Mirror external-cavity can modulate the spectrum of semiconductor lasers very strongly. But no study has been reported on the mirror external-cavity spectrum characteristics of the quantum-dot (QD) laser since it came forth. Based on self-made 1.5mm InAs/InP QD laser, its spectrum characteristics modulated by mirror external- cavity are studied. The periodicity, the multimode lasing and the mode change of the spectrum versus current are explained. Contrast to short coupling-cavity quantum-well lasers used for single mode, long cavity-length InAs/InP QD lasers show smaller mode-compression and much easier multimode-lasing under the modulation of mirror external-cavity.
