Extracted-clock power level monitoring scheme for automatic dispersion equalization in high-speed optical transmission systems

This paper proposes an automatic dispersion equalization system using extra cted clock power monitoring in order to facilitate the field installation o f high-speed time-division multiplexed (TDM) systems over existing fiber ca bles. The proposed scheme adjusts the dispersion of a variable-dispersion e qualizer so as to maximize the extracted clock power level. This scheme has a simple configuration, needs no communication channel between the transmi tter and the receiver, and is sensitive to parameters such as initial chirp ing and fiber input power. The clock power dependence on the fiber dispersi on is theoretically analyzed assuming that the return-to-zero (RZ) format i s used and that pulse broadening is small compared to the bit duration. We show that the clock power is maximized when the dispersion-induced waveform . distortion is minimized. Numerical simulations show that the proposed sch eme is effective with the non-return-to-zero (NRZ) format and for the case that the optimum total dispersion deviates from zero due to initial and/or self-phase modulation (SPM)-induced chirping. The operation of the proposed automatic equalization system is experimentally confirmed in 20-Gbit/s tra nsmission using both RZ and NRZ formats. Moreover, a 40-Gbit/s transmission experiment over 200km of dispersion-shifted fiber (DSF) is successfully de monstrated using the proposed equalization scheme.