a) b) c)
d) e) f)
Like optical fiber communications, wave-length-division multiplexing using differ-
ent-colored LEDs also allows the bandwidth to grow proportionally with the
number of wavelengths. Smart transmit-
ters and receivers that emit beams transmitting different codes, pointing in different
directions, allows Code Division Multiple
Access (CDMA) techniques similar to cell
phone communications. 3 We have also
demonstrated a microelectromechanical
(MEMS)-based retroreflecting modulator
with sufficient bandwidth for video rates
and software-defined radio using quadrature amplitude modulation (QAM). 4, 5
Most optical wireless links have been
experimental efforts taking place in
tanks or pools. Commercially, Ambalux
(Tucson, AZ) demonstrated a 10 Mbit/s
system with a range of 40 m and lists
options for their optical transceivers at
100 Mbit/s and 1 Gbit/s transmission
rates. Technology developed by the Woods
Hole Oceanographic Institute (Woods
Hole, MA) has transitioned to Sonardyne
(Yateley, England), which now lists two
BlueComm [trademarked] systems using
LEDs for 10 m at 1–5 Mbit/s, 150 m at
1–12. 5 Mbit/s, and a 7 m laser-based system at 500 Mbit/s.
In the past year, several researchers
have also performed tank experiments
that start to push the limits of optical wireless communications in the laboratory us-
ing 16 QAM orthogonal frequency divi-
sion multiplexing (OFDM) to achieve data
rates in excess of 7 Gbit/s in seawater for
ranges of 4 to 8 m. 6, 7 This suggests that
optical wireless communication technology is rapidly maturing and that experiments need to move from tanks in laboratories and out to sea.
In general, as humans begin to more
efficiently exploit undersea resources, an
increased network of undersea pipelines,
vehicles, divers, and robots will need to
operate together to inspect, repair, and
maintain underwater equipment. Multiple
modes of communications will be required
and hybrid systems that seamlessly con-
vert between acoustic, fiber-optic, RF, and
underwater FSO communications will be-
come increasingly important.
In this emerging undersea world, wired
communication and power cables will
connect underwater fixed infrastructure
and tethered vehicles, sonar and RF will
serve subsea platform-to-shore communi-
cations, and underwater FSO architectures
will provide a vital, niche communications
role by offering high-bandwidth, short-
range communications between fixed and
moving assets like underwater autono-
mous remotely operated vehicles (ROVs)
and divers (see Fig. 4).
REFERENCES
1. B. Cochenour and L. Mullen, “Channel
response measurements for diffuse non-line-of-sight (NLOS) optical communication
links underwater,” Proc. IEEE/MTS OCEANS,
Waikoloa, HI (Sep. 2011).
2. J. A. Simpson et al., “ 5 Mbps optical wireless
communication with error correction coding
for underwater sensor nodes,” Proc. IEEE/MTS
OCEANS, Seattle, WA (Sep. 2010).
3. J. A. Simpson et al., IEEE J. Sel. Area. Comm.,
30, 5, 964–974 (Jun. 2012).
4. W. C. Cox et al., “A MEMS blue/green
retroreflecting modulator for underwater
optical communications,” Proc. IEEE/MTS
OCEANS, Seattle, WA (Sep. 2010).
5. W. C. Cox et al., “Underwater optical
communication using software defined
radio over LED and laser based links,” Proc.
IEEE Military Communications Conference
(MILCOM), Baltimore, MD, 2057–2062 (Nov.
2011).
6. H. H. Lu et al., IEEE Photon., 8, 5, 7906107
(Oct. 2016).
7. T. C. Wu et al., Sci. Rep., 7, 40480 (Jan. 2017).
John Muth is a professor in Electrical and
Computer Engineering at North Carolina
State University, Raleigh, NC; e-mail:
muth@ncsu.edu; www.ece.ncsu.edu.
FIGURE 3. Examples of undersea optical communications equipment include a compact 1–5 Mbit/s optical system in a pool test on an
autonomous underwater vehicle (a); a compact 1–5 Mbit/s optical transmitter (b); a smart transmitter that sends CDMA-coded signals in
directed beams (c); a 1–5 Mbit/s LED optical transmitter with error correction coding provided by an FPGA (d); an optical receiver with FPGA (e);
and a 5 Mbit/s optical buoy in turbid water (f).
