We experimentally investigate a gain-switched Fabry–Perot semiconductor laser externally injection seeded with a narrow linewidth continuous wave laser. We determine the dependence of pulse width, side-mode suppression ratio, and timing jitter on seeding power and seeding wavelength. As external seeding power is increased up to a certain value, we observe negligible change in pulse width, a linear increase in side-mode suppression ratio, and a linear decrease in timing jitter. Exceeding a certain value leads to substantial pulse broadening. By tuning the seeding wavelength across a chirped mode of the laser, we observe the lowest timing jitter and the largest side-mode suppression when the seed wavelength is aligned with the center of the chirped spectrum of a desired mode.
Unlike conventional hybrid mode-locking methods, a very low power (−1 dBm from a rf synthesizer) rf sinusoidal feeding signal is applied to the saturable absorber of the laser and ultrastable mode-locked pulse train at 34 GHz repetition rate is achieved. A new physical mechanism for the efficient hybrid mode locking is proposed.
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