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Common
Misconceptions About Free Space Optics
by: Pablo Bandera
Abstract:
Although Optical Wireless or Free-Space Optics (FSO) has been in use
for decades by the military, only recently has it made its way into
the mainstream of broader markets. With this increased awareness come
a number of questions that are commonly raised. This paper seeks to
address these common concerns in order to facilitate learning about
the technology and its capabilities.
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Defining
a Common Standard for Evaluating and Comparing Free-Space Optical Products
by: Pablo Bandera
Abstract:
The fundamental concepts that describe how a Free-Space Optics (FSO)
link works are not too complicated. As usual, however, there is a difference
between theory and practice. It is one thing to describe an FSO system
on paper (or in a brochure), and quite another to have a robust and
reliable system working in the field. This basic problem is made worse
in this emerging market by various claims that are confusing or, quite
frankly, hard to believe. A parameter as straightforward as “output
power” may not be what you think. The key concept of “link
margin” is defined differently for different products. Understanding
some of the subtleties involved in achieving optimal performance will
help network builders and buyers of FSO products make intelligent decisions
about FSO, and can help differentiate product performance from product
hype.
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Optical
Wireless: Low Cost, Broadband, Optical Access
by: Dr.
David Rockwell & Dr. Stephen Mecherle
Abstract:
The global telecommunications network has seen massive expansion over
the last few years, catalyzed by the telecommunications deregulation
of 1996. First came the tremendous growth of the long-haul, wide-area
network (WAN), followed by a more recent emphasis on metropolitan area
networks (MANs). Meanwhile, local area networks (LANs) and gigabit ethernet
ports are being deployed with a comparable growth rate. In order for
this tremendous capacity to be exploited, and for the users to be able
to utilize the broad array of new services becoming available, network
designers must provide a flexible and cost-effective means for the users
to access the telecommunications network. Presently, however, most local
loop connections are limited to 1.5 Mbps (a T1 line). As a consequence,
there is a strong need for a high-bandwidth bridge (the “last mile”
or “first mile”) between the LANs and the MANs or WANs.
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Wavelength
Selection for Optical Wireless Communications Systems
by:
Dr. David Rockwell & Dr. Stephen Mecherle
Abstract:
This paper explores one of the most important trade issues, the selection
of the optical wavelength. Historically, most developers of such systems
have employed wavelengths in the near-visible infrared spectral region
(~ 780 nm to ~ 850 nm), principally because of the availability of efficient
and reliable direct semiconductor diode-based sources at those wavelengths,
and, for the 780 nm devices, the cost advantages of utilizing the same
wavelength as is used in CD recorders. While cost is obviously an important
factor in the wavelength trade, one must also consider several additional
constraints, most notably the need not to exceed eye-safe limits on
transmitted intensities under conditions of high data-rate transmissions
through heavy atmospheric attenuation (due to fog, for example). Other
important trade criteria include overall performance, and the potential
for system growth and scalability. When all of these factors are considered,
it becomes clear that a more judicious approach is to employ wavelengths
near 1550 nm, the same wavelength range used in commercial fiber-optic
communications networks.
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Environmental
Qualification and Field Test Results for the SONAbeam™ 155 and 622
by: Robert T. Carlson and Slawomir Paciorek
Abstract:
This paper discusses test methods and results of fSONA Communications
Corporation's SONAbeam™ 155-M, SONAbeam™ 622-M and SONAbeam™155-S systems
- free-space-optical data communication systems that use 1550 nm lasers.
Presented are results of environmental qualification tests and field
performance tests over link ranges of 450 meters and 5 kilometers. The
SONAbeam™ 155-M, SONAbeam™ 622-M and 155-S are three representatives
of a family of products that work in the range of 34-1250 Mbps. Very
robust performance is the emphasis in the design of these systems.
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Compact
Telescope for Free Space Communications
by: Vladimir
Draganov and Daryl James
Abstract:
Several types of telescopes are used for free space telecommunications.
The most common are Cassegrain and Gregorian telescopes. The main difference
between Cassegrain and Gregorian optical systems is that Gregorian telescopes
employ a concave secondary mirror located beyond the focus of the primary
mirror. This results in longer tube lengths, as the distance between
mirrors is slightly more than the sum of their focal lengths, which
is the reason Cassegrain systems are the most common. In addition, Gregorian
telescopes produce an upright image, while Cassegrain telescopes produce
an inverted image.
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Optical
Gain & Lasers
Presentation by: Dr. David Rockwell
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