Passive optical network (PON) is considered as the most appealing access network architecture in terms of cost-effectiveness,
bandwidth management flexibility, scalability and durability. And to further reduce the cost per
subscriber, a Fabry-Perot (FP) laser diode is preferred as the transmitter at the optical network units (ONUs) because of
its lower cost compared to distributed feedback (DFB) laser diode. However, the mode partition noise (MPN) associated
with the multi-longitudinal-mode FP laser diode becomes the limiting factor in the network. This paper studies the MPN
characteristics of the FP laser diode using the time-domain simulation of noise-driven multi-mode laser rate equation.
The probability density functions are calculated for each longitudinal mode. The paper focuses on the investigation of
the k-factor, which is a simple yet important measure of the noise power, but is usually taken as a fitted or assumed
value in the penalty calculations. In this paper, the sources of the k-factor are studied with simulation, including the
intrinsic source of the laser Langevin noise, and the extrinsic source of the bit pattern. The photon waveforms are shown
under four simulation conditions for regular or random bit pattern, and with or without Langevin noise. The k-factors
contributed by those sources are studied with a variety of bias current and modulation current. Simulation results are
illustrated in figures, and show that the contribution of Langevin noise to the k-factor is larger than that of the random bit
pattern, and is more dominant at lower bias current or higher modulation current.