Parallel gas spectroscopy using mid-infrared supercontinuum from a single Si3N4 waveguide

Abstract

Efficient third-order nonlinear optical processes have been successfully integrated on silicon nitride (Si₃N₄) waveguides. In particular, owing to Si₃N₄ wide transparency window spanning from the visible to the middle-infrared (mid-IR), efficient mid-IR dispersive-wave (DW) generation from a fiber laser has been recently demonstrated, and its potential as a source for absorption spectroscopy of a single gas has been established. Here we show that the system can be further engineered to broaden the coverage of a single DW without losing efficiency, as to enable simultaneous and discrete detection of several gas-phase molecules within the 2900 and 3380cm^-1 functional group region. We demonstrate quantitative detection of acetylene, methane, and ethane using a simple direct-absorption spectroscopy scheme, achieving a several hundreds of parts-per-million noise-equivalent detection limit with a 5 cm long gas cell.