Asymmetrically coupled silicon-on-insulator microring resonators for compact add-drop multiplexers

We report on improved filter characteristics of microring resonators (MRs) used as add-drop multiplexers for integrated photonic circuits. By introducing an asymmetrical coupling of the signal waveguides to the resonator, a higher throughput attenuation and drop efficiency is attained. The throughput attenuation is the decisive property for the application of microrings in photonic networks since it determines the crosstalk between drop signal and add signal at the throughput channel of an add-drop multiplexer. Experimental results are compared with analytical relations. MRs with a free-spectral range of 24 nm are fabricated on silicon-on-insulator substrates. A crosstalk reduction by 8.8 dB due to asymmetrical coupling is demonstrated.