Mid-infrared sensing waveguides embedded in silica glass: Detection of water phase and ice microstructure in harsh-environments

The development of mid-infrared (l~3-20 mm) integrated optical sensors has accelerated within the last years. The main driving interest is the potential of using photonic integrated elements capable of direct interaction with biomolecules and chemicals through their ground molecular vibrational modes, so that resonance fingerprints are exploited for novel sensor industrial applications. State-of-the-art ultrahigh-sensitivity photonic sensing schemes rely on exposing the evanescent field of tightly confined light to the environment. Yet these devices are extremely fragile, and any surface modification or damage entails irreversible sensor malfunction. Since adding a protective layer disables these sensors, there exists a technology gap for highly-sensitive harsh-environment resistant surface photonic sensors. Here we propose the use of mid-infrared waveguide sensors which exploit vibrational resonance-driven directional coupling effects besides absorption, so that waveguide sensing elements can be buried (~1-10 mm) and resist systematic exposure to industrial environments without failure.