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Common Misconceptions About Free Space Optics
by: Pablo Bandera
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.

Defining a Common Standard for Evaluating and Comparing Free-Space Optical Products
by: Pablo Bandera
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.

Optical Wireless: Low Cost, Broadband, Optical Access
by: Dr. David Rockwell & Dr. Stephen Mecherle
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.

Wavelength Selection for Optical Wireless Communications Systems
by: Dr. David Rockwell & Dr. Stephen Mecherle
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.

Environmental Qualification and Field Test Results for the SONAbeam™ 155 and 622
by: Robert T. Carlson and Slawomir Paciorek
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.

Compact Telescope for Free Space Communications
by: Vladimir Draganov and Daryl James
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.

Optical Gain & Lasers
Presentation by: Dr. David Rockwell