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 Standard's Modal Bandwidth investigation group are reviewed to provide an understanding and to propose a solution to the bandwidth reduction observed in high-speed fiber optic test links based on laser transmitters and multimode fiber. The reduced bandwidth values, as compared to the manufacturers specified values, were caused by differential mode delay (DMD) in the optical signal. The cause of the DMD is linked to a combination of the launch conditions established between the laser source and multimode fiber. The criteria for developing a solution with the goal of modifying the launch conditions to eliminate DMD in laser transmission over 99% of multimode fibers are established. (C) 1998 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(98)00912-X].