Measuring with electrical sensors is so… passe! The new kids on the block: optical sensors. These come in many forms, shapes and form factors, and are mostly derived from the telecom boom in the late nineties. There is more and more interest for this type of sensor, especially in the area of structural monitoring.
There are two groups of optical sensors: instrinsic and extrinsic. Intrinsic optical sensors change the property of light within the fiber itself, while extrinsic optical sensors change the property of light outside the fiber. An example of extrinsic optical sensor is a simple on/off light detector, which outputs a digital ‘1′ when there is light and a ‘0′ when light is not present. Extrinsic sensors are often used in security systems, toys and more.
Intrinsic optical sensors are not quite as common as extrinsic sensors. An example is Fiber Bragg grating (FBG) sensors. FBG sensors are created by “etching” periodic variation of refractive index to create a mirror that only reflects a certain frequency of light, or commonly known as color. As the fiber expands/contracts due to strain or temperature variations, the color reflected by the FBG changes.
The optical fiber with embedded sensors can be seen mounted on the wing.
Optical strain gauges are being evaluated and used by NASA, and you can see them mounted on an aircraft wing. They are also used by civil engineers in structural monitoring for buildings and bridges.
Engineers and scientists are now starting to see value in optical sensing and instead of adapting telecom technologies for sensing, are designing new innovative products and solutions tailored for measurement applications.
What are the advantages over electrical sensors you ask? It’s immune to corrosion, electro-magnetic inteference and lightning, it allows for many sensors on one single fiber, and requires no calibration. It’s a dream come true! – Nathan