We have used coherent photon seeding to reduce the noise in an actively mode-locked extended-cavity semiconductor laser. Feedback is provided by an auxiliary cavity terminated either by a wedge plate or by a phase-conjugate mirror. Both conventional and phase-conjugate feedback can reduce the low-frequency noise components (0–5 MHz) by as much as 36 dB, hence drastically reducing the pulse fluctuations. A noise reduction of as much as 18 dB is also observed in the 0.01–3.0-GHz frequency range. We obtained these results while preserving the pulse duration (26 ps) and improving the time–bandwidth product.
© 1998 Optical Society of America
(030.4280) Coherence and statistical optics : Noise in imaging systems
(030.5260) Coherence and statistical optics : Photon counting
(140.4050) Lasers and laser optics : Mode-locked lasers
(140.5960) Lasers and laser optics : Semiconductor lasers
Patrick Langlois, David Gay, Nathalie McCarthy, and Michel Piché, "Noise reduction in a mode-locked semiconductor laser by coherent photon seeding," Opt. Lett. 23, 114-116 (1998)