Measurement Systems with Optical Waveguide Sensors

Abstract

In this chapter is devoted to a special kind of optical sensors based on guided light. Optical waveguides (Lopez-Higuera in Handbook of optical fibre sensing technology. Wiley, 2002 [1]) have proven to be a powerful tool for sensing using optical radiation, see Sect. 10.1. Moreover, the optical fiber itself can be designed to act as an intrinsic sensor, see, for example, Sect. 10.2 where an optical grating is shown to be integrated within the fiber core. A large number of further optical measurement techniques may be based on optical fibers, such as, for example, the technique of evanescent field sensing (Sect. 10.3). At first, we will have a brief look at light propagation in an optical waveguide (Sect. 10.1). In particular, optical waveguides are used as sensor elements or as a transport medium to direct light to the location of measurement. Then, an optical interference effect presents in the core of an optical waveguide or optical fiber will be evaluated. This interference effect is based on the integration of a so-called fiber-Bragg grating, FBG, as will be explained in Sect. 10.2. Many important applications result from such kind of FBG-based fiber-optic sensors (FOSs). In the last Sect. 10.3 of this chapter, an attenuation effect which can occur in specially designed optical waveguides will be elucidated, i.e., the evanescent wave propagating in the waveguide cladding. It will be shown, how evanescent field sensing (EFS) and attenuated total reflection (ATR) can efficiently contribute to interesting applications of optical, fiber-based measurement systems.