Flat-passband silicon nitride cascaded Mach–Zehnder interferometer for coarse wavelength division multiplexing

We design and experimentally demonstrate a four-channel cascaded Mach–Zehnder interferometer (MZI) with flat-passband for coarse wavelength division multiplexing, based on a silicon nitride platform. The performance of MZI filters is closely related to the design of power splitters. By employing wavelength-insensitive bent directional couplers between each MZI for power distribution, the crosstalk among channels within the device can be minimized. Simulation results indicate that the center crosstalk of all four channels is less than −24 dB, with a 3-dB bandwidth of ∼20 nm. Measurement results show that the average crosstalk between adjacent channels is −16.5 dB. The 3-dB bandwidths of the four channels are ∼19.7, 19.3, 19.3, and 20.5 nm, respectively. Compared with conventional cascaded MZI devices using straight directional couplers, the bent DC-based device shows a clear advantage in crosstalk performance. This work is conducive to promoting the commercial application of such a device.