Actively Mode-Locked Semiconductor Laser with Feedback at an Intermode Frequency

This is a study of an active mode synchronization regime (mode locking) in a three-mirror semiconductor laser obtained by modulation of the laser current at the frequency of intermode beating of the external laser cavity through a feedback circuit. Under certain conditions stable active mode-locking is observed, and when the length of the external cavity is varied, corresponding tuning of the intermode beat frequency occurs. The main conditions under which this regime is attained are determined. The width of the intermode beating spectrum is found experimentally to be ~300 Hz for an intermode frequency of 300 MHz. The half width of the optical spectrum is ~4 nm.