Analysis of Laser Pulse Chirping in Mode-Locked Vertical-Cavity Surface-Emitting Lasers

Mode-locked vertical-cavity lasers have a large cross-sectional area and consequently a large saturation energy and large peak powers. We analyze excess optical bandwidth generation in these lasers and find that self-phase modulation due to optical pumping and gain saturation is the dominant factor in inducing laser pulse chirping. The large magnitude of the chirp makes intracavity prism-pair compensation difficult. Adjustment of the cavity length has a major impact on the pulse chirping, as observed experimentally. Proper adjustment can result in a large linear frequency chirp which can be compensated using external pulse compression techniques.