Unidirectional ring resonators for self-starting passively mode-locked lasers

Mode pulling and étalon effects have been claimed to prevent self-starting in passively mode-locked lasers that use fast saturable absorbers. A unidirectional ring geometry significantly reduces backscatter coupling and thus should facilitate self-starting. We present supportive evidence and demonstrate true self-starting in self-stabilized, passively mode-locked Ti:sapphire and erbium fiber lasers.