A 20-year-old problem is solved: a sapphire sensor is available that can withstand 1900°C

The authors of the work created a type of device called a fiber Bragg grating (FBG) sensor. His

can be used to controltemperature and voltage in optical communication systems. Typically, such devices are produced as silica optical fiber, but this design does not work at temperatures below 1000 °C.

FBGs made from sapphire fibers work more stable whenhigher temperatures - up to 1900 °C. Therefore, the devices can be used in extreme conditions, for example, to monitor gas turbines in jet engines. In addition, sapphire is resistant to radiation, so the sensor can be used in nuclear reactors and in space.

But there are also problems - these fibers are verythin and less than half a millimeter wide, but they are still much thicker than the wavelength of light. Therefore, the emitted light can be reflected internally at different wavelengths. Since, for example, the sensor uses a certain wavelength of reflected light to read the temperature, additional noise appears that distorts the signal.

In the manufacture of the device, scientists usedshort pulses of a powerful laser to avoid cracking the sapphire. Demonstration experiments were carried out on a piece of sapphire fiber 1 cm long, but the length of the fiber can be any, and not one, but several temperature-sensitive points can be placed on it.

These sapphire optical fibers can bebe used in different ways, for example in the extreme conditions of a fusion power plant. The technology could also potentially improve sensing and robotic technology to provide safe, low-carbon fusion power.

Rob Skilton, UK Atomic Energy Authority (AEA).

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