Metasurface optics for imaging applications
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Introduction Lenses are optical elements that collect or spread light toward a focal point. They are one of the most important elements in imaging systems. Advances in conventional lenses, such as refractive or diffractive lenses, have led to the development of various imaging systems such as telescopes, cameras, and microscopes, and have also had a major impact on the development of mobile or wearable devices in recent years.1 Although research related to improving the performance of conventional lenses has continued, next-generation imaging systems demand performance improvements beyond what is achievable with conventional lenses, and further development of novel optical technologies for compact and high-performance lenses is required. In recent years, metasurface optical elements have attracted much attention due to their great potential to advance photonics and optoelectronics. Metasurfaces are artificial photonic structures and are typically composed of two-dimensional arrays of subwavelength scatterers.2–7 The subwavelength scatterers, also called meta-atoms, are designed to have unique optical properties for spatial control of the amplitude, phase, polarization, or spectrum of light.8–18 The optical functions of metasurfaces are determined according to the geometry or material of meta-atoms, and they show unprecedented optical
properties not generally found in natural materials such as dielectrics and metals. Various optical devices have been developed by using metasurfaces, and one of the most important applications is a metasurface lens (called metalens), which is considered a promising candidate for the next generation of optical elements. In this article, we provide a brief overview of progress in the development of metalenses. We summarize basic principles and important features of metalenses along with their comparison with conventional lenses. We introduce several imaging applications using metalenses and discuss current issues and potential solutions. We conclude by providing an outlook and promising directions for further improvements.
Conventional lenses: Refractive or diffractive lens The primary role of optical elements such as lenses is to modulate an incoming wavefront into an appropriate shape. From a device perspective, the ability to control phase information of light in the spatial domain is required to implement optical elements. In this context, refractive lenses exploit refraction of light to implement a lens function (Figure 1a). Based on Snell’s Law of refraction, the lens curvature and composing material
Gun-Yeal Lee, Seoul National University, Republic of Korea; [email protected] Jangwoon Sung, Seoul National University, Republic of Korea; [email protected] Byoungho Lee, Seoul National University, Republic of Korea; [email protected] doi:10.1557/mrs.2020.64
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