Figure 7. Evanescent wave fiber optic chemical sensor.
4.2 Wavelength Modulated Fiber Optic Sensors
Wavelength modulated sensors use changes in the
wavelength of light for detection. Fluorescence sensors,
black body sensors, and the Bragg grating sensor are
examples of wavelength-modulated sensors. Fluorescent
based fiber sensors are being widely used for medical
applications, chemical sensing and physical parameter
measurements such as temperature, viscosity and
humidity. Different configurations are used for these
sensors where two of the most common ones are shown in
Figure 8. In the case of the end tip sensor, light propagates
down the fiber to a probe of fluorescent material. The
resultant fluorescent signal is captured by the same fiber
and directed back to an output demodulator [18].