Measurement technique for methane concentration by wavelength scanning of a distributed-feedback laser

A new technique which takes advantage of distributed-feedback (DFB) laser wavelength scanning to measure methane concentration is presented. A wavelength scan of the methane absorption peak at 1665.9 nm is realized using sawtooth modulation of the current injected to a DFB laser. A reference methane gas cell is used to find the methane absorption peak around 1666 nm, and normalization is used to reduce outside influences such as power drift and fiber loss. The concentration is derived by arithmetic processing of the absorption coefficient of the methane gas. An application test is carried out in a coal mine and a long-term precision of 0.05% is achieved.