Abstract : Novel triangular resonators containing active and passive sections have been fabricated and characterised with various multimode-interference (MMI) lengths. The optimum MMI length and width turn out to be 108 and 9 mm, respectively. A free spectral range of approximately 228 GHz is observed near 1558 nm along with an on–off ratio of 9 dB. The proposed triangular resonator has the advantage of removing the direct coupling between the two access waveguides of the MMI coupler.