Gain-lever lasers in optical subcarrier transmission systems

This thesis is concerned with the gain-lever effect in quantum well semiconductor lasers with a view to their application in subcarrier multiplexed fibre optical systems. The increased modulation efficiency and reduced noise figure of the gain-lever laser makes it very attractive for microwave optical transmission. However, their possible application to subcarrier multiplexed systems requires a full assessment of the effects of their intrinsic nonlinearity. With this in view, the first part of the study is dedicated to the modelling of the modulation and noise characteristics of the gain-lever laser based on the single-mode rate equations. These equations also provide an adequate basis for the analysis of the laser intrinsic dynamic nonlinearity. The Volterra series method of nonlinear system theory is then applied to develop analytical models that describe the nonlinear distortion. Both intensity and frequency modulation are useful in gain-lever laser transmitters. Therefore analytical models were developed that account for distortion effects of both the intensity and frequency components of the laser light as well as of a nonlinear optical discriminator. The Volterra theory enables the calculation of both the harmonic and intermodulation distortion power. This measure is used to compare different gain-lever laser transmitters to the conventional DFB laser. Finally, the analytic model is used to investigate both dynamic range constraints and the performance of a gain-lever laser transmitter in a fibre radio subcarrier multiplexed system