OFS, the fiber subsidiary of Furukawa Electric Co. Ltd., is accusing Alcatel SA (NYSE: ALA; Paris: CGEP:PA) of violating a patent pertaining to metro WDM transmission.

OFS announced yesterday it had filed the suit in U.S. District Court for the Western District of North Carolina (see OFS Sues Alcatel Over Fiber Patent).

The patent in question -- number 5,905,838 if you're keeping score at home -- was awarded in 1999 and covers a means of simultaneously transmitting Wavelength Division Multiplexing (WDM) signals in the 1550nm and 1310nm ranges. It pertains to OFS's TrueWave line of non-zero dispersion fiber.

According to OFS, Alcatel's TeraLight Metro and TeraLight Ultra fibers, introduced in 2001, make use of the patented technology (see Alcatel Announces Nouveaux Fibers). OFS began complaining to Alcatel in April of this year.

"We were not satisfied with the pace [of discussions with Alcatel], and it appeared we were just headed for an impasse," says OFS general counsel Ward Council. "They just disagree about the validity of our patent."

Alcatel officials declined comment.

In addition to requesting damages, the suit asks that Alcatel be barred from selling TeraLight Metro and TeraLight Ultra.

OFS's patent addresses the different dispersion problems incurred by 1550nm and 1310nm wavelengths. WDM transmissions in the 1550nm band can suffer from dispersion at high data rates, but this can be corrected with dispersion-shifting fiber.

The 1310nm band has the opposite problem: It exhibits zero dispersion on conventional fiber. That opens the door to a nonlinear effect called four-wave mixing, in which wavelengths can combine to form new, undesired wavelengths (see Chromatic Dispersion and Polarization Mode Dispersion (PMD) and Nonlinear Effects).

OFS claims its patent covers the creation of a dual-window fiber, one that shifts dispersion for 1550nm wavelengths but also presents an appropriate amount of negative dispersion for the 1310nm band.

— Craig Matsumoto, Senior Editor, Light Reading