Sensing technology has been widely investigated and utilized for gas detection. Due to the different applicability and inherent limitations of different gas sensing technologies, researchers have been working on different scenarios with enhanced gas sensor calibration. This paper reviews the descriptions, evaluation, comparison and recent developments in existing gas sensing technologies. A classification of sensing technologies is given, based on the variation of electrical and other properties. Detailed introduction to sensing methods based on electrical variation is discussed through further classification according to sensing materials, including metal oxide semiconductors, polymers, carbon nanotubes, and moisture absorbing materials. Methods based on other kinds of variations such as optical, calorimetric, acoustic and gas-chromatographic, are presented in a general way. Several suggestions related to future development are also discussed. Furthermore, this paper focuses on sensitivity and selectivity for performance indicators to compare different sensing technologies, analyzes the factors that influence these two indicators, and lists several corresponding improved approaches.

A Survey on Gas Sensing Technology

An objective analysis is carried out of the matricial models representing the polarimetric properties of light and material media leading to the identification and definition of their corresponding physical quantities, using the concept of the coherency matrix. For light, cases of homogeneous and inhomogeneous wavefront are analyzed, and a model for 3D polarimetric purity is constructed. For linear passive material media, a general model is developed on the basis that any physically realizable linear transformation of Stokes vectors is equivalent to an ensemble average of passive, deterministic nondepolarizing transformations. Through this framework, the relevant physical quantities, including indices of polarimetric purity, are identified and decoupled. Some decompositions of the whole system into a set of well-defined components are considered, as well as techniques for isolating the unknown components by means of new procedures for subtracting coherency matrices. These results and methods constitute a powerful tool for analyzing and exploiting experimental and industrial polarimetry. Some particular application examples are indicated.

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Polarimetric characterization of light and media - Physical quantities involved in polarimetric phenomena

Environmental effects on nanogenerators

The present invention provides novel apparatus and methods for fast quantitative measurement of perturbation of optical fields transmitted, reflected and/or scattered along a length of an optical fibre. The present invention can be used for point sensors as well as distributed sensors or the combination of both. In particular this technique can be applied to distributed sensors while extending dramatically the speed and sensitivity to allow the detection of acoustic perturbations anywhere along a length of an optical fibre while achieving fine spatial resolution. The present invention offers unique advantages in a broad range of acoustic sensing and imaging applications. Typical uses are for monitoring oil and gas wells such as for distributed flow metering and/or imaging, seismic imaging, monitoring long cables and pipelines, imaging within large vessel as well as for security applications.

Method and apparatus for optical sensing

Influence of birefringence dispersion on a distributed stress sensor using birefringent optical fiber

Wavelength modulation technique (WMT) and wavelength sweep technique (WST) are introduced into intracavity fiber laser for both gas concentration sensing and absorption wavelength detection in this paper. The principle of gas sensing and spectral analysis using WMT and WST was studied. Polynomial fit was adopted to model the system nonlinear characteristic, based on which absorption wavelength can be detected. The system optimization and acetylene gas sensing were both realized, and the absolute detected error can be increased less than 75 ppm. The absorption wavelengths of the detected gas were calculated based on the polynomial fitting results of the system nonlinear. The absorption wavelengths of acetylene were detected using this method, with absolute error no more than 0.445 nm. The system has the ability of realizing both concentration sensing and gas-type recognition.

Investigation of Wavelength Modulation and Wavelength Sweep Techniques in Intracavity Fiber Laser for Gas Detection

A new method for measuring the birefringence dispersion in polarization-maintaining fibers (PMFs) with high sensitivity and accuracy is presented. The method employs white-light interferences between two orthogonally polarized modes of PMFs. The group birefringence of the fiber is calibrated first. Then the birefringence dispersion and its variation along different fiber sections are acquired by analyzing the broadening of interferograms at different fiber lengths. The main sources of error are investigated. Birefringence dispersions of two PANDA fibers at their operation wavelength are measured to be 0.011 ps/(km nm) and 0.018 ps/(km nm). A measurement repeatability of 0.001 ps/(km nm) is achieved.

Characterization of birefringence dispersion in polarization-maintaining fibers by use of white-light interferometry.

A new method to measure the birefringence dispersion in high-birefringence polarization-maintaining fibers is presented using white-light interferometry. By analyzing broadening of low-coherence interferograms obtained in a scanning Michelson interferometer, the birefringence dispersion and its variation along different fiber sections are acquired with high sensitivity and accuracy. Birefringence dispersions of two PANDA fibers at their operation wavelength are measured to be 0.011 ps/(km nm) and 0.018 ps/(km nm), respectively. Distributed measurement capability of the method is also verified experimentally.

Distributed measurement of birefringence dispersion in polarization-maintaining fibers

A broadband optical rotary joint (BORJ) was designed using C-lenses. Its insertion loss was less than 2 dB at both the 1300 nm and 1550 nm wavelength windows. Wavelength division multiplexing (WDM) technique was adopted to increase the number of data transmission channels. Hundreds of wavelength channels can be accommodated for data transmission through relatively rotating interfaces using this BORJ. The total data transmission rate through this BORJ can be more than 200 Gbit/s. By using Dove prism, both space division multiplexing (SDM) and WDM techniques can be implemented simultaneously in the design of BORJ with C-lenses. This structure of BORJ has a low cost. It can be used for optical data transmission and optical sensing.

Wencai Jing

Papers

Influence of birefringence dispersion on a distributed stress sensor using birefringent optical fiber

Investigation of Wavelength Modulation and Wavelength Sweep Techniques in Intracavity Fiber Laser for Gas Detection

Characterization of birefringence dispersion in polarization-maintaining fibers by use of white-light interferometry.

Distributed measurement of birefringence dispersion in polarization-maintaining fibers

Design and implementation of a broadband optical rotary joint using C-lenses