Laser mode partition noise evaluation for optical fiber transmission

An evaluation of the influence of mode partition noise on error rate performance in a high bit rate optical fiber transmission system is presented. First, it is experimentally clarified that the intensity in each longitudinal mode of a laser diode fluctuates, although the intensity for the total mode is constant. It is also established that this fluctuation causes degradation of the error rate performance after transmission through a long optical fiber. The fluctuation is named 'mode partition noise.' Next a simple model for the fluctuation is proposed. The characteristics of the fluctuation are discussed on the basis of this model. Optical waveform fluctuation is found to be introduced by mode partition noise in the course of transmission through a long dispersive transmission medium. This optical waveform fluctuation and its frequency spectrum are calculated. Finally, the error rate performance is evaluated and specifications required for a laser spectrum to attain a given repeater spacing are clarified.