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Optical chip senses multiple gases

18 Aug 2005

An optical integrated circuit promises high sensitivity detection of multiple gases at the same time.

Environmental monitoring and the analysis of food packaging could benefit from a new type of optical sensor that can detect the presence of several gases simultaneously. The device is the brainchild of KLOÉ, a 4-year old spin-off from the University of Montpellier in France.

At the heart of KLOÉ’s K-MZS sensor is a rectangular sol-gel chip that contains a series of laser-written waveguide Mach-Zehnder Interferometers (MZIs) -- one for each gas to be sensed and an additional reference for calibration purposes.

One arm of each interferometer passes straight through the chip, while the others feature an “active element” that is exposed to the atmosphere and contains an agent that reacts to the gas to be sensed.

When the target gas is present the refractive index of the active element changes, altering the signal at the output of the interferometer. Input and output optical fibers are connected to the chip in order to inject and collect light. The entire packaged device is about 5 cm long, 1 cm wide and 6 mm high.

According to Paul Coudray, the firm’s CEO, the measurements are very sensitive and almost instantaneous due to the close proximity between the waveguide core, active zone and the atmosphere. Something that is impossible to achieve with an optical fiber sensor.

“Presently we have made tests to detect oxygen using an active layer based on sol-gel doped with ruthenium, but the customer himself can deposit his own type of active element to suit another specific gas.” Coudray told Optics.org. “The big advantage is that we can integrate up to five or six sensors on the same chip.”

Other examples of potential active elements include palladium doped sol-gel for detecting hydrogen. KLOÉ is now trialling the sensors with customers and is exploring other potential applications such as biophotonics, food packaging and sensing hydrocarbon pollutants in water.

Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.

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