International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 6, June 2013
ISSN 2319 - 4847
Design and Implementation of Under Water
Optical Communication System
Ziad T. Al Dahan 1 , Samar Y. Al Dabagh 2 and Asmahan Assad3
1
Department of medical engineering ,Nahrain university , Baghdad
Department of physics, college of science for women, Baghdad University, Baghdad
2,3
Abstract:
The design and implementation of underwater optical communication system is presented. The system consists of transmitter,
water channel, and receiver. The laser diode used as a transmitter at 532 nm wavelength in CW mode with 50 mw power. The
channel is about glass pool its dimensions (1m, 0.5m, 0.5m) with different samples of water (distilled, Tigris, Euphrates, and
Shat Al Arab). The receiver consists of photodiode detector and amplification circuit. This system transmits data from PC to
another PC through water channel at different samples. The result shows the difference in the received signal at different tested
water samples.
Key words : underwater communication , laser , Max232 IC
1. Introduction:
Communication is transmission, reception, and processing of information using electronic circuits.
Information is defined as knowledge can be in an analog form (continuous) such as human voice, video picture
information, or in digital form (discrete steps) such as binary – coded numbers, alpha numeric codes, graphics
symbols, micro processor op-codes, or data base in information.
All the information must be converted to electromagnetic energy before it can be propagated through an electronic
communication system.
Fig (1) is a simplified block diagram of an electronic communication system showing the relationship among the
original source information, the transmitter, transmission medium, the receiver, and the received information at the
destination [1]-[2].
Figure (1) block diagram of an electronic communication system [2]
Optical communication is one of the most promising ways to achieve highest receiver sensitivity , excellent spectral
efficiency and longest transmission distance for next generation of optical communication system [3].
Communication underwater is very challenging. Unlike terrestrial communication links, radio frequencies and
microwaves do not propagate through water. Acoustics communication links have been of keen interest for underwater
applications in the past few decades, but provide limited bandwidth [4].
Laser based communication using blue-green lasers is a potential technique for high bandwidth underwater wireless
communication because of its high data transfer rate, reasonably large range, small size, low power consumption,
immunity to interference and jamming and covertness of transmission. Underwater communication system using blue
green laser may be used for transmitting any type of file (Video, Audio, PPT, DOC, PDF and EXE) from one platform
to the other [4].
Volume 2, Issue 6, June 2013
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 6, June 2013
ISSN 2319 - 4847
Figure (2) Absorption Coefficient of pure seawater [4]
Laser propagation in sea water can be shown by the graph between absorption coefficient and wavelength in (Fig. 2).
Sea water has transmission window between blue-green region and it varies with geographical location, distance from
the sea coast and depth below sea surface. The attenuation coefficient acquires a constant value below 200m of the sea
surface. Blue laser is suitable for deep sea water and green is suitable for coastal sea water. [6]
Most of laser cannot penetrate through the sea due to be absorbed by the sea, but the blue-green laser (the wavelength is
about 470 ~ 570nm) has the minimum energy fading in the sea, whose fading rate is about 0.155~0.5dB/m. Hence, the
blue-green laser can propagate from several hundreds of meters to kilometers in the sea, and this feature of blue-green
laser in the sea is said the window effect. Based on the window effect of blue-green laser [7].
Since the laser medium is line-of-sight and the beam being only several millimeters in diameter it is very difficult for
the data stream to be tapped. This offers secure communications since any attempts to intercept the laser beam would be
detected at the receiver as a loss in data. [8]
One attractive option for wireless communication in the underwater environment is underwater free-space optical
(FSO)communication, which refers to an underwater optical link, typically operating near the blue-green region of the
visible spectrum, that uses water as the propagation medium (i.e., no fiber). This emerging technology shows the
potential to augment existing underwater communication methods by providing high-data-rate wireless communication
over short-range links. [9]
In coastal waters with high turbidity and high content of organic matter, the green light attenuation is less than that for
blue laser light, making blue preferable for operations in clear water masses of the open ocean. [10]
Experimental work:
The completed system consists of two parts, first part capable of simultaneously transmitting information (transmitter).
Second part is able to receive transmitted signals (receiver).The electronic circuits of the system is express in figs. (3)
and (4).
The first part (transmitter) is an electronic circuit made by using laser diode, Max232 IC, capacitors, resistors, and
transistor. The circuit is connected to power supply (5volt) and PC by the RS 232 cable as shown in fig. (3).
Figure (3) The Transmitter Circuit
Volume 2, Issue 6, June 2013
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 6, June 2013
ISSN 2319 - 4847
The second part (receiver) is an electronic circuit. It is made of photodiode (as detector), Max232 IC, 1747IC,
capacitors, power supply (5volt), and RS232 cable to connect the circuit with PC shown in fig. (4).
Figure (4) The Receiver Circuit
The data are sent via the RS-232 standard interface with a bit rate of 110 Kbps from PC1 by line receiver to convert the
data from electrical levels (-12/+12 V) into TTL level (0/5 V). The intensity modulation on/off keying was the way to
modulate this data using laser diode that have 532nm wavelength. This laser source is used to convert the encoded data
from electrical levels into output optical power levels transmitting through water pool.
Laser as a communications medium has some unique properties compared to other forms of media. A line-of-sight laser
beam is useful where wires cannot be physically connected to a remote location. A laser beam, unlike wires, also does
not require special shielding over longer distances.
At the receiver side there is an optical receiver circuit which receives data using a photo diode and a MAX 232 IC used
to convert the TTL levels (0/5 V) to electrical levels (-12/+12 V). This IC includes a charge pump, which generates
±12V from a single 5V supply; also include two receivers and two transmitters in the same package.
Digital data from a PC1 can be transferred via RS-232 cable to a drive circuit of the transmitting unit of the
underwater communication system. A converter MAX 232 drives current which is responsible for the intensity
modulation of the laser beam. The transmitted laser beam passes a distance of one meter in the water pool before it is
arrive the photo detector. With the help of a detector, the optical signals are converted back to a digital data stream by
using MAX232.
The RS-232 standard supports two types of connectors – a 25-pin D-type connector (DB-25) and a 9-pin D-type
connector (DB-9). The type of serial communications used by PCs requires only nine pins. In RS-232 parlance, the
device that connects to the interface is called Data Communications Equipment (DCE) and the device to which it
connects is called Data Terminal Equipment (DTE). This standard was mainly designed to connect DTE that is sending
and receiving serial data (such as a computer) and DCE that is used to send data over long distances (such as a
modem).[8]
A Schmitt-trigger inverter 7414IC was used to invert the signal at the receiver side.
(a)
(b)
Fig. (5) communication system
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 6, June 2013
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a- block diagram
b- experimental setup
Results & Discussions:
The laser used in the transmitter circuit is a diode laser (p-n) junction semiconductor that emits light when forward
biased and optic power generated by LD is linearly proportional to the forward driving current, but LD needs a
threshold current and below this level there is a small increase in optic power with drive current [11]. The curve in
figure (6) shows the relationship between laser diode current and optical output power. Spontaneous emission occurs
prior to the threshold at (0.18 A), after the threshold current is exceeded, coherent emission occurs.
50
45
O u tp u t p o w e r (m w )
40
35
30
25
20
15
10
5
0
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Current (A)
Fig (6) Output power via current for laser diode
The attenuation of light by water is caused by two independent mechanisms, scattering and absorption which affect the
amplitude, phase, and arrival angle of the light beam [12].
The relation between input and output power through the different samples of water (Distilled, Tigris, Euphrates, and
Shat Al Arab) shown in figure (7). In this figure we notice that the distilled water (blue line) have the highest output
power because its clarity of salts, dissolved matter, organic matter which causes the absorption and scattering. While in
Shat Al Arab (green line), the curve show the lowest values of output power because it have high level of mud and
salts. Middle value of absorption noticed in Tigris River (pink line) and Euphrates River (red line) because they have
salts and organic dissolved matter but not high as in Shat Al Arab.
35
Di still ed
Ti gris
Euphrates
Shat Al Arab
Output power (mw)
30
25
20
15
10
5
0
0
10
20
30
40
50
Input power (mw)
Fig (7) Output power via input power for water samples
The figures (8, 9, 10, and 11) show the transmitted signal at part (a) and received signal at part (b) through the four
water samples. From these figures, we can notice that the amplitude of square wave differed with different samples of
water and delay shifting in the received signal. The figures shows that the higher the purity of water, the higher square
wave and delay time. This is due to the fact that less attenuation and scattering events are in the most pure water. The
increase in the organic matter and dissolved salts in (Tigris, Euphrates, and Shat Al Arab) waters increases the ability
of absorbing and scattering the laser light transmit throw the water and increase the delay time especially in Shat Al
Arab. This results show a loss in the receiving power of the received singles.
Volume 2, Issue 6, June 2013
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 6, June 2013
ISSN 2319 - 4847
Fig(8) The input and output signal of Distilled water
(a) Input signal 5v/Div, 500µs/Div.
(b) Output signal 5V/Div, 500µs/Div
Fig (9) the input and output signal of Tigris River
(a) input signal 2v/Div, 25µs/Div.
(b) Output signal 5V/Div, 25µs/Div.
Fig (10) the input and output signal of Euphrates River
(a) a- input signal 2v/Div, 25µs/Div.
(b) Output signal 5V/Div, 25µs/Div.
Fig (11) the input and output signal of Shat al Arab
(a) Input signal 2v/Div, 25µs/Div.
(b) Output signal 5V/Div, 25µs/Div.
Volume 2, Issue 6, June 2013
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 6, June 2013
ISSN 2319 - 4847
Conclusion:
1-The presented optical communication system is suitable for underwater communication, uses cheap and easily
available components, and can furthermore be used to reliably measure the distance between transmitter and receiver.
2- Communications based on EM wave transmission offer great benefits such as the increase of the data rate of the link
to transmit more information.
3- The best underwater communication for long haul link is through Tigris river .
References :
[1.] Wayne Tomasi, “Electronic communications system fundamental through advanced”, Pentice
Hall
Career & Technology , 2nd edition, 1994.
[2.] Peter W. Milonni & Joseph H. Eberly, “laser physics”, John Wiley &Sons, Inc,. Hoboken, New Jersey , 2010.
[3.] S. Y. Al-Dabagh, H. J. Kbashi, H. A. Hameed, “Implementation of optical coherent communication system
between two computers”, Baghdad Science Journal, Vol.7(1)pp( ) 2010.
[4.] Yash Jagdishlal Gawdi, “Underwater free space optics”, Master thesis, Raleigh, North Carolina, 2006.
[5.] Vikrant, Anjesh Kumar& R.S. Jha, “Comparison of Underwater Laser
Communication System with
Underwater Acoustic Sensor Network” , International Journal of Scientific & Engineering Research, Vol. 3,
Issue 10, October-2012.
[6.] LV Pei ,HE Junhua1 , Zhou Renkui1 , Liu Haiying, “The application of
underwater optics and its
development”, Information Optics and
Photonics Technologies II, Proc. of SPIE ,Vol. 6837, 68370I,
(2007) ·
[7.] Yingz Huang Liu, Xiaohu Ge, “Underwater Laser sensor network: A
New Approach for Broadband
Communication in the Underwater”,
Proceedings of the 5th WSEAS International Conference on
Telecommunications and Informatics, Istanbul, Turkey, May 27-29,
(pp421-425) , 2006
[8.] Ra´ul Palacios Trujillo, “Interference Cancellation and Network Coding
for Underwater Communication
Systems”, Department of
Telecommunication Technology, 10th Semester, Spring 2010.
[9.] Jared Scott Everett, “Forward-Error Correction Coding for Underwater
Free-Space Optical
Communication”, Master thesis, North Carolina 2009.
[10.] Thomas Scholz, “Using Laser Communication Above Water and
Underwater”, Compass Publications,
Inc., U.S.A., 2013 •
[11.] M. Ming and K. Liu “Principle and application of optical
communications”, Mc Grow – Hill companies,
1996.
[12.] B. Woodward &H. Sari “Underwater speech communication with a
modulated laser”, Appl. Phys. B 91,
pp.189-194 , 2008.
AUTHOR
Samar Y.Al-Dabagh received the B.Sc degree in Physics from Mosul University/Iraq in 1976, and
received M.Sc in physics from Northeastern University USA in 1986 and PhD in Physics from
University of Baghdad , Iraq in 2003 .She is a Assistant Professor at. at the University of Baghdad,
collage of science for Women , department of physics. Her current research interests include optical fiber
communication and laser nanotechnology.
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