Wavelength Demultiplexer Designs Operating Over Multiple Spatial Modes of a Rectangular Waveguide

Wavelength demultiplexers are instrumental in wavelength division multiplexing (WDM) communications. In advance of space-division multiplexing (SDM) WDM communications, we investigate wavelength multiplexer/demultiplexer designs operating over multiplexed spatial modes simultaneously, when the modes are arranged along one transverse direction of a rectangular waveguide. The demultiplexer waveguides' modes match those of rectangular core fibers, enabling simple and efficient edge-coupling. We describe the challenge of demultiplexing mode division multiplexed (MDM) channels, and suggest guided optics solutions for its implementation. We analyze the spatial-spectral interplay at output waveguide coupling due to mode dependent phase delays in arrayed waveguide grating router demultiplexer design, and offer low mode dependent loss solutions. The proposed schemes allow for efficient and compact MDM-enabled WDM multiplexing, paving the way to SDM-WDM communication networks.