Selffocussing phase transmission grating for an integrated optical microspectrometer

An integrated optical microspectrometer in slab waveguides is presented for broadband spectroscopy in the visible wavelength range. Monomode silicon oxinitride (SiON) waveguides on silicon substrates are structured to produce a novel selffocussing waveguide transmission grating with a waveguide to air index transition endface. Regarding reflection gratings such transmission gratings have four-times larger facettes which is linked to reliable fabrication by standard thin film technology as well as to an exceptional high spectral dispersion. Combined with further functional optic elements, a compact microspectrometer is presented for long-term stable operation. The selffocussing and dispersion properties of the transmission grating are developed theoretically by phase matching and evaluated successively with electromagnetic theory. The spectral and spacial condition of constructive interference is generated in the waveguide plane at a focus length of only 13 mm yielding a miniaturized,: integrated optical, chirped 'grism' - grating prism - a specially designed planar imaging optic with structured waveguide endfaces results in a compact and monolithical core. The fabrication sequence based on standard thin film technology consists of a single deposition and etching process which allows an economic manufacturing. The realized microspectrometer exhibits high efficiency >60% in the first diffraction order and a spectral range of 350-650 nm with a spectral resolution of 9 nm. (C) 2001 Elsevier Science B.V. All rights reserved.