Athermal silicon nitride angled MMI wavelength division (de)multiplexers for the near-infrared

WDM components fabricated on the silicon-on-insulator platform have transmission characteristics that are sensitive to dimensional errors and temperature variations due to the high refractive index and thermo-optic coefficient of Si, respectively. We propose the use of NH₃-free SiN_x layers to fabricate athermal (de)multiplexers based on angled multimode interferometers (AMMI) in order to achieve good spectral responses with high tolerance to dimensional errors. With this approach we have shown that stoichiometric and N-rich SiN_x layers can be used to fabricate AMMIs with cross-talk <30dB, insertion loss <2.5dB, sensitivity to dimensional errors <120pm/nm, and wavelength shift <10pm/°C.