broadband fibre

Sapphire fibre sensor could improve energy efficiency and enable cleaner air travel

Image credit: Dreamstime

A sensor made of sapphire fibre that can tolerate extreme temperatures has the potential improve energy efficiency and emission reduction in aerospace and power generation, researchers at Oxford University have said.

Each thread of industrially grown sapphire is less than half a millimetre thick but can withstand temperatures over 2000°C. When light is injected onto one end of the fibre, some of it is reflected back at a point along its length which has been modified to be sensitive to temperature. The wavelength (colour) of this reflected light is a measure of the temperature at that point.

Whilst the sapphire fibre seems very thin, in comparison to the wavelength of light it carries, it is huge. This means that the light can take many different paths along the sapphire fibre, which results in many different wavelengths being reflected at once.

The researchers overcame this problem by writing a channel along the length of the fibre, such that the light is contained within a tiny cross-section, one-hundredth of a millimetre in diameter. With this approach, they were able to make a sensor reflecting predominantly a single wavelength of light.

Sapphire optical fibre

Sapphire optical fibre

Image credit: Julian Fells/University of Oxford

The initial demonstration was on a short length of sapphire fibre 1cm long, but the researchers predict that lengths of up to several metres will be possible, with a number of separate sensors along this length.

This would enable temperature measurements to be made throughout a jet engine, for example. Using this data to adapt engine conditions in-flight has the potential to significantly reduce nitrogen oxide emissions and improve overall efficiency, reducing the environmental impact. The sapphire’s resistance to radiation also gives applications in the space and fusion power industries.

Research team member Dr Mohan Wang said: “The sensors are fabricated using a high-power laser with extremely short pulses, and a significant hurdle was preventing the sapphire from cracking during this process.”

Rob Skilton, head of research at RACE, UK Atomic Energy Authority, said: “These sapphire optical fibres will have many different potential applications within the extreme environments of a fusion energy powerplant.

“This technology has the potential to significantly increase the capabilities of future sensor and robotic maintenance systems in this sector.”

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