Analysis of bistability at the coupling between waveguide and whispering gallery modes of a nonlinear hemicylinder

The optical bistability caused by the coupling between modes of the parallel-plate waveguide and a nonlinear hemicylindrical crystal is studied using theoretical and numerical analysis. In such a system a waveguide channel is parallelly coupled to whispering gallery modes of a hemicylindrical microresonator ensuring bistable behaviour at input intensities of the order of a few MW/cm2. The characteristic minimum switching time of the system (around 30 ps) can be controlled by varying the thickness of the metal layer which couples the waveguide and whispering gallery modes. This is conditioned by the change of the quality Q-factor, as well as the coupling coefficient of the resonator. The main advantages of the system are fabrication simplicity, small sizes of the order of 3 µm and the possibility of adjusting the processes by making use of the electro-optical effect.