Optical filtering by microring resonators

We have numerically evaluated the filtering characteristics with two and three microrings of low Q values in a two-dimensional configuration. The filtering characteristics of the structure with two rings can be varied by changing the diameter of the rings and the distance between the rings, because the resonance characteristics vary with the diameter and the interference between the two sets of light passing through the two rings varies with the distance. The structure employed here can store the light energy not only in the two rings but also in the cavity containing the rings and the waveguides. By changing the size of one of the two rings, the filtering characteristics can be modified because of the change in resonance conditions for the two rings and the variation in the coupling strength between light in the waveguide and the ring. An additional ring and waveguide can be used to modify the filtering characteristics of the two-ring structure and for control in order to determine the desirable properties of filtering. The use of microrings sandwiched by waveguides leads to a decrease in the size, compared with the use of the current optical filters.