Relation between chirp and linewidth reduction in external Bragg reflector semiconductor lasers

A 1.5-μm single longitudinal mode semiconductor laser, formed by butt coupling an external Bragg reflector to a standard Fabry–Perot laser, is shown to have greatly reduced wavelength chirp and emission linewidth. The linewidth reduction is found to be proportional to the square of the chirp reduction, in agreement with a previous theoretical prediction. The linewidth and chirp reduction factor can be varied by changing the operating point of the laser. With a 3-mm-long Bragg reflector, a linewidth of 1 MHz at 5 mW has been achieved.