Partial Cloaking by Graded Index Photonic Crystals

摘要

Since the first proposal of the idea of optical cloaking, huge research effort has been spent to implement hiding objects. We propose a broad band all-dielectric partial (unidirectional) cloaking device that hides arbitrary shaped objects. The cloaking structure is designed utilizing graded index (GRIN) photonic crystals. Refractive index distribution of the structure is chosen as a hyperbolic secant profile. In order to generate desired index profiles, both low and high dielectric backgrounds are chosen. The main principle of the cloaking in the study is separating the beam into two main parts while propagating through the composite device. Each part of the separated beam is strongly focused at the center of the stacked GRIN devices. Then these beams diverge and converge repeatedly without deteriorating the planar input field profile. This mechanism dramatically reduces the intensity at the center of the device. Therefore, existence of an object at the cloaked region almost does not affect wave front of the exiting beam due to this special light manipulation mechanism. In this manner, an observer cannot detect the hidden object. GRIN medium is a special type of inhomogeneous environment and light propagation is greatly affected by the presence of GRIN. Any partial cloaking solution as long as being practical and broadband in nature can be preferred. In this case, material selection and easy transferring the design to other electromagnetic spectrum regions become crucial. Therefore, the proposed idea in this work collects these desirable features.