25 Jun 2024

Gas detecting light source

MicroPhotons choice of instrument for gas detection and identification application was the AQ6377 OSA from Yokogawa

Optical systems specialist MicroPhotons reports it is using the highly accurate Yokogawa OSA to characterise a gas detecting light source.

One of the most effective tools in the fight against air pollution and carbon emissions is the technique of gas absorption spectrometry.

Used to detect gases such as carbon monoxide (CO), carbon dioxide (CO 2 ) and nitrogen oxide (NO), the technique is widely used in factories and processing plants, including semiconductor fabrication plants.

Gas absorption spectrometry takes advantage of the optical properties of gases in the Mid Wavelength Infra-Red (MWIR) wavelength band. Many gases of interest absorb light at a specific wavelength, with tuned lasers being a common light source – when compared to a reference medium, a gas of interest will absorb some of the laser light, and the detected optical power of the source will be reduced.

The value of the absorption peak allows the accurate detection and identification of a specific gas.

Based in Shanghai, MicroPhotons is a distributor of optical products as well as supporting its customers in the development of optical technology applications such as spectrometry and gas analysis and detection.

The company was approached by a customer to help it with a project that called for accurate measurement of optical systems in the MWIR portion of the spectrum.

MicroPhotons says the challenge was that existing technologies for detecting gas absorption rates require the use of liquid nitrogen to cool the emitters. MicroPhotons planned to replace the super-cooled emitters with a super-continuum light source, allowing gas absorption measurements to be performed at room temperature.

Although more convenient and saving a large amount of test time, this approach requires very high measurement accuracy in the optical spectrum analyser (OSA) used to characterise the light source.

Also, the gases to be monitored had absorption peaks at wavelengths across the whole MWIR spectrum, from 1.9 to 5.5 μm – most OSAs are designed for use in telecoms systems, which only require measurement of wavelengths up to 1.7 μm.

MicroPhotons says it was looking for a single instrument that could cover the entire MWIR spectrum. This could dramatically reduce test time and effort, avoiding the need to set up and calibrate more than one measurement instrument when testing equipment for the detection of gases with different absorption peaks.

To meet its customer’s needs, MicroPhotons chose the AQ6377 OSA from Yokogawa. Across the 1.9 to 5.5 μm range, the AQ6377 is reported to be the only OSA capable of analysing the entire wavelength spectrum.

The AQ6377 is the latest version of the Yokogawa AQ6300 series of OSAs. Said to be the world’s first OSA offering side mode analysis of MWIR lasers, it offers extended wavelength coverage into the MWIR region from 1.9 to 5.5 μm. Its long wavelength range makes the AQ6377 ideal for environmental sensing and medical applications.

The device also achieves wavelength measurement accuracy of ±0.5 nm and provides a close-in dynamic range of 50 dB, thanks to the sharp spectral characteristics of the AQ6377’s monochromator. This means that signals in close proximity can be clearly separated and accurately measured.

According to Mr Wang, CEO of MicroPhotons, the AQ6377 OSA has provided outstandingly accurate measurement of the emissions of both tunable lasers and the super-continuum light source. This accuracy was proved by a measurement exercise performed after characterisation of the super-continuum light source using the AQ6377.

Mr Wang says that MicroPhotons ran measurements of the absorption of emissions from the characterised super-continuum light source: “We measured the absorption spectra of a range of gases including C 2 H 2 , C 2 H 6 , C 3 H 8 , and NH 3 .

“The measurement results very closely tracked the data provided by the SpectraPlot online tool, which provides a reference for the optical characteristics of gases. This gave us great confidence that the measurement output from the AQ6377, on the basis of which we characterised the light source, is extremely accurate and repeatable over its very broad measurement bandwidth.’

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Company info: Yokogawa Europe