Spectroscopic Gas Detection Using Thin-film Mesoporous Waveguides

Chip integrated nanophotonic thin-film waveguides have received a lot of attention in recent years due to a focus on miniaturizing bulk-sized optical devices for mass deployment and low-cost tools [1] . Gas sensing based on thin-film waveguides through tunable diode laser absorption spectroscopy (TDLAS) is one such emerging application [2] . In a thin-film-waveguide-based gas sensor, the evanescent field of the guided mode is responsible for interacting with the gas molecules. However, in conventional waveguide designs, only a small fraction of the field exists in the evanescent field while the majority resides in the core of the waveguide material. This gives rise to poor interaction with the molecules. In order to address this issue, we propose a novel type of waveguide platform where the core of the waveguide is made of a mesoporous oxide film. This film consists of a network of interconnected pores of the order of few nanometres, which are large enough for the gas molecules to percolate the material and at the same time small enough not to induce light scattering adversely affecting the waveguide losses [3] . As the gas diffuses through the network of the pores, it interacts with the electric field that resides in the waveguide core, leading to enhanced gas detection sensitivity.