Compact planar 980/1550-nm wavelength multi/demultiplexer based on multimode interference

A compact integrated 980/1550-nm wavelength multi/demultiplexing coupler based on multimode interference effects is demonstrated. The device is useful for integration with rare-earth doped waveguide amplifiers and lasers. It is shown that the device performance can be optimized with an appropriate choice of the coupler width. The coupler is fabricated in a SiO₂-SiON deeply-etched rib waveguide system. Theoretical and experimental results for the demultiplexer configuration are presented. At an optimum coupler length of 458 μm, contrast of about 18 dB, and on-chip insertion loss of 0.5 dB at both wavelengths are achieved.