In this work, we demonstrate a cascaded ring resonator based wide stop-band filter. The filter consists of four cascaded rings and a bus waveguide. The first ring has a radius of 7 mu m, the second, third and the fourth rings have radius of 7.01 mu m, 7.02 mu m, and 7.03 mu m, respectively. The radius varion is designed for a small shift of resonant wavelength so that the combined resonance effect of four ring resonators exhibits a wide stop-band filter function compare to a single ring resonator. Both the bus and ring waveguides have a width of 480 nm. The thickness of the waveguides were 220 nm which is a standard silicon-on-insulator (SOI) wafer available in the market. A 100-nm gap is designed between the ring and the bus waveguide to provide optimum filtering. The device is fabricated using the American Institute for Manufacturing integrated Photonics (AIM Photonics) 300mm Multi-Project Wafer (MPW) service. It is tested using the AIM Photonics inline vertical grating coupled automated measurement tool with a tunable light source that has wavelengths ranging from 1485 nm to 1590 nm and a wavelength resolution of 60 pm. The fabricated cascaded ring filter exhibits a 3-dB stop-band about 6 nm wide with an extinction ratio of similar to 30 dB in across the S, C and L-bands. It is noted that the desired width of the stop-band is achievable by cascading required number of rings with slight radius variation.
