Compact Microring Resonator With 2 $,\times,$ 2 Tapered Multimode Interference Couplers

Compact microring resonator devices are realized by using a small SU-8 polymer strip waveguide that has an SU-8 polymer core (n ~ 1.573), an SiO₂ buffer (n ~ 1.445), and an air cladding. Due to the high index contrast of the optical waveguide, a small bending radius ( ~ 150 mum) is used for the MRR. To enhance the coupling between the access optical waveguides and the microring, 2 times 2 multimode interference couplers are used. The measured spectral response of the through port shows a high extinction ratio of over 15 dB and a 3-dB bandwidth of about 0.38 nm (corresponding to a moderate Q-value of ~ 4500).