10-GHz ultralow-noise optical sampling stream from a semiconductor diode ring laser

We report, what is to our knowledge, the lowest-noise pulsetrain produced to date with an actively mode-locked external-cavity semiconductor diode laser. Operating characteristics at 10 GHz include dispersion-compensated pulsewidths as short as 1.2 ps, amplitude noise as low as 0.12% rms, and residual phase noise as low as 43-fs rms. Potential application of such a laser in a next-generation optical analog-to-digital converter would theoretically provide as much as 8.6 bits of resolution, while sampling a 5-GHz waveform at the Nyquist frequency.