1,720,963 research outputs found
A novel optical fibre gas sensor employing pressure-modulation spectroscopy
No full textAn optical fibre gas sensor using a pressure-modulation resonant-acoustic reference cell is employed to pressure modulate technique is demonstrated. A the absorption of a gas in the near infra-red. The system exhibits good selectivity, low response to contaminant gases, and a noise-limited sensitivity equivalent to 50ppm by volume for methane sensing
Progress in fibre-remoted gas correlation spectrometry
No full textThe paper reports on the progress in gas sensing using real-time correlation spectroscopy, where a gas is used as a matched optical filter to recognize its own spectral absorption lines. The basic concept of correlation spectrometry involves the passage of light sequentially through two gas cells: a reference cell containing a known quantity of the gas to be detected. and a sampling cell where the presence of the gas is to be determined. An optical signal passing through both cells will suffer absorption due to the gas in each. If the absorption in the reference Cell is periodically modulated, then the total absorption depends on whether the gas absorption lines in the sampling cell correlate with those in the reference cell gas. Two methods of modulating the reference cell absorption are reported, pressure and Stark modulation. Results are presented for methane detection employing pressure modulation. The pressure fluctuations are generated within a compact resonant acoustic cell driven by a piezoelectric transducer. Also given are results for cross-sensitivity measurements with ethane as the contaminant gas. The Stark technique is applied to ammonia detection here, but can be used with many gases that exhibit a strong dipole moment
Correlation spectroscopy gas sensors compatible with fibre-optic remoted operation
No full textThe paper reports three basic methods of gas sensing using real-time correlation spectroscopy. In each method, a sample of the gas to be measured is used as a matched optical filter in order to recognise similar features in the absorption spectrum of gas in the measurement cell
Progress with optical gas sensors using correlation spectroscopy
Get PDFThe paper reviews recent progress on gas detection using real-time correlation spectroscopy. The general method relies on using a gas sample in a reference cell as a matched optical filter, to preferentially detect similar absorption spectra in a measurement cell. All variations of the method have the advantage of excellent selectivity for gases with narrow line spectra, even when using broadband sources for illumination. They are also suitable for remote detection over optical fibre leads. The recent progress is in two main areas. Firstly, the earlier reported Stark modulation method has been extended to investigate a novel hygrometer. Secondly, we have developed a novel multi-line light source, by combining a broadband optical source with a Michelson interferometer, where the latter contains a gas in one arm
Gas sensors using correlation spectroscopy compatible with fibre-optic operation
Get PDFThis paper reviews methods for gas detection using real-time correlation spectroscopy. These methods involve using a gas sample in a reference cell as a matched optical filter to detect, preferentially, similar absorption spectra in a measurement cell. The methods all have the advantage of excellent selectivity, even using broadband sources, and are suitable for remote detection over optical-fibre leads. Our previously published methods using pressure and Stark modulation are reviewed. In addition, our recent theoretical treatment of the methods is presented. Finally, we describe new atmospheric-pressure measurements of gases using the method of phase-modulation spectroscopy
Elimination of excess photon noise from fibre super-radiant sources
No full textHigh-power incoherent sources such as ELEDs and rare-earth-doped superfluorescence sources exhibit excess photon noise which limits their application in sensors such as the fibre-optic gyro. We show that this form of noise can be eliminated by a compensation scheme
Broadband sources for gas detection using fluorescent rare-earth-doped fibres pumped by low-cost semiconductor laser source
No full textThe paper discusses recent results on sources for gas detection using fluorescent rare-earth-doped optical fibres. The sources are being optimised for use with broadband cognitive gas sensors, in particular those using correlation spectroscopy, with the constraint of using low-cost semiconductor lasers as the pump
Simple lead insensitive heterodyne fibre-optic vibrometer having a passive all-glass instrument head
No full textA novel fibre-optic laser vibrometer has been developed in which a single highly birefringent fibre links the launch optics with a simple passive all-glass instrument head. The instrument utilises heterodyne detection and can be made insensitive to undesired vibration effects acting on the fibre. The instrument may be greatly simplified and its performance enhanced if it is realised in all-fibre form
Tunable fibre laser source for methane detection at 1.68µm
No full textA tunable fibre laser for spectroscopic gas detection is reported for the first time. The laser is based on a single-mode thulium doped fibre, which can operate at a wavelength around 1.684µm, corresponding to a significant absorption line for methane. The fibre laser was pumped at 786nm, a wavelength which is readily available with AlGaAs laser diodes and an optical threshold power of 43mW was observed. An in-fibre photorefractive grating was used as the wavelength-selective output coupler for the laser. Simultaneous straining and heating of the grating induced a change in lasing wavelength, and a tuning range of up to 2nm was demonstrated. This new tunable light source was configured within a methane detector and absorption spectra were recorded which demonstrate the presence of this gas. The large tuning range of the thulium fibre laser should allow the detection of many gas species with absorption bands in the wavelength region 1.65µm to 2.05µm
- …
