Contents

#### **Preface XI**


Preface

This book contains 10 chapters focusing on the new developments and practical applications of optical sensors. Laboratory experiments and field investigations of new and emerging op‐ tical sensors are presented. Some data analysis methods are also described. Chapter 1 dis‐ cusses principle and practical implementation of fiber-optic and free space Michelson interferometer for sensor applications. Considering the coherence length of a He-Ne laser, the Michelson interferometer potentially allows for measurement of far objects, where a sig‐ nal is guided in an optical fiber. In addition, the interferometer can be miniaturized or built as a fiber optic based sensor. Chapter 2 reviews recent development of excessively tilted fi‐ ber grating as optical sensors for various physical parameters such as strain, twist, loading, refractive index (RI) and liquid level sensing. The use of mesoporous polymers for optical sensors is discussed in Chapter 3. Chapter 4 describes the use of photonic crystal laser for gas sensor that provides some advantages over the ones based on traditional semiconductor lasers. The emission and operation parameters of this laser as well as measured spectra of H2O at 1910 nm are also presented in this chapter. Chapter 5 presents Whispering Gallery

Mode (WGM)-based and other fiber optic sensors for biomedical applications.

Fiber Bragg gratings (FBGs) have been widely employed for various optical fiber sensing applications. In Chapter 6, two different FBG-based sensor networks are proposed and demonstrated utilizing passive system design. The first design is based on a 25 km cavity length erbium-doped fiber (EDF) ring laser for detecting multiple FBG sensors in the net‐ work. The second design is based on a multi-ring passive sensing architecture, which does not have any active components in the entire network. Thus, the proposed system can facilitate the construction of a reliable FBG sensing network for large-scale and multipoint architecture. Chapter 7 presents the development of bio and chemical sensors based on Surface Plasmon Resonance (SPR) in a plastic optical fiber (POF). The POF sensor con‐ figurations are presented to monitor an aqueous environment (refractive index around 1.333), with a resolution ranging from 10-4 to 10-3 (RIU). A wide range of optical sensors have been utilized in agriculture, which include sensors used to analyze soil attributes to the ones installed in combines to measure protein content in wheat grains while they are being harvested. Chapter 8 specifically discusses optical sensors to measure agricultural crop reflectance. Chapter 9 presents recent advances in nanostructured based detector tech‐ nology, materials and devices for optical sensing applications. An overview of recent works on a variety of semiconductors and advanced materials such as GaN, ZnO, Si/SiGe, In‐ GaAs and CNT for optical sensing applications is thoroughly discussed in this chapter. In the final chapter, a new luminophore application method is proposed and demonstrated
