Microspectrometer with slab-waveguide transmission gratings.

An integrated transmission diffraction grating in a planar optical waveguide is presented for broadband spectroscopic analysis of liquids and gases. Silicon oxynitride slab waveguides on silicon substrates with low optical loss in the visible range are combined with a phase transmission grating exhibiting a blaze effect at 500 nm to achieve high-efficiency diffraction and high spectral dispersion. Collimated white light propagates through the waveguide and couples into air at a stepped formed planar grating. The beams of each adjacent step interfere constructively at the focal line of a cylindrical lens, its focal line positioned perpendicular to the waveguide plane. We used a common silicon photodiode array to detect the spectral data. Our approach is to develop a compact and economic spectrometer without moving parts that can be applied for UV-visible analysis and near-infrared industrial process control as well.