21.1 INTRODUCTION

Various transduction mechanisms using optical fibers to sense physical parameters have been demonstrated. The mechanisms discussed in this chapter exploit the modulation of optical intensity, phase, and state of polarization. The light may be modulated either inside or outside the fiber. With the exception of microbending, amplitude modulation is performed by some means outside the fiber. Alternatively, phase and polarization modulation generally are performed within the fiber.

All of these transduction approaches may employ multimode or single-mode components. However, intensity modulation usually employs multimode components while phase modulation typically uses single-mode components. As such, intensity-modulated sensors tend to be less expensive and less sensitive.

In Sec. 21.2, various transduction methods are discussed. A description of the optical components is given in Sec. 21.3. Techniques for fabricating temperature sensors are given in Sec. 21.4. Static and dynamic pressure sensors are considered in Sec. 21.5. Accelerometers and rate-of-rotation sensors are discussed in Secs. 21.6 and 21.7, respectively. Finally, electric/magnetic field sensors are described in Sec. 21.8. References are included in Sec. 21.9. The approach taken below is to describe the basic principles in a simple form and to give appropriate references for those who desire to pursue a specific topic in more detail.

21.2 FIBER-OPTIC SENSOR TRANSDUCTION

Various modulation techniques used for transduction are described in this section.