An intra-cavity absorption fiber gas sensor based on performanceenhanced techniques

The performance of an erbium-doped fiber ring laser based intra-cavity absorption gassensor was evaluated with performance enhanced techniques. A multi-line wavelength sweep techniqueand a weighted averaging technique were proposed for better gas detection. By selecting appropriatesystem parameters, 6 strong absorption lines near 1 530 nm of C2H2 were obtained with good spectrumresolution in one scanning period. One group with higher absorption coefficients was used for relativelylow gas concentration detection and the other with lower absorption coefficients was used for relativelyhigh gas concentration. Both the groups can be used for medium gas concentration detection. For variousconcentration cases, by choosing proper absorption lines and performing weighted averaging, detectionaccuracy can be obtained over an extended detection range. The minimum detection limit could be verylow after optimization.

Spectral Absorption Gas Sensor Based on Anti-Resonant Reflecting Optical Waveguide

An air-silica microstructure optical fiber based on the anti-resonant reflecting optical waveguide （ARROW） principle was used to develop a spectral absorption gas sensor. The ARROW fiber has an air core and an air cladding layer. An ARROW fiber with a length of 725mm was used to construct a sensing system to detect acetylene gas. The gas was injected into the fiber from one end of the fiber. The transmission spectra were collected using an optical spectrum analyzer. The results indicate that the system can detect the gas of different concentrations and has the good system linearity. The response time of the system is about 200 s.

Polarization-Insensitive Hybrid Plasmonic Waveguide Design for Evanescent Field Absorption Gas Sensor

We propose a polarization-insensitive design of a hybrid plasmonic waveguide(HPWG)optimized at the 3.392µm wavelength which corresponds to the absorption line of methane gas.The waveguide design is capable of providing high mode sensitivity(Smode)and evanescent field ratio(EFR)for both transverse electric(TE)and transverse magnetic(TM)hybrid modes.The modal analysis of the waveguide is performed via 2-dimension(2D)and 3-dimension(3D)finite element methods(FEMs).At optimized waveguide parameters,Smode and EFR of 0.94 and 0.704,can be obtained for the TE hybrid mode,respectively,whereas the TM hybrid mode can offer Smode and EFR of 0.86 and 0.67,respectively.The TE and TM hybrid modes power dissipation of~3 dB can be obtained for a 20-µm-long hybrid plasmonic waveguide at the 60%gas concentration.We believe that the highly sensitive waveguide scheme proposed in this work overcomes the limitation of the polarization controlled light and can be utilized in gas sensing applications.

Gas leakage monitoring with scanned-wavelength direct absorption spectroscopy

A natural gas leakage detector based on scanned-wavelength direct absorption spectroscopy is described. The sensor employs a multi-channel scanned-wavelength direct absorption strategy.It has the potential to simultaneously monitor methane and hydrogen sulfide in open path environment.Traditionally,scanned-wavelength direct absorption spectroscopy is the technique choice for natural gas leakage applications because of its simplicity,accuracy,and stability.We perform the gas sensor using direct-absorption wavelength scans with isolated features at 1-kHz repetition rate and the center wavelength is stabilized at the center of the 2v_3 band R（3） line of methane（1.65μm） and the（v_1＋v_2＋v_3） combination band of hydrogen sulfide（1.57μm）,respectively.The influence of light intensity fluctuations can be eliminated by using scanned-wavelength direct absorption spectroscopy.Because of the fast wavelength scanning,the sensor has a response time of less than 0.1 s.The sensor can be configured to sense leakages in path-integrated concentrations of,for example,100-ppm·m hydrogen sulfide and 10-ppm·m methane.

A new detection technique of gas concentration with optical spectrum absorption at near-IR wavelength

Wavelength modulation technique(WMT) and active intracavity technique(ACIT) are first introduced in this paper,which are used to realize the concentration detection of methane and acetylene respectively.When ACIT is combined with wavelength sweep technique(WST),the detection sensitivity of acetylene can be enhanced sharply.When ACIT is combined with WST and WMT,the detection sensitivity of acetylene can be enhanced further.