Abstract

Using bulk InGaAsP saturable absorbers, we passively mode lock a KCl:Tl color center laser in single- and coupled-cavity configurations near 1.55 μm, which is a wavelength range important for transmission and switching in fibers and spectroscopy of erbium-doped materials. We obtain in the single-cavity configuration pulses as short as 315 fs with high amplitude stability and ~65 mW average output power. By adding a partially transmitting mirror midway in the laser, we convert the laser to a coupled-cavity configuration and obtain 1.0–1.4 ps wide pulses at somewhat reduced pulse stabilities. Since the main cavity does not incur the absorber loss, the average output power now increases up to ~350 mW. Also, the coupling between the two cavities controls the effective cross-section of the saturable absorber. We compare directly these two principally different passive mode-locking techniques in terms of differing saturable absorption requirements and influence on the laser properties (self-starting conditions, pulse properties, and output power).

© 1992 Optical Society of America