Microring-resonator filters are fabricated by E-beam photolithography and inductive-coupled-plasma(ICP) etching technology.The cross-section size of the strip waveguides is 300 nm×320 nm,and the bending radius of the microring is 5 μm.The measured results show that the free spectral range(FSR) and extinction ratio(ER) at the wavelength of 1 550 nm are 16.8 nm and 18.1 dB,respectively.After thermo-optic modulation,the tunable filter wavelength range reaches 4.8 nm,and the tuning efficiency is 0.1...