Theory of timing jitter in actively mode-locked lasers

An analysis of the pulse-to-pulse timing jitter in an actively mode-locked laser is presented. The model includes spontaneous emission noise, mode-locker driver phase noise, and cavity length detuning. Analytical expressions for the laser pulse train phase noise spectrum, the intensity power spectrum, and the rms timing jitter are given. The timing fluctuations are characterized by a time constant proportional to the cavity round-trip time times the number of locked modes squared divided by the modulation depth. The contribution from the modelocker driver phase noise will dominate unless high stability RF sources are used. The residual timing jitter due to spontaneous emission noise is very sensitive to cavity detuning. In most laser this can be reduced to subpicosecond levels by proper tuning of the cavity resonance frequency to the mode-locker driver frequency.