Abstract : Rectangular microring resonators containing active and passive sections are fabricated and characterized with various multimode-interference (MMI) lengths. The optimum MMI length and width turn out to be 110 and 9 mm, respectively. The material platform and fabrication process used are the same used for other active and passive devices except for a deep etch step. Hence such resonators are easily integrated with other active and passive devices. A free spectral range of approximately 244 GHz is observed with an on–off ratio of 13 dB.