This paper examines Free Space Optics (FSO), a wireless transmission technology that uses laser or light pulses to transmit data through the air. Developed for military applications over two decades, FSO emerged as a commercially viable technology in 1999 and gained prominence following the September 11th attacks when FSO providers rapidly restored broadband links in New York City. The paper discusses FSO's technical specifications, including its line-of-sight architecture, operational frequency bands, and security advantages. It addresses the market drivers behind FSO adoption, particularly the cost and installation delays associated with traditional fiber optic local loops controlled by regional bell operating companies. The paper concludes with an overview of major FSO vendors and ongoing research initiatives, positioning FSO as a competitive alternative to conventional broadband infrastructure.
In November 2001, Smart Business Magazine published an article titled "Five Wireless Technologies to Bet Your Business On." Two of the technologies outlined were related to wireless networking in the personal area network (PAN) or local area network (LAN) space: Bluetooth and wireless fidelity (Wi-Fi). Two of the remaining three technologies were cellular telephony and data technologies operating in the 2.5G and 3G bandwidth spectrum. These four technologies were well established in the mainstream and had been growing at an enormous rate, so their inclusion was unsurprising. The final technology, however, was a relatively unknown wireless system called Free Space Optics (FSO).
FSO had been developed and used frequently by the U.S. military in situations ranging from ground-based battlefield communications to naval inter-ship secure communications. Despite nearly 20 years of military use, FSO remained commercially unknown until 1999, when the first of several companies began offering commercial versions in urban centers. Fast installation coupled with favorable price-to-performance characteristics helped FSO win contracts with the Smithsonian Institution, the Four Seasons Hotel in Seattle, Washington, and the New York Fire Department.
FSO received major industry recognition following the September 11th attacks in New York City. With the local Verizon central office incapacitated, FSO companies moved in and reestablished many high-speed broadband links within hours. The rapid deployment of these links, many with bandwidth in the hundreds of megabits per second (Mbps), brought visibility to a technology now viewed as one of the strongest competitors to the fixed local loop monopoly of regional bell operating companies (RBOCs). FSO is also positioned as a potential replacement for radio-based point-to-point and multipoint systems such as MMDS and LMDS in major cities.
Free Space Optics is known in some areas as wireless fiber or air-based fiber. Trade names for the technology include AirFiber, TeraBeam, and LightPointe. FSO uses laser or light pulses from laser diodes or light emitting diodes (LEDs) to send packetized data in the terahertz spectrum range. The two frequency bands commonly in use are the 780nm-900nm and the 1500nm-1600nm ranges. Most FSO vendors do not use the 1300nm band, also used in terrestrial fiber optics, because it has poor transmission characteristics through the atmosphere. These frequencies are the same spectrums used by land-based optical fiber systems, but with FSO the transmission medium is air itself rather than fiber.
Since the frequencies are optically based, an FCC assignment or license of spectrum is not required, as is the case with radio frequency (RF) systems. FSO is a line-of-sight technology typically used in point-to-point situations, although some multipoint versions are available. An FSO link uses a pair of optical transceivers aimed at each other for distances of up to 6 miles. FSO is a full-duplex medium providing balanced bandwidth across both paths. The optical transceivers can be placed on top of buildings or even behind building glass, offering flexible deployment options.
Since FSO is a line-of-sight technology, it lends itself well to security. The beam operates in wavelengths not visible to the naked eye, and the beam itself is very small—up to two feet in most cases—making it impossible to tap or intercept without bringing the beam down or causing noticeable performance degradation. The equipment required to tap the beam must be optical and contain mirroring equipment. Unlike RF or microwave line-of-sight systems, FSO does not create side lobes of RF radiation that can be picked up by rogue receivers.
A typical setup involves a point-to-point or point-to-multipoint link requiring bandwidths from T-1 to OC-12 (622 Mbps). The bandwidth can be tailored specifically per link, enabling service providers to manage bandwidth while protecting customers by having them procure and pay for only the bandwidth required. The medium operates at OSI Layer 1 transmission, meaning it can support proprietary transport protocols as well as Asynchronous Transfer Mode (ATM), Ethernet, and higher-level protocols. A benefit marketed by TeraBeam includes coupling voice services onto the link rather than requiring multiple connections for various services.
Each link is engineered at a main office and specifications are delivered to an installation technician. Installation in most cases takes just a few hours, with the bulk of time allocated to transceiver setup and installation. This contrasts sharply with optical fiber local loops, which have average lead times of 12 to 18 months.
The current market driver for FSO technology is the provisioning of specific high-speed bandwidths without the installation delays, bandwidth limitations, cost, or complications of the local loop. It has been estimated that nearly 90% of commercial buildings within the United States are within 2 miles of installed optical fiber backbones, but only 5% have actual fiber access. The problem is that access to the backbone fiber is often limited to copper-based connections to the RBOC central office, which in turn limit access speed. Alternatively, access to optical fiber requires a substantial outlay (typically $70 per foot) to lay optical fiber from the building to the installed backbone.
Monopolistic practices by the RBOCs and FCC tariff requirements place access fees for the local loop in the $800 to $3,000 per month range. With FSO, no local loop access fee is required. Payment for FSO service covers accessible bandwidth and transceiver rental only. Actual service fees are typically one-third to one-fifth the cost of carrier or satellite-based loops, making FSO an economically attractive alternative for businesses seeking high-speed connectivity without prohibitive infrastructure costs.
"Vendor expansion, DWDM integration, and adoption projections"
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