Abstract
Metamaterials (MMs) are subwavelength-structured materials that have been rapidly developed in this century and have various potentials to realize novel phenomena, such as negative refraction, cloaking and super-resolution. Theoretical proposals for super-resolution image transfer using metallic thin films were experimentally demonstrated at ultraviolet and violet wavelengths from 365 to 405 nm. However, the most preferred wavelengths of optical imaging are green wavelengths around 500 nm, because optical microscopy is most extensively exploited in the area of biotechnology. In order to make the super-resolution techniques using MMs more practical, we propose the design of a stratified metal-insulator MM that has super-resolution image transfer modes at green wavelengths, which we here call hyper modes. The design assumed only Ag and SiO2 as constituent materials and was found employing Bloch-state analysis, which is based on a rigorous transfer-matrix method for the metal-insulator MMs. It is numerically substantiated that the designed stratified metal-insulator metamaterial (SMIM) is capable of forming super-resolution images at the green wavelengths, and optical loss reduction is also studied. We discuss the results derived by the Bloch-state analysis and by effective medium models usually used for the metal-insulator MMs and show that the Bloch-state analysis is more suitable to reproduce the experimental data.
Highlights
Super-resolution (SR) image transfer in metamaterials (MMs) was stimulated by a paper on SR imaging by a silver slab [1] and has been developed theoretically [2,3,4] and experimentally [5,6,7,8,9]
In addition to the SR imaging, it was found that the stratified metal-insulator metamaterial (SMIM) enable intriguing phenomena, such as isotropic negative refraction [10,11]
The experimental demonstrations on the SR imaging and the negative refraction were mostly conducted at the ultraviolet (UV) to violet wavelength range (365 to 405 nm), where SMIMs of finite thickness show high transmittance (T) up to tens of a percent
Summary
Super-resolution (SR) image transfer in metamaterials (MMs) was stimulated by a paper on SR imaging by a silver slab [1] and has been developed theoretically [2,3,4] and experimentally [5,6,7,8,9]. It was reported that SMIMs, including insulators of a high refractive index of about 2.4 [8,10,11], have a transmission band at a longer wavelength range than SMIMs of a low refractive index of about 1.5. It has not been reported that SMIMs works at about 500 nm or green wavelengths, even if the high-index insulators are incorporated. To make the SR optical imaging more practical, it is highly desirable to move the working wavelengths to the green wavelengths, In addition, well-known low-index insulators, such as SiO2 , have an advantage in making the fabrication procedure more feasible and low cost, because they are widely used and common materials. The result is consistent with recent theoretical implications [24,25]
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