Flat-Top CWDM (De)Multiplexer Based on MZI With Bent Directional Couplers

A low-crosstalk and flat-top 4-channel coarse wavelength-division multiplexing (de)multiplexer is proposed and demonstrated. The cascaded Mach-Zehnder interferometers are used to provide flat pass-bands. By utilizing the power splitters based on the bent directional couplers, the crosstalk of the Mach-Zehnder interferometers could be ultra-low for all four channels. The measurement results of the fabricated device show that the crosstalk is <;-20 dB over a 12-nm wavelength range, the 0.5-, 1-, and 3-dB bandwidths are ~13, ~16, and ~19 nm for all four channels, which agree well with the simulations. Furthermore, the device footprint can be as small as ~300 μm × 100 μm.