Abstract
Resolution of the conventional lens is limited to half the wavelength of the light source by diffraction. In the conventional optical system, evanescent waves, which carry sub-diffraction spatial information, has exponentially decaying amplitude and therefore cannot reach to the image plane. New optical materials called metamaterials have provided new ways to overcome diffraction limit in imaging by controlling the evanescent waves. Such extraordinary electromagnetic properties can be achieved and controlled through arranging nanoscale building blocks appropriately. Here, we review metamaterial-based lenses which offer the new types of imaging components and functions. Perfect lens, superlenses, hyperlenses, metalenses, flat lenses based on metasurfaces, and non-optical lenses including acoustic hyperlens are described. Not all of them offer sub-diffraction imaging, but they provide new imaging mechanisms by controlling and manipulating the path of light. The underlying physics, design principles, recent advances, major limitations and challenges for the practical applications are discussed in this review.
Highlights
Curiosity and desire to see microscopic world have leaded the invention of the optical microscope
Optical microscopes became more useful and essential for the decades, but there is still a fundamental question how to achieve the spatial resolution below diffraction limit
Resolution achievable by using conventional optical microscope is intrinsically limited to approximately two hundred nanometers in visible light
Summary
Curiosity and desire to see microscopic world have leaded the invention of the optical microscope. Optical microscopes became more useful and essential for the decades, but there is still a fundamental question how to achieve the spatial resolution below diffraction limit. Resolution achievable by using conventional optical microscope is intrinsically limited to approximately two hundred nanometers in visible light. At 1930s, microscopes using electrons such as scanning electron microscope (SEM) [2] To overcome such limitations, far-field microscopy with super-resolution and bio-compatibility have been successfully developed and widely used. In addition to the development of such advanced imaging methods, various algorithms and techniques to realize super-resolution have been studied [18]. We will describe the new types of imaging approaches based on new optical materials called metamaterials which can provide the direct control and manipulation of electromagnetic properties to overcome diffraction limit. Since the lenses are named by proposers, not by social protocols, the boundaries of the divided groups may be ambiguous
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