Four-Channel CWDM (de)Multiplexers Using Cascaded Multimode Waveguide Gratings

A silicon-based four-channel coarse wavelength- division multiplexing (CWDM) (de)multiplexer working in the O-band is proposed and realized. The present on-chip four-channel CWDM (de)multiplexer is composed of four cascaded optical filters with flat-top spectral responses, which are realized by combining a multimode waveguide grating (MWG) and a two-channel mode (de)multiplexer. For the realized flat-top CWDM (de)multiplexer with a ~18-nm channel-spacing, the measured 1-dB bandwidth is as large as 15 nm, which is ~75% of the channel spacing. The thermal sensitivity is also reduced from ~85 pm/°C to 46 pm/°C by introducing the compensation provided by an SU-8 upper-cladding with a negative thermo-optic coefficient.