Figure 10. Bragg grating response.
4.3 Phase Modulated Fiber Optic Sensors
Phase modulated sensors use changes in the phase of
light for detection. The optical phase of the light passing
through the fiber is modulated by the field to be detected.
This phase modulation is then detected
interferometerically, by comparing the phase of the light in
the signal fiber to that in a reference fiber. In an
interferometer, the light is split into two beams, where one
beam is exposed to the sensing environment and
undergoes a phase shift and the other is isolated from the
sensing environment and is used for as a reference. Once
the beams are recombined, they interfere with each other
[5].