Indefinite metamaterials for optical applications
Date of Issue2016
School of Materials Science and Engineering
A*STAR Singapore Institute of Manufacturing Technology
The resolution of conventional optical systems is limited because of Abbe’s diffraction limit, which dictates that objects placed closer than approximately half the wavelength of light used cannot be completely resolved. Hence, it becomes imperative to find means of performing near-field (Superlensing) and label-free real time far-field super-resolution imaging (hyperlensing) at the nanoscale. Although by utilizing anisotropic permittivities, metal-dielectric multilayers have been successful in reconstructing the high-frequency components from sub-λ objects, yet they remain cumbersome and expensive to make. Most of the multilayer structures require multiple vacuum deposition cycles and are plagued by stringent requirements on surface roughness of metallic layers. In contrast to the multilayer structure here we propose a 3D hyperbolic metamaterial model composed of metallic nanorods arranged in sea-urchin geometry as a hyper-lensing device, which is capable of projecting and magnifying diffraction limited information into the far-field at Near-infrared (NIR) frequencies. The hyperlens generates a band of flat hyperbolic dispersions in spherical coordinates, which in turn supports the propagation of high wave-vector spatial harmonics leading to far-field super-resolution imaging. Using full-wave Finite-difference time-domain (FDTD) simulations with diffraction limited trimer, quadrumer and ringed objects etched on thin perfect electric conductor (PEC) films, we show that the hyperlens model can achieve magnification factors of up to 10X in the far-field (~4.5λ from object’s surface) under a light source with a wavelength of 1 μm, with successful resolution down to 220 nm (~λ/5). The magnified image field distribution projected into the far-field is shown to follow the object under reduction in symmetry. A possible method for the fabrication of envisaged AuNWA-PDMS composite metamaterials is presented. The method shown is capable of yielding thin flexible polymer films embedded with free-standing metallic nanowires. Further, fabrication of diffraction-limited objects for both Superlensing (slits on film) and hyperlensing (slits on curved Cr-caps) are presented. These results are important for making progress in the realization of real-time bio-molecular imaging systems, eliminating the need for near-field scanning, destructive electron microscopy and various image post-processing techniques.
DRNTU::Science::Physics::Optics and light