Wideband silica mode (de)multiplexer based on an asymmetric multimode interference coupler with phase preset

A silica waveguide three-mode (de)multiplexer based on an asymmetric 3×3 multimode interference (MMI) coupler is demonstrated. The phase-preset scheme allows the (de)multiplexing of TE₁₁/TM₁₁, TE₂₁/TM₂₁, and TE₃₁/TM₃₁ modes with the compact MMI coupler. The three-dimensional finite-difference beam propagation method is adopted in design optimization. Ultraviolet photolithography and plasma etching have been adopted in device fabrication. The fabricated (de)multiplexer exhibits an insertion loss (IL)<5.59dB and crosstalk (CT)<-16.29dB for all six modes at 1550 nm. Over the wavelength range of 1500-1600 nm, polarization-dependent loss (PDL)<0.94dB, IL<9.33dB, and CT<-11.84dB can be obtained for all supported modes. The demonstrated phase-preset scheme can be applied to integrated waveguide devices for compact mode processing.