Optical fibers transmission principles

Explain the connection between the attenuation loss of the optical fiber used for transmission of information and the sensing principles utilizing an evanescent field. 

Walt (1998) described the principle of optical sensing using fibers. An optical fiber consists of two concentrically arranged optically transparent media an inner ring, called the core, carries the optical signal, and a thin outer ring, called the clad (made of a lower refractive index material). The refractive index mismatch at the interface of the two media acts as a mirror to help the transmission of light from one end of the fiber to the other end. The phenomena in play here is that of total internal reflection (Walt 1998). 

Based on the basic performance of optic fiber sensors, Krohn (1986) divided optic fiber sensors into two basic classes. In the first class, the transmission of the fiber is directly affected by the physical phenomena being sensed and is referred to as an intrinsic optic fiber sensor. The second class is for optic fiber position sensors which detect position changes and are sensitive to changes in physical property. There are usually five types of sensors according to their different working principles intensity modulated, transmitting, reflective, micro bending... 

Based on the principle of the Raman microscope, a regular transmission and reflex ion optical microscope has been modified to unable tunable pulsed laser injection as well as fluorescence collecting via an optic fiber up to a intensified CCD camera allowing time resolved records. For this purpose, aU optics was replaced to support high-energy laser pulses. Such equipment allows the following (Panczer et al. 2003) ... 

Optical property refers to a material s response to exposure to electromagnetic radiation and, in particular, to visible light. This chapter first discusses some of the basic principles and concepts relating to the nature of electromagnetic radiation and its possible interactions with solid materials. Then it explores the optical behaviors of metallic and nonmetal-lic materials in terms of their absorption, reflection, and transmission characteristics. The final sections outline luminescence, photoconductivity, and light amplification by stimulated emission of radiation (laser), the practical use of these phenomena, and the use of optical fibers in communications. 

The aim while using optical fibers is to find out how much and how far signals can be sent per unit time. The possible transmission range of Gl POFs is dominated by two major fartors. This section outlines the general principles of bandwidth and attenuation. 

Figure 16.3 (a) Principles of fiber Bragg grating (FBG) optical sensors (b) details showing the notch in the transmission spectrum and the peak in the refiection spectrum at the Bragg wavelength [9]. 

---