A detailed numerical solution of the design criteria of in-phase lateral and single-longitudinal-mode operation GaInAsP/InP DFB laser arrays is presented. The analysis, including broad-area pumped and stripe-geometry pumped index-guided arrays, was carried out on the basis of the eigenvalue equation method. It is shown that there exists a cut-off array pitch co, at which all of the higher-order array modes are cut off. For the pitch larger than the cut-off pitch co, the modal discrimination is evaluated by the threshold gain difference between the in-phase lateral and higher-order array modes. As a result, the modal discrimination was found to decrease with the increase of the number of elements and the array pitch which is limited to be smaller than twice the cut-off pitch co to attain a stable in-phase lateral- and single-longitudinal-mode operation.

The basic properties of 1.55µm GaInAsP/InP distributed reflector (DR) laser were analyzed from the view points of active region structure and π/2 phase shift position. By introducing SCH structure with thin active layer, differential quantum efficiency could be improved up to 60-70% without sacrificing threshold current density. Optimum π/2 phase shift position for high power operation was found to be located inside the active region at a distance of 0.3 times of active region length from the joint portion between active and passive regions.