Properties of Complex Coupled DFB Lasers Used as Narrowband Amplifiers

We have studied the properties of distributed feedback laser diodes with real and complex coupling used as narrowband optic amplifier. The implemented numerical model is based on the transfer matrix method and allows to analyze general multielectrode laser structures. This model takes into account the interaction between optical field and carrier population in the high input power regime, the thermal effect due to current injection, the spectral dependence of optical gain and the photon and carrier density dependence on the longitudinal coordinate. We report an example of application to the study of filter tunability. With regard to complex coupled DFB lasers (CC-DFB) we compare theoretical and experimental results for the spontaneous emission spectra. CC-DFB amplifiers show quite different nonlinear behavior in the high input power regime, depending on the relative phase between index and gain gratings. These results are related to the effective linewidth enhancement factor which depends, for these structures, on both the material and the grating characteristics.