Hybrid LD and LED-based underwater optical
communication: state-of-the-art, opportunities,
challenges, and trends [Invited]
Xuan Huang (黄 璇)
1
, Fang Yang (杨 昉)
1,2,
*, and Jian Song (宋 健)
1,2
1
Department of Electronic Engineering, Tsinghua University & Beijing National Research Center for Information Science
and Technology (BNRist), Beijing 100084, China
2
Key Laboratory of Digital TV System of Guangdong Province and Shenzhen City, Research Institute of Tsinghua
University in Shenzhen, Shenzhen 518057, China
*Corresponding author: fangyang@tsinghua.edu.cn
Received June 29, 2019; accepted August 2, 2019; posted online August 29, 2019
In this paper, the current research of an underwater optical wireless communication (UWOC) network is
reviewed first. A hybrid laser diode (LD) and light-emitting diode (LED)-based UWOC system is then pro-
posed and investigated, in which hybrid cluster-based networking with mobility restricted nodes is utilized to
improve both the life cycle and throughput of the UWOC network. Moreover, the LEDs are utilized for the
coarse alignment, while the LDs are used for high-precision positioning to reduce the difficulty of optical
alignment. Finally, challenges and trends for UWOC are pointed out to provide some insight for potential
future work of researchers.
OCIS codes: 100.6640, 210.4770, 180.1790.
doi: 10.3788/COL201917.100002.
1. INTRODUCTION
With the development of the economy, the modern marine
high-tech research, such as marine resources development,
oceanographic research, seabed survey, and detection, has
become a new research field in the world, and the research
on related marine scientific technology has become the
crucial issue for all countries in the world
[1]
. Underwater
wireless communication technology is the basis and guar-
antee for the realization of ocean observation, resource
detection, and environmental monitoring. Therefore, it
is urgent to develop highly reliable and high-speed under-
water wireless communication technology to process large
amounts of underwater data with the latency as low as
possible
[2]
.
At present, underwater wireless communication technol-
ogy mainly includes underwater wireless electromagnetic
communication, underwater acoustic communication, and
underwater optical communication
[3]
.However,theelectro-
magnetic waves suffer from great attenuation in the water
because of the absorption and scattering effects, which
makes communications with electromagnetic waves under-
water almost impossible
[4]
. Different from the electromag-
netic wave, the acoustic wave has low loss in the water,
which means its communication range in the water can
be very long
[5]
. However, it also has several disadvantages.
The acoustical communication channel has a narrow band-
width, which means it can only handle a relatively low bit
rate
[6]
. In addition, an acoustic wave is greatly affected
by environmental factors such as sea water temperature,
salinity, and pressure compared with underwater optical
communication. Then, multi-path transmission is prone
to occur, resulting in signal amplitude attenuation and
inter-symbol interference, which seriously affects the
establishment of communication processes
[7]
. Moreover,
underwater acoustic signals are easy to be monitored,
and it is difficult to meet the requirements of confidential-
ity in the communication process. Also, the acoustic wave
speed in water is about 1500 m/s, which is slow and will
lead to high latency in communication
[8]
. Thus, in order
to accommodate a higher bit rate, another underwater
wireless communication scheme with wider bandwidth
should be investigated. A possible candidate is optical
wireless communication. Specifically, for underwate r opti-
cal wireless communication (UWOC), the blue/green
light wavelengths are usually utilized because they suffer
less attenuation in water compared to other colors. There
are several advantages for the UWOC. The first is the
high speed and wide spectrum. Because of the high fre-
quency of the light wave and its strong information carry-
ing capability, it can realize large-capacity underwater
data transmission. The transmission bandwidth of light
waves in water can reach hundreds of megahertz, which
makes it possible to transmit large-capacity data quickly
under wa ter. The second advantage is the superior secu-
rity. Optical communication has the characteristics of no
electromagnetic radiation and strong anti-interference
ability, resulting in the good underwater electronic
countermeasure performance. The third advantage is
the small size. Short wavelengths can greatly reduce the
size and weight of transmitting and receiving equip-
ment. The last advantage is the low power consumption.
COL 17(10), 100002(2019) CHINESE OPTICS LETTERS October 2019
1671-7694/2019/100002(9) 100002-1 © 2019 Chinese Optics Letters