Design of CWDM multiplexers based on series coupled ring resonators: analysis, potential and prospects on MEMS fabrication technologies

New designs for a 1 x 4 and a 1 x 8 CWDM multiplexers based on cascaded groups of series coupled ring resonators (Little et al. in J Lightwave Technol 15:998-1005, 1997; IEEE Photon Technol Lett 10:2263-2265, 2004; Hryniewicz et al. in IEEE Photon Technol Lett 12:320-322, 2000) are presented. Compared to other integrated optical alternatives such as MMI phasars (Paiam and MacDonald in Appl Opt 36: 5097-5108, 1997), cascaded Mach-Zehnder interferometers (Wang and He in J Lightwave Technol 23:1284-1290, 2005) and cascaded AWG (Dragone in IEEE Photon Technol Lett 3:812-815, 1991; Uetsuka in IEEE J Sel Top Quant Electron 10:393-402, 2004), the proposed circuits offer superior performance in their very sharp roll-off factor that exceeds 0.75, their reduced crosstalk level that lies below -60 dB and their negligible insertion loss for the 1 x 4 design. For the 1 x 8 design, the worst case insertion loss is 4 dB. However, the performances obtained exhibit passband ripples in the order of 5 dB, and besides, they are not very tolerant to fabrication errors. Being designed for SOI technology, the proposed circuits are compact as the circuit areas are 130 x 130 and 90 x 150 mu m(2) for the 1 x 4 and 1 x 8 designs, respectively. They also have a high potential for MEMS tunability.