Study on distributed optic fiber gas sensors

Online detection of gas concentrations is important research topic recently. Based on the analysis of near infrared spectral absorption of acetylene, ammonia and carbon monoxide, a system using absorption type optic fiber for high sensitivity distributed detection of gases with wideband light source is demonstrated. Light source modulation harmonic measurement is presented in this paper. Wavelength modulation is realized by three modulated reflective fiber Bragg gratings and piezoelectric ceramics to obtain different narrowband output light. The three center wavelengths of fiber Bragg gratings' narrowband spectra are adapt to the absorption lines of acetylene, ammonia and carbon monoxide and in the region of the optical fiber' low-loss windows. The light is introduced by optic fiber to different gas cells with different gases for distributed detection. The high sensitivity detection of gases can be measured from the second harmonic signal. Each ratio of second harmonic signal and transmission signal is used to eliminate the disturbance of light source. Sensitivity is proved and cost is reduced. Visual instrument software Labview is used for programming.