25-08-2017, 09:32 PM
Free Space Optical Laser Communication Link
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INTRODUCTION
An initial hurdle faced by early means of laser communication
was the enormous heat generated by pumped laser action.
However, in the late 1960’s, semiconductor laser was developed
and ever since, the possibilities for laser communication have
grown. Though developed for carriers, new laser technologies are
finding a place in private networks [1][2]. Recent breakthroughs
in wireless technology and the need for a wireless extension of
the Internet have increased the demand for faster, higher
bandwidth wireless access networks [3][4]. The two wireless
options nowadays are either radio or optical networks. Radio
frequency has been the primary medium of communication for a
long period of time. However, in this day and age, the RF
spectrum has become congested and may no longer be sufficient
for broadband high-speed applications [5][6]. In addition to this
radio communication requires the leasing of frequencies in order
to be legally permitted to use them. On the other hand, optical
communication is the key to supply the ever-increasing demand
for higher bandwidth, without the associated hassles or
interference experienced with radio communication.
Entrepreneurs and technologists who know of this are borrowing
many of the technologies initially designed for fiber-optics
systems and applying them to what is now called Free Space
Optical (FSO) communication [7] as shown in Figure 1.
Figure 1: Basic overview of FSO communication
FSO systems run in the infrared (Ir) spectrum, which is at the
bottom of the light spectrum. Specifically, the optical signal is in
the range of 1 THz (1 TeraHertz = 1 trillion Hz =
1,000,000,000,000 cycles per second) in terms of wavelength.
FSO is a free space (wireless) technology, meaning that the
signal travels in the free space between transmitter and receiver,
rather than through a conductor such as a wire or fiber, or
through a waveguide of some sort. Another important feature of
FSO is that it is unaffected by electromagnetic interference and
radio frequency interference, which increasingly plague radiobased
communication systems [8]. FSO systems are used in
disaster recovery applications and for temporary connectivity
while cabled networks are being deployed [9].
A FREE SPACE OPTICAL LASER COMMUNICATION LINK
The free space optical laser communication link developed is
comprised of four circuits: the analogue transmitter and receiver,
the digital transceiver and the Voice Unit (VU) meter. This
combination of circuits will enable line-of-sight (LOS), fullduplex
voice and RS232-compatible data communication, over a
laser beam in free space.
System Overview
The completed system consists of two transceivers, each capable
of simultaneously transmitting and receiving either analogue or
digital information. The user has the option to manually select
between either analogue or digital information via means of two
switches, which control the laser transmitter and phototransistor
receiver. This translates to a system where, if necessary,
analogue information can travel in one direction while digital
information travels in the opposite direction. In normal operation,
the system is a full-duplex analogue/digital communicator.