Michael D. Wheeler
Lucent Technologies has unveiled two types of optical fiber: one that promises increased bandwidth for local networks and another that features low dispersion for long-distance systems.
For metropolitan networks, the company developed AllWave, which provides 100 nm more bandwidth than conventional single-mode fiber. Its second fiber, TrueWave reduced slope, for long-distance networks, promises to decrease signal loss and increase capacity by up to 25 percent in dense wavelength division multiplexing (WDM) systems.
In designing its AllWave fiber, Lucent's engineers devised a method to eliminate the small amount of water that the glass retains during production. Water inhibits light from passing through certain regions, specifically in the 1400-nm band between 1350 and 1550 nm. Researchers devised a proprietary, ultrapurifying process that yields fiber that, they say, contains no detectable water molecules. Consequently, Lucent can use virtually the entire fiber spectrum, including the 1400-nm band.
"What that means is you have an optimal zone for high-speed transmission," said Janice Haber, systems engineering and technical marketing director for Lucent. "In [the 1400-nm] band, dispersion is much lower, much like nonzero-dispersion fiber."
She said the new fiber could accommodate a data rate of 10 Gb/s at two to three times the distance of conventional fiber at 1550 nm. Lucent is designing a multiterabit dense WDM system known as WaveStar All-Metro OLS to support AllWave's wider operating spectrum. The company recently tested 1400-nm lasers with the fiber, which will be available commercially in 1999.
To accommodate the demands for high-er capacities and higher speeds on future long-distance networks, the company developed glass fiber that allows transmission in the third and fourth optical windows.
The wavelength range known as the third window -- 1530 to 1565 nm -- is used by today's optically amplified dense WDM systems. Emerging systems will use the fourth window (1565 to 1620 nm) as well. Lucent says the TrueWave fiber optimizes performance in both wavelength ranges by reducing dispersion -- the property that causes signals to spread out and interfere with each other.
Haber said the fiber features 33 percent less dispersion than other nonzero-dispersion fibers and 55 percent less dispersion than large-area fibers, a mark that she says is close to ideal.