IR-Absorption Sensor

In chemistry, the most versatile technique to characterize fluids regarding, e.g., the chemical composition is the infrared absorption spectroscopy. In order to obtain a single (hand-held) element, this thesis aims to develop a fully integrated IR-absorption sensor, which can be realized by utilizing an optical waveguide.

Numerical simulations have been implemented to investigate electromagnetic wave propagation in context of all involved elements of the sensor, in order to achieve a suitable design of the sensor. The numerical simulations cover the idealized dielectric slab waveguide as well as the utilized grating couplers, which are required to couple the IR-radiation between the ambiance and the waveguide. Due to the non-idealized waveguide geometry emerging from the fabrication process of the thin dielectric film and from the necessity of confining the measurement sample on a defined sensing area, the numerical simulation has been extended to take surface roughness and the present step transitions of the slab waveguide structure into account.

The experimental investigation of the waveguide structure was carried out by means of an FTIR-spectrometer and a measurement setup composed of commercial IR-elements to verify the theoretical results. Additionally, a lumped measurement setup was built up exploiting the system’s inherent spectral separation, which was successfully used to prove the functionality of the proposed concept.