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We report an interferometer-assisted add-drop Sagnac ring that offers multi-channel transmission and independent programmability of extinction ratio, center wavelength, and bandwidth in a compact device. The fixed coupling section is replaced with a thermally tuned Mach–Zehnder interferometer (MZI), which enables continuous control of the effective coupling condition. The filter exhibits a free spectral range (FSR) of ∼0.270nm, with center-wavelength tuning over ∼50% of the FSR. Extinction ratios can be tuned from 8.8 to 21.1 dB, and the overall spectral window of the three-channel response can be continuously tuned from 0.180 to 0.240 nm via phase modulation. The complementary add-drop functionality of the proposed structure makes it a practical building block for scalable and reconfigurable multi-channel filtering and routing.
Li et al. (Fri,) studied this question.