Planar prism spectrometer based on adiabatically connected waveguiding slabs

• Our work is about a novel guided wave prism spectrometer.
• The work includes all modeling and design aspects of the proposed spectrometer.
• The spectrometer exploits the modal dispersion in slab waveguides.
• Slabs are connected adiabatically to prevent unwanted mode conversion and loss.
• The design strategy is illustrated by a numerical example assuming SiON technology.

The device principle of a prism-based on-chip spectrometer for TE polarization is introduced. The spectrometer exploits the modal dispersion in planar waveguides in a layout with slab regions having two different thicknesses of the guiding layer. The set-up uses parabolic mirrors, for the collimation of light of the input waveguide and focusing of the light to the receiver waveguides, which relies on total internal reflection at the interface between two such regions. These regions are connected adiabatically to prevent unwanted mode conversion and loss at the edges of the prism. The structure can be fabricated with two wet etching steps. The paper presents basic theory and a general approach for device optimization. The latter is illustrated with a numerical example assuming SiON technology.