Investigation on Photonic Crystal Fiber Sensing Using Metallic Rods

Abstract

In the recent few years, the photonic crystals have offered a potential platform for a broad range of applications in many domains. Many photonic crystal fibers such as in nonlinear devices, fiber-optic communications, high-power transmission, fiber lasers, highly sensitive gas sensors, and other fields have recorded high values of throughput. There has been noteworthy contribution of such components in different fields of miniature sizes, compactness, long term stability etc. The photonic crystals consist of periodic dielectric structures that have alternative low and high values of refractive index components. There is repetition of refractive index values after particular time duration that is of the order of the wavelength of light. The objective of this dissertation is to design and analyse various light confining optical designs based on photonic crystal fibers. The transmission and propagation characteristics curves are studied with the help of electromagnetic beam envelopes and electromagnetic frequency domain for finding the shifts. For confining light in the core region, parametric sweep is added for finding the fundamental mode. This is done with the help of Comsol software. The transmission and propagation curves are for these structures are also investigated. The transmission of light can be studied with the help of Maxwell equations. The Maxwell’s equations are solved using Finite Element Method (FEM) approach. These curves give information about the amount of light confined and traversed in the metallic rods. Firstly, an optical elliptical resonator is presented having metallic rods in the core region. The elliptical resonator is optimized for its performance as generating three times more value of electric field norm than ring resonator. By introducing appropriate material having desirable refractive index, varying the geometrical parameters, the electric filed and transmission efficiency is increased which results in red shift of the resonance wavelength. These modifications help to achieve enhanced sensitivity and quality factor in the resonator. Among all the materials, Silicon Nitride seems to be the most appropriate choice based on the light transmission with an average sensitivity of 500 nm/RIU obtained by variation of refractive index and semi minor axis width. Further, we investigated the design of seven layered hexagonal shaped photonic crystal fiber consisting of gold nanowires in the innermost layer. The PCF consists of particular values of Lattice constants and refractive indices for attaining maximum confinement of light in the core region. Here three gold nano rods in each of the innermost layer air hole are employed for sensing applications. The graphs for different propagation constants are plotted as a function of resonance wavelength and results are analysed which reveals optimum effective area, zero dispersion wavelength plot, effective mode index values, minimum confinement losses and attenuation with respect to wavelength. For the above designed structures, the EMBE AND EWFD methods are implemented using Comsol software, where these structures are analysed critically from the obtained results.