Optimum arrangement of high-order series-coupled microring resonator for crosstalk reduction

Series-coupling of microring resonators with different ring radii is effective for expanding the free spectral range,(FSR) to greater than 20 nm owing to the Vernier effect. In this study, we analyzed the dependence of the filter response of quadrupleseries-coupled microrings with two different ring radii on the arrangement of ring radii. As a result, it was found that an asymmetric arrangement can reduce crosstalk compared with symmetric and antisymmetric arrangements, and the physical reason for the,optimum arrangement was clarified. In addition, the dependence of adjacent channel crosstalk on the FSR expansion factor was analyzed.