Figure 6. Intrinsic fiber optic sensor.
Another type of intensity based fiber optic sensor is the
evanescent wave sensor (see Figure 7) that utilizes the
light energy which leaks from the core into the cladding.
These sensors are widely used as chemical sensors. The
sensing is accomplished by stripping the cladding from a
section of the fiber and using a light source having a
wavelength that can be absorbed by the chemical that is to
be detected. The resulting change in light intensity is a
measure of the chemical concentration. Measurements
can also be performed in a similar method by replacing the
cladding with a material such as an organic dye whose
optical properties can be changed by the chemical under
investigation [17].