980-nm External-Cavity Passively Mode-Locked Laser with Extremely Narrow RF Linewidth

摘要

This paper reports on the mode-locked operation of a 980-nm external-cavity passively mode-locked laser with extremely narrow RF linewidth. Optical pulses with 10-ps pulse duration were generated at a repetition rate of 955 MHz, with an average output power of 39.3 mW - which corresponds to a peak power of 4.1 W, generated directly from the oscillator. The RF spectrum displays a -3dB RF linewidth of only ~40 Hz, as well as a 60-dB dynamic contrast, revealing the exceptionally low-noise fundamental mode-locked operation of this laser. At a repetition rate of ~1 GHz, the highest peak power of 5.26 W was achieved, albeit with an increased -3dB RF linewidth of ~100 Hz. The two-section chip incorporated an active region with a dual InGaAs quantum well sandwiched by an asymmetrical waveguide, and was operated at room temperature. By taking advantage of the broad tunability of the repetition rate which external-cavity lasers can afford, we also investigated the limits of stable fundamental mode-locked operation at the lowest repetition rates (or maximum external cavity lengths).