Tuning of Transmission Responses of an Optical Microring With Negligible Wavelength Shift

The tuning of transmission response of an optical microring resonator (MRR) always associates with significant shift of the resonant wavelength, which leads to serious problems for most of applications. In this letter, we demonstrate that the Mach-Zehnder-interferometer (MZI)-coupled microring resonators with asymmetric directional couplers in the MZIs could still have large magnitude and phase tuning range, while maintaining the resonant wavelength unchanged. An add-drop MZI-coupled microring resonator with asymmetric directional couplers is fabricated on a silicon-on-insulator chip, and the measurement agrees well with the theoretical prediction. Our study would be interesting to photonic integrated circuits, which require tunable MRRs.