Silicon Dioxide Multi-Mode Interference Spectrometers

A multi-mode interferometer (MMI) spectrometer is a type of reconstructive micro-spectrometer based on imaging light propagation patterns in MMI waveguides. A waveguide scattering surface accentuates imaging light patterns in the multi-mode interferometer. This technology has been proven with an SU-8 core waveguide with an etched SU-8 nanograss scattering surface. This paper describes our creation of a fully silicon-based spectrometer using a silica core MMI waveguide. Scattering features were created in silica using SU-8 nanograss as an etch mask in a reactive ion etch (RIE). With optimized etch parameters, the silica core MMI spectrometer achieved an SNR of three with an incident light power of −68 dBm, which was almost 6 dB lower than designs with an SU-8 core.