Modulational instability in optical-microwave interaction

The mutual coupling of optical waves with microwaves in a medium with second order nonlinearity has attracted considerable attention At low optical powers the interaction is limited to the electrooptic effect which gives rise to a phase change in the optical wave proportional to an applied electric field. At high optical powers optical rectification, the generation of electrical signals from optical waves, can play a considerable role. The interplay between both effects has been shown to result in an effective cubic nonlinearity which can lead to self phase modulation and soliton formation. In this paper we consider the modulational instability (MI) of an optical continuous wave in a dispersive quadratic medium due to coupling to the rectified quasi DC-field. This process is similar to MI due to coupling between a fundamental and second harmonic