Cavity designs for GHz frequency combs

A comprehensive modeling of the mode-locked laser is presented. The methodology, based for a large part on space-time analogy, applies to any cavity, but may be particularly important for short cavities with particular emphasis where very tight parameter control is essential. Unlike earlier models the beam deformation by nonlinear index in time and space is completely accounted for. It is shown that the mechanism responsible for starting mode-locking is not only Kerr lensing but also Kerr deflection. The problem of directionality in a ring laser is addressed. Will the operation be bidirectional, or unidirectional, and in the later case in which direction? It is suggested that this question can be addressed by considering the analogy between a ring laser and a quantum mechanical two level system. While it is generally taken for granted that multi-GHz combs can only be obtained by miniaturization of the laser, it is shown that a high frequency comb can be generated in a mode-locked laser by inserting a glass etalon.