In this paper, we present a quantitative near-infrared spectroscopy measurement of the chemical compositions of gas mixtures, such as natural gas, based on a photonic bandgap fiber gas cell. The absorption spectra of the methane and ethane gases were investigated in the near-infrared region. The absorption lines of the ethane gas were observed in the 1600-1616-nm region, and were totally different from those of the methane gas. To our knowledge, this is the first study to measure the individual absorption lines of ethane in this range of wavelengths, and our finding has a great potential for sensing highly sensitive gases.Index Terms-Gas measurement system, hollow-core photonic bandgap fiber, natural gas analysis, near-infrared region, optical spectroscopy.
A novel structure of a fiber-optic Fabry–Perot interferometric (FFPI) temperature sensor is presented in this paper. The design of the sensor is analyzed and evaluated by the finite-difference time-domain (FDTD) method. Then, the proposed sensor is fabricated using a conventional single-mode fiber (SMF). A gold (Au) layer and a nickel (Ni) layer are sputtered and electroplated on the surface of the SMF, respectively. As a Fabry–Perot (FP) cavity, a micro-punch-hole is machined by focused ion beam (FIB) milling. Here, the structure of the FP cavity can be considered a pair of bimetallic strips. On the basis of the sharp difference in thermal expansion coefficient between the fused silica and the metallic materials, the temperature sensitivity of the proposed sensor was determined to be over 70 pm/°C in the 0 to +60 °C range. The standard deviation of temperature is less than 0.15 °C in 1 h.
Silicon oxide (SiO x ) films grown by plasma-enhanced chemical-vapor deposition (PECVD) were investigated for applications in a course wavelength-division multiplexing (CWDM) network. The SiO x films were deposited on 4-in. silicon wafers based on the reaction of N 2 O/SiH 4 precursors. After postdeposition annealing at 1,150°C, the transmission spectra of the films prepared at different flow rates of the precursor were compared. We found that the transmission spectrum of the films deposited at the low-flow conditions can be flattened to a ripple of less than 0.5 dB ranging from visible up to 1,470 nm. In addition, the material losses at wavelengths around 1,500 nm caused by absorption of Si-H and N-H bonds were significantly reduced.
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