ABSTRACT
In its simplest form, a fiber optic sensor consists of a light source, an optical fiber, a sensing element, and a detector as illustrated in the Figure 20.1. The light source may be a broadband, a light-emitting diode, or a laser, depending upon the nature of the sensor. When the sensing element is an essential part of the fiber, the sensor is called an intrinsic sensor. When the fiber is only used to guide light to and from the sensing element the arrangement is known as an extrinsic sensor, as depicted in Figure 20.2a and Figure 20.2b. Physical properties of light such as amplitude, frequency, phase, and polarization passing through the sensing element can be affected by the change
in the environment surrounding the sensing part of the sensor. These changes can easily be detected and are used to design a variety of sensors such as pressure, temperature, chemical, and biological.
