Electronic equalization of polarization-mode dispersion in 40-Gb/s optical systems

Electronic equalization of polarization-mode dispersion (PMD) effects in 40-Gb/s optical systems is investigated through system-level analysis and integrated circuit (IC) design. A system-level analysis of first-order PMD effects is used to compare different electronic equalizer architectures as potential PMD compensators. It is found that a decision feedback equalizer (DFE) consisting of a 3-tap feedforward equalizer (FFE) and a 1-tap feedback equalizer (FBE) is able to increase the useful length of a PMD-limited optical system by more than eight times. Two modifications to the travelling-wave filter (TWF) topology are introduced which enable the decoupling of equalizer tap spacing and bandwidth. These new TWF topologies are used in the implementation of two 3-tap 40-Gb/s FFEs. The equalizer ICs are implemented in the TSMC 90-nm and 0.18-mum CMOS processes, and represent the first implementations of 40-Gb/s equalizers in CMOS.