Bandwidth reduction in gigabit ethernet transmission over multimode fiber and recovery through laser transmitter mode conditioning

The experimental work carried out by members of the Gigabit Ethernet Standa rd's Modal Bandwidth investigation group are reviewed to provide an underst anding and to propose a solution to the bandwidth reduction observed in hig h-speed fiber optic test links based on laser transmitters and multimode fi ber. The reduced bandwidth values, as compared to the manufacturers specifi ed values, were caused by differential mode delay (DMD) in the optical sign al. The cause of the DMD is linked to a combination of the launch condition s established between the laser source and multimode fiber. The criteria fo r developing a solution with the goal of modifying the launch conditions to eliminate DMD in laser transmission over 99% of multimode fibers are estab lished. (C) 1998 Society of Photo-Optical Instrumentation Engineers. [S0091 -3286(98)00912-X].