New sapphire fiber sensor enables cleaner energy and air travel

Researchers at the University of Oxford have developed a sapphire fiber sensor that tolerates very high temperatures and high radiation. The new sensor could be used in the harsh environment of nuclear fusion power generation and enable more streamlined air travel.

The advance is touted as a solution to a 20-year-old problem with existing sensors.

The research is based on fiber Bragg grating (FBG) sensors, widely used for remote voltage and temperature monitoring in optical communication systems.

They are usually in the form of silica optical fibers, but the operating temperature range of silica FBGs is limited to less than 1000°C.

For their work, the researchers used a sapphire optical fiber, which can withstand temperatures above 2,000°C.

In addition, it promises great long-term stability at higher temperatures. Therefore, this ultra-high temperature operation has potential for applications such as monitoring gas turbines in aircraft engines to enable significant efficiency improvements and emission reductions.

Sapphire is also radiation resistant, allowing measurements in nuclear reactors and preventing radiation dimming in space applications.

The sapphire fiber Bragg grating has its own problems.

Sapphire fiber looks very thin – less than half a millimeter thick – but compared to the wavelength of light, it is huge. This means that when light is injected into one end of the sapphire fiber, it can take many different paths along the fiber, causing many different wavelengths to be reflected simultaneously.

The researchers overcame this problem by inscribing a channel along the fiber with a femtosecond laser. In this way, the light is contained in a tiny section, one hundredth of a millimeter in diameter. Using this approach, they succeeded in making a sensor that primarily reflects a single wavelength of light.

In their first demonstrations, the sapphire fiber was about 1 cm long, but the researchers believe that lengths of up to several meters will be possible. This would allow temperature measurements to be made throughout a jet engine.

Using this data to tailor in-flight engine conditions has the potential to significantly reduce nitrogen oxide emissions and improve overall efficiency, thereby reducing environmental impact.

This is exciting news and another significant scientific achievement from our longstanding collaboration with the University of Oxford. This fundamental research could, over time, enable more efficient and accurate multi-point temperature measurement in harsh environments, improving control, efficiency and safety. We look forward to working with Oxford University to explore its potential.

Mark Jefferies, Rolls Royce

These sapphire optical fibers will have many different potential applications in the extreme environments of a fusion power plant. This technology has the potential to dramatically increase the capabilities of future sensor and robot maintenance systems in this sector, helping the UKAEA in its mission to provide safe, sustainable and low-carbon fusion power to the grid.

Rob Skilton, head of research at the UK Atomic Energy Authority.

More information: opg.optica.org

Going through www.ox.ac.uk

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