Bandwidth enhancement of multimode fiber Gbits/s networks using conditioned launch

Summary form only given. There is currently much interest in high-speed LANs, with standards for gigabit Ethernet and fiber channel under development. The 62.5-/spl mu/m core multimode fiber (MMF), which is widely used for LANs, has minimum bandwidth specifications of 160 and 500 MHz/spl middot/km at wavelengths of 850 and 1300 nm, respectively. These values translate into link-length limitations of /spl sim/300 and 800 m, respectively, for the gigabit Ethernet rate of 1.25 Gbits/s. The over-filled launch (OFL) bandwidth, for which these values are specified is, however, not the worst-case bandwidth for all launch conditions. In particular, underfilled launches as obtained with current laser transceivers can reduce the link bandwidth to less than half the OFL value. This effect has led recently to specifications of the worst-case link lengths for gigabit Ethernet of 260 and 440 m for 62.5 /spl mu/m MMF operating at 850 and 1300 nm, respectively. This paper demonstrates that the link bandwidth can be restored using an offset launch scheme, so that link lengths of 800 m with gigabit Ethernet are possible. In this work, the effect of the use of laser-based transmitters in MMF links was studied using 13 different representative fiber samples, all of 62.5-/spl mu/m core diameter. Measurements have shown that in eight cases, the link bandwidth with a laser transmitter module is far below the bandwidth for the OFL. To study this effect, detailed impulse response measurements have been carried out with a launch from a single-mode fiber patch cord with variable radial position into the MMF.