Integrated transversal equalizers in high-speed fiber-optic systems

Abstract—Intersymbol interference (ISI) caused by intermodal dispersion in multimode fibers is the major limiting factor in the achievable data rate or transmission distance in high-speed multi-mode fiber-optic links for local area networks applications. Com-pared with optical-domain and other electrical-domain dispersion compensation methods, equalization with transversal filters based on distributed circuit techniques presents a cost-effective and low-power solution. The design of integrated distributed transversal equalizers is described in detail with focus on delay lines and gain stages. This seven-tap distributed transversal equalizer prototype has been implemented in a commercial 0.18- m SiGe BiCMOS process for 10-Gb/s multimode fiber-optic links. A seven-tap dis-tributed transversal equalizer reduces the ISI of a 10-Gb/s signal after 800 m of 50- m multimode fiber from 5 to 1.38 dB, and im-proves the bit-error rate from about 10 5 to less than 10 12. Index Terms—Dispersion, distributed circuit, equalization, fiber-optic communications, transversal filter. I