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High-Rise Buildings Linked by Laser Beams

July 16, 1999

This compact transmitter-receiver sends megabytes of information through space in a zap.

A new networking system coming into use, called optical spatial communications, promises to join optical fiber and radio as a main pipeline sustaining the advanced information society. In the new system, laser beams are used to transmit large amounts of data at high speed from building to building. This laser networking, which might well be called the present-day version of communicating with beacons, boasts low cost and high speed.

Wireless Connection with Infrared Beams
The new system has been developed by a group of firms in the fields of networking and optical wireless communication equipment. The group recently set up an experimental network connecting six buildings in Tokyo's business district of Akasaka and has launched a trial service.

The system uses infrared lasers as its medium. Devices for transmission and reception are attached to the roofs or window frames of the buildings, which stand at distances of several hundred meters from one another. Placing the devices of two buildings so that they face each other enables high-speed data transmission on a par with fiber-optic networks.

One company involved in the experiment plans to use this system to deliver such data as computer graphics to the two television companies in its clientele. "Up to now we've been using CD-ROMs for the purpose, but with this system we should be able to send large-sized data instantly, at low cost, and without fail," comments a company representative hopefully.

Advantages over Optical Fiber
Because a semiconductor laser can emit intense radiation with a single crystal tinier than a grain of rice as its light source, its use has spread rapidly since the 1980s as a cornerstone of optoelectronics. Today it is widely applied for reading CDs (compact discs), MDs (minidiscs), and videodiscs, as well as for the input and output of other optical memory devices. Bar code readers used by supermarket cashiers also utilize this technology.

The new optical communication system uses a laser beam consisting of several parallel strands of light, which dilates only by one meter even after traveling a distance of two kilometers (1.2 miles) and thus transmits data with high efficiency. An automatic target-tracking device adjusts the direction of the beam to cover for blurring due to strong winds typical of high-rises. Moreover, unlike with radio waves, data transmitted with optical beams cannot easily be intercepted.

Another merit of this system is its low cost. Setting up a fiber-optic network with the same capacity costs over 100 million yen (8.3 million U.S. dollars at 120 yen to the dollar), including equipment purchasing and installation costs. With optical beams, however, no circuits need be laid, so the initial cost would be about one-tenth of that of optical fibers. Running costs would also be less than one half.

The downside of optical spatial communications, like the age-old beacon, is their vulnerability to natural phenomena that block light, such as heavy rain, fog, and snow. Experiments up to now have shown that data can be transmitted in pouring rain, but tests will be continued until March 2000 to further verify the system's reliability.

Many communication networks, both wired and wireless, are already in place in cities. With low cost and high transmission speed as its trump card, how big a share can optical beam networks grab in this urban communications market?

Trends in JapanEdited by Japan Echo Inc. based on domestic Japanese news sources. Articles presented here are offered for reference purposes and do not necessarily represent the policy or views of the Japanese Government.