Coupled Optoelectronic Oscillation via Fundamental Mode-Locking in a Composite-Cavity Electro-Optic Microchip Laser

Composite-cavity electro-optic microchip lasers have been proposed as a source for high-speed, low-noise microwave and optical signals. Such signals can be produced from a single short-cavity laser using the coupled optoelectronic oscillation architecture, but strict control of the cavity longitudinal modes must be maintained to achieve fundamental mode-locking. The mechanism for this control is studied analytically and it is determined that the Lorentzian gain approximation does not predict nonadjacent modal effects in short-cavity lasers. A modification is presented which can explain these effects. Experimentally, the modal structure of an adjustable short-cavity laser is investigated and the results are consistent with the revised model. Finally, the results of the theory are used to design an optimized cavity geometry that is used to successfully demonstrate FM mode-locking and coupled optoelectronic oscillation at 20 GHz using a Nd:YVO₄/MgO:LiNbO₃ prototype.