A slab waveguide sensor for a fully integrated IR-absorption sensor system - theoretical and experimental verification

Integrated IR-absorption sensors are attractive for various industrial applications, e.g., online condition monitoring of liquids such as lubrication oil. In this contribution, we present theoretical and experimental results showing that an appropriately designed waveguide represents a suitable absorption sensor element. 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 a single sensor element.