Partnership runs Gigabit Ethernet over plastic fiber

By STEPHEN HARDY

A partnership among Asahi Glass Co. Ltd. (Tokyo), Mitsubishi Gas Chemical Co. Inc. (Tokyo), Keio University and XaQti Corp. (San Jose, CA) recently demonstrated the transmission of Gigabit Ethernet over graded-index plastic optical fiber. The transmission configuration, called Photonic Ethernet, takes advantage of waveguide star couplers based on polymer substrates. Proponents of the technology say it can be implemented for as little as $200 per port, which is similar to the cost of 10-Mbit/sec Ethernet networks.

Asahi provides the fiber, which is based on perfluorinated polymer rather than the polymethyl methacrylate material most commonly used in plastic fiber. The fiber has exhibited attenuation of approximately 0.3 dB/km at 1300-nm wavelengths, one-tenth of a decibel per kilometer more than silica fiber at the same transmission wavelength. The polymer fiber`s low modal dispersion characteristics enable it to accommodate higher bit rates than multimode glass fiber, according to the Photonic Ethernet team. The perfluorinated material also does not require the carbon-hydrogen bonding common to conventional acrylate polymers, and thus does not suffer from the flammability problems exhibited by these other materials. Much of the research conducted on these fibers occurred at Keio University.

Meanwhile, the polymer-based star couplers were developed at Mitsubishi. The couplers are manufactured using the selective photopolymerization technique and are currently available in 4- and 8-port configurations for wave splitting. The passive nature of the couplers enables the elimination of electronic switch or hub ports, thus lowering the cost of Gigabit Ethernet connections. They also can be combined with optical amplifiers to extend link lengths.

At the desktop, the architecture uses a Gigabit Ethernet adaptor optimized for plastic optical fiber. The adaptors use XaQti`s XMAC II media access controller chip, which supports both full-duplex and half-duplex "collision-based" Ethernet operation. Photonic Ethernet represents the latter method, running at half-duplex CSMA/CD (carrier sense multiple access with collision detection).

XaQti spokespersons claim that the company is the only firm to adapt its Gigabit Ethernet chips for use with plastic optical fiber. The company hopes that the advantages long touted by plastic-fiber proponents--low cost, ease of use, large core size, and greater bandwidth capacity than copper, among others--will help spur the deployment of Gigabit Ethernet to the desktop. q