Transformation Optics Based On Graded Dielectric Waveguide

In recent years, transformation optics based on metamaterials is an emerging research field,as it can modulate the propagation of photons and design many fascinating and perfect performing devices. But metamaterials usually require a modulation of permittivity, permeability or refractive index of every point in the space which make them difficult to be realized experimentally. However, in traditional planar dielectric waveguide, the effective index of waveguide modes is determined by the thickness of dielectric layer. We can change the effective index of the waveguide simply by change the thickness of dielectric media, absence of specially designed resonance structure and ohmic loss of metal pattern. Thus, we can realize low-loss broadband transformation devices with easy configuration if effective index is modulated in the way of changing the thickness of graded waveguide. In this paper, we do some research on the basic theory, fabrication process, measuring system of graded dielectric waveguide. Based on which, we design and realize a transformation bending device.First of all, we review the deve lopment of metamaterials based transformation devices. Several methods of realizing transformation devices are surveyed and relative merits of which are assessed. Then, we suggest to realize transformation device in graded dielectric waveguide because of simply fabrication process, low ohmic loss and scattering loss, broadband working width compared with metamaterials.We propose a simple and novel technic b fabricate graded waveguide as follows. Because of the wetting behavior of PMMA solution on the surface of silver, PMMA was spun-coated and self-assembled into a gradient thickness waveguide along the pre-set boundary duo to the surface tension. This method is easy and the surface of PMMA is smooth with scattering loss suppressed during propagation Then we observed unidirectional propagation and beam splitting of two modes in the gradient dielectric waveguide using home-built Quantum dot Fluorescence Imaging Microscopy(QDFIM).After that, we demonstrated numerical and experimental results of a transformation bending device in the QDFIM (605nm) excited by ultraviolet light (405nm) with low loss and large angle(90o). Then, we use the same technology to guide visual light along a irregular boundary designed at will.We could enlarge working bandwidth through increasing the thickness of PMMA. Besides, with carefully designed boundary, we can make more devices.