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 <i>T</i><i>E</i>₁₁/<i>T</i><i>M</i>₁₁, <i>T</i><i>E</i>₂₁/<i>T</i><i>M</i>₂₁, and <i>T</i><i>E</i>₃₁/<i>T</i><i>M</i>₃₁ 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 (<i>I</i><i>L</i>)<5.59<i>d</i><i>B</i> and crosstalk (<i>C</i><i>T</i>)<-16.29<i>d</i><i>B</i> for all six modes at 1550 nm. Over the wavelength range of 1500-1600 nm, polarization-dependent loss (<i>P</i><i>D</i><i>L</i>)<0.94<i>d</i><i>B</i>, <i>I</i><i>L</i><9.33<i>d</i><i>B</i>, and <i>C</i><i>T</i><-11.84<i>d</i><i>B</i> can be obtained for all supported modes. The demonstrated phase-preset scheme can be applied to integrated waveguide devices for compact mode processing.