Threshold gain difference requirements for nearly single-longitudinal-mode lasers

The probability of error for lightwave systems affected by mode partition fluctuations is related to laser parameters, laser bias and modulation currents, transmission bit rate, and encoding format (NRZ, RZ). A simulation-based solution of stochastic rate equations governing the laser dynamics is used to determine a probabilistic description of mode partitioning. The description is applicable to formula-based methods of evaluating the probability of error. A truncated-pulse-train Gauss-quadrature-rule method is used to accommodate many features unique to the problem of assessing the performance implications of mode partitioning. Extensive numerical results quantify, for several systems, the required threshold gain difference between the lasing mode and the dominant side mode. For example, for 2.4-Gb/s NRZ modulation, the threshold gain difference requirement increased from 3 cm^-1 to 7 cm^-1 as the bias current of the laser decreases from 1.1 to 0.9 times the threshold current