THEORY OF COUPLED-CAVITY MODE-LOCKING WITH A RESONANT NONLINEARITY

Recently, mode locking of a Ti:sapphire laser with a quantum-well reflector in an external cavity was reported [Opt. Lett. 15, 1377 (1990)]. This laser was found to operate with a stable mode-locked pulse train without stabilization of the external cavity. We develop a theory that shows that the system operates by small frequency adjustments. The laser continuously seeks the carrier frequency, which ensures coherent superposition of the pulses at the coupling mirror. Coupled-cavity resonant passive mode locking, as this new mode-locking mechanism has been called, is a form of self-stabilized coupled-cavity mode locking with a resonant nonlinearity. We show that self-stabilizing operation cannot be realized with a Kerr medium (reactive nonlinearity) in the cavity.