Lasing characteristics of a mode-locked erbium-doped fiber laser using a laser diode as an optical modulator

Mode locking was achieved by inserting a high-speed direct modulation semiconductor laser in a cavity of a Er-doped fiber laser. When a laser diode was used as a saturable absorber, self-Q-switching and passive mode locking were observed. By using the laser diode in the gain region and directly modulating the laser diode, active mode locking from the fundamental order (3.96 MHz) to high orders was realized. The pulse duration decreased with increasing order. When the order was 390 (1.54244 GHz), the optical pulse duration was 120 ps. When a pulse current with a pulse width of about 100 ps was used for modulation, the pulse duration further decreased. When the order was 211 (834.21 MHz), the optical pulse was about 30 ps. When the polarization in the Er-doped fiber was controlled and was the same with the TE polarization of the laser diode, stable optical pulses were observed. (C) 1997 Scripta Technica, Inc.