Design of coupled ring resonator CWDM multiplexers

In this work, we propose a new design for coupled ring resonator 1 times 4 and 1 times 8 CWDM multiplexers. The proposed design offers a sharp roll off factor of more than 0.75 and a crosstalk lower than -80 dB with acceptable insertion loss. Using SOI technology, the proposed structure results in 1 times 4 MUX with 130 times 130 mum² and 1 times 8 MUX with 90 times 150 mum² areas. The main disadvantage of the proposed design is the associated ripples in the passband that may approach 5 dB in some cases. This design could be considered as the limit of ring resonators in wide band filters.