Effect of transmitter speed and receiver bandwidth on the eye margin performance of a 10-Gb/s optical fiber transmission system

We calculated the effect of the transmitter speed and receiver bandwidth on the electrical eye margin performance of a 10-Gb/s NRZ optical fiber transmission system. The transmitter under consideration used a 1.5 μm DFB-laser externally modulated by a zero-chirp LiNbO₃ modulator with NRZ, 2/sup 7/-1 PRBS data. The receiver was a pin-diode based direct detection receiver. Main results are (1) near optimum system performance is achieved when the 10-90% rise/fall-time of the transmitter output is 40 ps, only small improvement is obtained by using faster speeds and, (2) the optimum bandwidth of the receiver is at 10 GHz (the baudrate) for both the back-to-back and the 120-km transmission configuration. Thus, the optimum receiver bandwidth is at the baudrate (10 GHz) which is in conflict with accepted practice which suggests approximately 0.6× baudrate (6 GHz). The reason for this discrepancy is that we considered an optically amplified NRZ transmission system where the optical power level at the receiver input is well above the receiver sensitivity. Therefore, the impact of thermal noise is negligible and the system is dominated by ISI, which can be reduced by increasing the receiver bandwidth.