Silicon-based compact eight-channel wavelength and mode division (de)multiplexer for on-chip optical interconnects.

A compact wavelength and mode division (de)multiplexer is proposed for multiplexing a total of eight guided TE modes of a 220 nm thick silicon-on-insulator waveguide with input channels at two wavelengths of 1.55 and 2 µm for wavelength division multiplexing. The (de)multiplexer is composed of four sequentially arranged sections with bus waveguides of increasing widths. The first section uses an asymmetric directional coupler to couple one TE mode at 1.55 µm, while each of the next three sections consists of two collocated directional couplers to simultaneously couple two TE modes of the bus waveguide, one at each wavelength of 1.55 and 2 µm. Three linear adiabatic tapers are designed to connect the consecutive bus waveguides. The fundamental TE mode of the bus waveguide at 1.55 or 2 µm is coupled by using another adiabatic taper from a single-mode input waveguide. The simulation results show that over a broad bandwidth of >100n m the insertion loss and crosstalk for both wavelength bands is <1.15d B and <-27d B, respectively. In addition, a compact device footprint with a total coupling length of ∼61µm is achieved due to the use of collocated directional couplers in three sections.