Study On Micro/Nanofiber Sensors Based On Evanescent Fields

Similar to electronic devices, photonic devices also show the trendfor miniaturization and integration. The ability to inject, guide, andmanipulate light on the wavelength or subwavelength scale is of greatimportance to achieve ultracompact photonic devices and dense photonicintegrated circuits (PICs). Micro/Nanoscale waveguides are one of thefundamental building blocks for micro/nanophotonics devices, and havebeen the subject of intensive research in the last few years. Amongst,micro/nanofiber, one of the typical micro/nanoscale waveguides, featuredwith simple fabrication, excellent diameter uniformity and surfacesmoothness, low loss, tight-confinement ability, enhanced evanescentfields and large waveguide dispersion for guiding light within the visibleand near infrared spectral ranges, is being extensively interested.This thesis focuses on several novel micro/nanofiber sensors basedon evanescent fields. Firstly, waveguiding properties of micro/nanofibers in various environments are studied with exact solution of Maxwell's equations. Single mode conditions, propagation constants, and power distribution of the fundamental mode are studied. These provide the theoretical basis for developing various micro/nanophotonics devices. Meanwhile, based on theoretical modelling, here a highly-sensitive sensor employing a micro/nanofiber-assembled Mach-Zehnder structure is suggested and investigated. The sensor is used to measure the refractive indices change of liquids. Besides, the important parameters, including sensitivity and detection limit, are also estimated. Secondly, a novel micro/nanofiber sensor based on white light interferometer is presented. It is used to measure the refractive indices of glucose solutions of different concentrations. Experimental results prove its practicality and worth. Lastly, an interferometric sensor using single micro/nanofiber is developed. The sensor is based on the principle of optical heterodyne technique. It overcomes the difficulties of micro-operation in multiple-sensing arm scheme.Compared to other fiber optic sensors, the sensors demonstrated here show advantages such as compact size, high sensitivity, and easy integration with the optoelectronic devices. The stability of the sensor can be applied to many fields, such as biological, chemical and pharmaceutical and process control applications.