4. Fiber Optic Sensor Types
4.1 Intensity Based Fiber Optic Sensors
Intensity-based fiber optic sensors rely on signal
undergoing some loss. They are made by using an
apparatus to convert what is being measured into a force
that bends the fiber and causes attenuation of the signal.
Other ways to attenuate the signal is through absorption or
scattering of a target. The intensity-based sensor requires
more light and therefore usually uses multimode large core
fibers [5]. There are a variety of mechanisms such as
microbending loss, attenuation, and evanescent fields that
can produce a measurand-induced change in the optical
intensity propagated by an optical fiber. The advantages of
these sensors are: Simplicity of implementation, low cost,
possibility of being multiplexed, and ability to perform as
real distributed sensors. The drawbacks are: Relative
measurements and variations in the intensity of the light
source may lead to false readings, unless a referencing
system is used [15].
One of the intensity-based sensors is the microbend
sensor, which is based on the principle that mechanical
periodic micro bends can cause the energy of the guided
modes to be coupled to the radiation modes and
consequently resulting in attenuation of the transmitted
light. As seen in Figure 6, the sensor is comprised of two
grooved plates and between them an optical fiber passe