Optical fiber sensors

Summary

We have studied in this chapter the most significant techniques using intensity modulation optical fiber sensors. Here is a summary of the characteristics of the different transducers:

The sensors going by microbenders

They are intrinsic sensors (i.e. they modulate light intensity without making it going out of the fiber), they are particularly suited for measuring displacements. Because of their principle they are very sensitive and they have a big amplitude of modulation, however they are not very stable, because of the modal redistribution in the fiber.

Evanescent field sensors

They are especially useful for detecting chemical species. Their main disadvantage is the low interaction between the measurand and the light (i.e. the low amplitude of modulation); you can improve the sensitivity by using special fibers.

The sensors coupling two fibers

These extrinsic sensors are often used for measuring displacements. There are lots of possible configurations but most often, you have a low rate of coupling, so you have to use multimode fibers or extra optics.

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