Fabrication of digital planar holograms into high refractive index waveguide core for spectroscopy-on-chip applications

A novel class of large-bandwidth wavelength demultiplexers, based on digital planar holography for on-chip spectroscopy applications, was fabricated in high refractive index contrast SiO₂/Si₃N₄ planar waveguides. The devices consist of computer-generated digital planar holograms (DPHs) encoding the transfer function of the demultiplexers, engraved on the core layer of the optical waveguide. An optimized fabrication process has been developed to produce DPHs with an etching depth as low as 10 nm in Si₃N₄. The first spectrometer devices exhibit overall bandwidths as large as 98 nm and spectral channel spacings down to 0.3 nm/channel.