Side-mode suppression for long DBR lasers

We present the results of a traveling-wave analysis of the excitation of side longitudinal modes for a nearly-single mode DBR laser with long passive waveguide. The theory accounts for the intraband and interband mode mixing and predicts their joint multiplicative broadband effect on the side mode intensities. The sign of the effect depends on the location of the lasing mode on the net gain curve, yielding strong symmetrical side-mode suppression for negative frequency detuning. The spectrum thus features a symmetrical shape with asymmetrical tuning characteristics. The effect enables almost single-mode operation of cm-long DBR lasers.>