Page 603 - Introduction to Information Optics

10.2. A Brief Review of Types of Fiber-Optic Sensors

,0.025

Fig. 10.11. Transfer function of fiber Fabry-Perot interferometer, /(<•/>) as a function of phase delay
<t> for difference reflection coefficients. Solid line: R — 0.5; dashed line: R — 0.95.

dl((f))/d(j>\ maj, no passive techniques have been developed for this complex
transfer function. In addition, at most values of static phase shift, the sensitivity
of the Fabry-Perot interferometer is zero.
On the other hand, when finesse, F, is small, the sensitivity of the Fabry-
Perot interferometer is not high. However, it offers a simple sensor configur-
ation, which does not require fiber couplers and does not incur the difficulties
associated with the multiple-beam approach outlined above.

10,2.4. FREQUENCY (OR WAVELENGTH) BASED
FIBER-OPTIC SENSORS

As described in Eq. (10.1), a light field is also a function of frequency (or
wavelength). The emitted light frequency or wavelength may also be influenced
by some types of perturbations. Thus, certain types of fiber-optic sensors can
also be built based on frequency or wavelength changes.
As an example, let us look at a fluorescent light-based temperature sensor
[20,21]. The fluorescent material is used at the sensing head of the fiber sensor.
Since the fluorescent lifetime of this material is temperature dependent, the