Abstract

Laser subharmonic signals generated through degenerate parametric oscillation exhibit interesting properties that may be used for optical signal phase stabilization and digital phase locking. The laser subharmonic generation may be described by a set of differential equations coupling the fundamental and subharmonic fields in a nonlinear medium with second-order susceptibilities. It is shown analytically that phase stabilization and bistability are possible for type 1 phase matching but not for type 2 phase matching or harmonic generation. Results of numerical integrations confirming analytical results are also presented. In normal pulsed optical parametric oscillation, the noise phase determines the mode of each pulse with equal probability. However, the ambiguity in-phase shift can be removed by an application of a seeding wave whose frequency is the same as that of the subharmonic. The seeding signal should be comfortably above the noise level but much weaker than the pumping wave. In addition, the seeding signal should be controlled to overlap the particular moment of creation of the subharmonic pulse. This concept leads to digital phase locking, and a design of an optical switch based on this principle is given in the literature.¹

© 1988 Optical Society of America