FSO not UFO
Laser technology is a fast growing market in last mile communication networks, but many still see it as a space age extravagance. Bela Gyeori reveals how free-space optics work and what laser systems have to offer.

Lasers have long been associated with Star Wars films and optical surgery. However, the popularity of this space age technology as a cost-effective solution for last mile communications is growing rapidly.

Over the next five years, the free-space optics (FSO) market is expected to grow to reach approximately $2 billion.

FSO is laser-driven, fibreless technology that supports high-bandwidth with no interference issues, licensing requirements or leased-line rental costs. It provides a reliable medium for for PABX, GSM base, LAN, campus and telephone network interconnections. Easy to install, FSO systems are a cheap (starting at about $3,000) and secure alternative to existing copper, fibre optic and wireless connections.

Reliable, fast and cost effective
Development in FSO technology has lead to the production of systems capable of transmitting signals at 1.5Mbps to 155Mbps (the equivalent to 2,000 simultaneous phone calls) with an availability of 99.9 to 99.999 per cent up to 5km. Laser links continue to operate in rain, fog, snow and even sandstorms (where previously transmission was simply lost).

For a range of applications, the reliability of FSO is much greater than that of rivals, including microwave and spread-spectrum radio. Installation of a laser network rarely takes longer than a day, maintenance is little more than an annual clean and change of location is no problem, making this solution cost-effective in the long term.

Range of uses
FSO networks are being utilised for a variety of applications:
  • Compusys is using FSO to run voice and VoIP telephony on a multi-building site.

  • A train operator in the South-East uses it to link to a new customer service centre on the opposite side of an electric railway line.

  • Axelero, Hungary's largest ISP, uses high-speed laser links as a last-mile solution to link to one of its biggest customers, a central Budapest University

  • A leading Formula One team use it to link garage and pits


Strong security
FSO transmission is a strong offering for those looking for a secure network connection, especially when compared to alternative wireless data connections. It is secure simply by its nature, as any attempt to intercept or 'trap the beam' during transmission between laserheads will cause a tapping device to trigger and the connection to be broken.

Location of the laserheads plays a key role in security. The majority of systems are placed on the roofs of buildings, taking the beam and equipment out of easy reach so that interception and sabotage are difficult.

An attempt to 'trap the beam' by aligning a bugging device would require a securely mounted structure, making the use of unstable hand-held devices impossible.

Unlike microwave or radio devices, FSO carries data in a straight narrow beam, making signal detection difficult.

Combating the weather
A long-standing issue in the growth and uptake of laser technologies is the adverse effect that weather can have on connections.

Molecular compounds of the air are changing continuously; humidity, fog, snow, rain and dust can appear in the optical path, resulting in a reduction in the strength of the beam, causing it to diffract or scatter.

Systems must therefore offer a significant power budget of more than 35dB, ensuring that data is transmitted, regardless of weather.

Laser safety
The transmission of lasers across the urban sky has raised issues regarding safety, particularly whether a laser link might cause harm to birds and other flying objects.

Excluding UFO (which are somewhat rare), birds larger than the receiver's optics may block the laser beam for a very short time. But the protocol running over the link, independent from the link operation, is designed to correct or repeat any corrupt or lost packet.

A range of international standards ensures full safety for users and those in the surrounding environment. The only additional safety consideration is to avoid looking directly at the beam.

Bela Gyeori is CEO at LaserBit Communications

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This was first published in May 2002

 

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