Optical Transmission Characteristics Of Nanostructural Photonic Devices

Nanophotonics is a new developing technology which has been attracting much attention worldwide. One of the hot spot is the investigation of various functional photonic devices with nanopatterned structures. To explore the novel functions of the nano-structured devices as well as the theoretical design technique, in this thesis, the optical transmission characteristics including focusing, polarizing and filtering of nano-photon sieves (NPS) and compound nanogratings are investigated, respectively.We first analyze the field change of different components of electromagnetic wave vectors through the nano-photon sieves (NPS). The effects of the radius of nanoholes, number of rings, density modulation function and the thickness of the metallic layer of NPS on the characteristics of optical transmission are discussed. It is found that a subwavelenth focusing can be realized by appropriate designed NPS. By employing a nanohole array instead of the ring pattern in the conventional Fresnel micro-zone-plate (FMZP) and introducing an apodization modulation function on the density of the nanohole array, the side-lobes of the NPS are effectively suppressed to one fifth of that of the corresponding Fresnel micro-zone-plate (FMZP), and both the intensity distribution of focal spot and the side-lobes of focal spot exhibit better symmetric behavior than that of the FMZP.We also investigate the optical behaviors of multilayered nanograting structures and propose a novel device with compound functions of polarizing and filtering. Characteristics of both optical polarizing and filtering in the visible wavelength range with two different multi-layer subwavelength structures are investigated using numerical method. The effects of the refractive indices of the substrate and the transition layer, the thicknesses of the transition layer and the metallic layer, and the period and duty cycle of the grating on the behavior of the polarizing and filtering of the multilayered structure are discussed. Typical optimized multilayer structures are obtained. The results open new possibilities in designing, optimizing and fabricating novel multi-functional polarizing and filtering photonic devices using a single subwavelength structure.