basic
principle
[18,19]
. Recently, a series of experiments of three-
dimensional imaging lidar systems using these principles
has been conducted. A schematic of the system compo-
nents are shown in Fig.
1. A PN code generator, a module
of a field-programmable gate array (FPGA) capable of
producing 1024 bits of M sequence PN codes at 1 GHz
modulation rate and 10 kHz repeating rate, was connected
to an optical communication module. The modulated di-
ode laser wa s amplified by a three-stage fiber amplifier,
and the average power of the final output laser is
260 mW. The laser’s output is steered in a horizontal
and vertical direction by tow motor-driven scanning re-
flectors. The horizontal scanning angle is 360°, while
the vertical scanning angle depends on the mechanical
structure of the optical system. Angle information was ob-
tained by the encoder and transmitted to the FPGA. The
return photons took the same co-axial optical path back to
the receiving optical system, passed through a 10 nm
band-pass filter centered at 1550 nm with a diameter of
50 mm to restrict background noise, and launched into
a single mode fiber. The fiber was connected to the
single-photon detector, providing electrical photon signals
to the FPGA. The optical transmitting and receiving sys-
tem is shown in Fig.
2. Stratix V, a high-performance
FPGA, was used in the system to achieve photon
counting and correlation. The program of the FPGA
was designed in multithreaded architecture, which allows
the simultaneous acquisition, mathematical operation,
COL 14(11), 111101(2016) CHINESE OPTICS LETTERS November 10, 2016
1671-7694/2016/111101(5) 111101-1 © 2016 Chinese Optics Letters