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ABSTRACT
Optical techniques are used for large number of sensing and metrological applications. The conventional methods based on free- space monitoring is effective only for line of sight and suffers from undesired misalignments and external perturbations. Guided- wave sensing adds to intrinsic advantages of optical techniques the possibility of guiding the light beam in a confined and inaccessible medium, thus allowing more versatile and less perturbed measurements.
Fiber and integrated optics technology were primarily developed for telecommunication applications. However, the development of high quality and competitive price optoelectronic components and fibers have largely contributed to the expansion of guided wave technology for sensing as well.
Fundamental of Wave Guiding
According to ray theory of light propagation, when light impinges at the interface between two transparent media, it is partially reflected and partially refracted.
An optical fiber consists of layered cylinders of glass or plastic. Inner and outer cylinders, namely ‘core’ and ‘cladding’, have refractive indices n1 and n2, respectively. Any ray impinging at the core-cladding interface with an incident angle greater than θc is undergoing multiple reflections within the core, in which it results trapped and propagates.
Fiber and integrated optics technology were primarily developed for telecommunication applications. However, the development of high quality and competitive price optoelectronic components and fibers have largely contributed to the expansion of guided wave technology for sensing as well.
Fundamental of Wave Guiding
According to ray theory of light propagation, when light impinges at the interface between two transparent media, it is partially reflected and partially refracted.
An optical fiber consists of layered cylinders of glass or plastic. Inner and outer cylinders, namely ‘core’ and ‘cladding’, have refractive indices n1 and n2, respectively. Any ray impinging at the core-cladding interface with an incident angle greater than θc is undergoing multiple reflections within the core, in which it results trapped and propagates.
