TM-Mode coupling in magnetooptic waveguide caused by periodic perturbation

摘要

TM-modes coupling in an magnetooptic waveguide caused by periodic perturbation of the interface have been analysed. Introducing into waveguide structure a gyrotropic material give an additional "degree of freedom" namely external magnetic field. Using the coupled-mode theory the problem of mode interaction is reduced to pair of coupled equatios. Coupling between the modes propagating in the opposite direction is analyzed. When the appropriate phase matching condition (Bragg condition) is satisfied, the incident TM mode power decreases exponentially along the perturbation region. This evanescence behavior is result of the distributed "reflection" of incident power into the backward travelling TM mode. The evanescence behavior occurs for a range frequencies so called " forbidden" zone in which the propagation constan has an imaginary part. In magnetooptic waveguide the center frequency of the gap can be easy controlled by external magnetic field.