Design of a Novel Fully Integrated IR - Absorption Sensor System

Integrated IR-absorption sensors are required for various industrial applications, e.g., in online condition monitoring of liquids such as lubrication oil. The recent developments in micromachining technology enable the thermal insulation of adjacent system components and hence it is possible to integrate both, broadband infrared sources and detectors into a single system. In this contribution, we show that an appropriately designed waveguide structure represents an absorption sensor element yielding a sensitivity comparable to IR-transmission setups. To this end, we utilize the evanescent field of a single-mode waveguide with high sensitivity in the mid-infrared region, which is particularly interesting for a number of applications. Grating couplers are utilized for coupling broadband IR-radiation in and out of the waveguide, where the coupling angle can be used for spectral separation. This concept enables to integrate all components of an absorption sensor into one sensor element.