Effective control of light in gradient and wavy multilayered photonic structures

Photonics the science dealing with manipulation the flow of light, enables us to analyse and control the optical properties of engineered structures created, for instance, by periodic arrangement of photonic crystals. This branch of science, which laid its foundations by the seminal works of Lord Rayleigh in 1887, has had an important role in the formation of new technologies that revolutionized the 20th century. Here, by using the temporal and spatial dispersions of photonic crystals, direct control over the flow of light can be achieved with judiciously designed effective structures and, in result, advanced optical properties can be obtained. In this thesis, photonic structure designs for optical applications such as optical invisibility, beam steering, afocal zooming and spatial filtering are proposed by using two dimensional photonic crystals. In this context, first, a directional invisibility cloak design based on quadruple Luneburg lens system has been presented by examining various graded refractive index (GRIN) media. Specially, we show that an incident light can be rerouted around the region between junctions of the lenses without any direct interaction and hence, an object can be placed inside that dark zone to be rendered invisible. Thereafter, GRIN photonic crystals are combined with nematic liquid crystals (LCs) to design actively controllable beam steering and afocal lens systems without any mechanical movements. In order to actively control the incoming light, the polymer annular rods are infiltrated with nematic LCs and owing to the structural properties of the LCs, the effective refractive index profile of the GRIN medium is modified with an externally applied voltage. In this regard, beam steering with an angle change of ∆θout = 44° and a light magnification with maximum x 2.15 are obtained within the operational frequency ranges of a/λ = [0.10–0.15] and a/λ = [0.15–0.25]. Here a is the lattice constant and λ is the incident wavelength. In this section, the proposed structures are examined analytically via geometrical optics and then their numerical analysis are performed with the finite difference method (FDTD) method. Moreover, the cloaking effect was confirmed by conducting microwave experiments with the structure produced by three-dimensional printing technique. In the next chapter of the thesis, the design and analysis of wavy multilayer photonic structures is presented to achieve angular filtering in the Bragg configuration. Compared to the Laue configuration, where spatial filtering was previously examined, structures designed in the Bragg configuration are technologically more challenging to fabricate since the longitudinal periods of such structures must be shorter than the operational wavelength. As a solution to this challenge, designed multi-layer structures are fabricated by physical vapor deposition and their experimental verification is conducted in the visible light spectrum.