Linewidth Reduction of a 1.5 µm InGaAsP Laser by Electrical Feedback

Abstract

An electrical feedback technique was proposed for stable reduction of the spectral linewidth of a 1.5 µm InGaAsP laser (DFB type). By controlling the injection current with a servo control circuit of 0.5 kHz∼0.8 GHz bandwidth, the linewidth was reduced by more than five times that of the free running laser. The minimum value obtained here was 2 MHz. Attainable minimum value, which was limited by the shot noise of the detector, was estimated as being 1.0×10 -6 times that of the value given by the modified Schawlow-Townes formula.