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 differ- ential 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.
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A 1998 study studied this question.