Analysis, design, and fabrication of GaAlAs/GaAs DFB lasers with modulated stripe width structure for complete single longitudinal mode oscillation

Complete single longitudinal mode operation of a Ga-AlAs/GaAs distributed feedback (DFB) laser has been accomplished by making use of a modulated stripe width (MSW) structure, which is characterized by its simple configuration and versatility, compared with the other equivalent schemes. After a brief explanation of its historical background, the coupled-mode equations are transformed into the characteristic equation for the DFB laser with arbitrary index modulation which has a form convenient for numerical analysis. Two specific examples of the stripe width modulation, that is, stepped and symmetric linear modulations, are then analyzed by making use of the equations. Optimum design of the stripe shape is subsequently carried out by assuming a particular waveguide structure. The effects of facet reflection on lasing characteristics are discussed to obtain the allowable limit of the reflectivity for effective functioning of the MSW. Calculation procedure and some results of their spectra below threshold are provided for the sake of subsequent examination of experimentally observed spectra