Characterization of the optical-gain enhanced microwave-Q for a 20.97  GHz regeneratively mode-locked laser with a...

By treating a regeneratively mode-locked laser with a short ring length of 5.85 m as a coupled optoelectronic (OE) RF oscillator, the microwave quality factor (Q ) of its ring-cavity was characterized with the phase-shift approach. Specifically, the phase shift in the OE feedback loop of the mode-locked laser was varied, and the corresponding frequency shift in the photodetected first harmonic of its emitted pulse train was measured. An optical-gain enhanced Q of  ∼5.8×10⁴ was measured, which is an order of magnitude larger than the Q estimated for the same cavity before regenerative mode-locking. The experimental results were then compared with theoretical models developed to estimate the optical-gain enhanced Q of coupled OE oscillators.