Two and three level optical PCM transmitter design for multigigabit systems using a relaxation oscillation technique

A theoretical method based on gain switching of semiconductor lasers is described which optimizes the bandwidth and modulated output power from a given laser for application in optical PCM systems. Both two- and three-level systems are considered. The type of laser used to demonstrate the technique is typical of an AlGaAs BH laser. A three-level optical system based on only two electrical drive levels is evaluated. Numerical results based on the single-mode rate equations, including a diffusion term, predict bit rates of 5 Gbit/s for a two-level system and 8 Gbit/s for the three level system. The technique was also applied to short cavity and quaternary lasers. For a short-cavity (100-μm) laser bit rates of 9 and 14 Gbit/s were predicted for the two- and three-level systems, respectively. For an In-GaAsP etched mesa BH laser bit rates of 10 and 16 Gbit/s were predicted for the two- and three-levels systems, respectively. The bandwidth was found to be limited by the laser parameters and catastrophic mirror damage which limits the maximum allowed drive current.