Semiconductor lasers are the most important light sources in optical communication systems.
Further improvements of performance and characteristics of the devices contribute to further
development of the communication systems. In this regard, two important physical properties
affecting performance of semiconductor lasers have been analyzed; namely the quantum noise
and optical feedback. The performance of semiconductor lasers, which is used in optical
communication systems, is theoretically investigated. Effects of nonlinear gain and
nonradiative recombination on characteristics of intensity and phase noises of lasers are
investigated. The results showed that both intensity and frequency noises around the
relaxation frequency are suppressed when counting the nonlinear gain in the rate equations [1].
An improved theoretical model to analyze dynamics, operation and noise of semiconductor
lasers under arbitrary strength of optical feedback ranging from very weak to very strong
optical feedback is presented [2]. A new set of modified rate equations of lasers operating
under optical feedback are proposed [2]. The simulation results showed that the operations of
semiconductor lasers are classified into continuous wave (CW), chaotic, and pulsing
operations depending on the operating conditions. The optical feedback noise is found to be
as low as the quantum noise level when the laser is injected well above its threshold level [3].