This flat superlens is the first single lens that can focus the entire visible spectrum (including white light) at high resolution at the same point. It uses a titanium dioxide nanofilm group to average the wavelength of the focused light and eliminate chromatic aberration.
The flat surface of the hyperlens uses nanostructures to concentrate, and promises to replace the huge curved lenses used in current optics with simple and flat surfaces and trigger an optical revolution. However, these hyperlenses still have limitations in the spectrum they can concentrate on. Now, a research team at Harvard University's John A. Paulson School of Engineering and Applied Science (SEAS) has developed the first single lens that focuses the entire visible spectrum, including white light, at the same point with high resolution. This can only be achieved by superposition in conventional lenses.
This study was published in Nature Nanotechnology.
Focusing the entire visible spectrum and white light (a combination of all spectral colors) is very challenging because each wavelength passes through the material at a different speed. For example, the red wavelength is faster than blue when passing through the glass, so the two colors will not reach the same position at the same time. This difference causes the focus to be different and produces image distortion called chromatic aberration.
Cameras and optical instruments use multiple curved lenses of different thicknesses and materials to correct for these chromatic aberrations, which of course increases the size of the device.
Federico Capasso is a senior author of the study and a member of the Applied Physics and SEAS Vinton Hayes senior electrical engineering research team led by Professor Robert L. Wallace. He said: "The superlens is superior to conventional lenses. The super lens is thinner. Easy to manufacture and cost-effective. This breakthrough extends these advantages throughout the visible field. This is the next big step forward.
The Harvard University Technology Development Office (OTD) has protected intellectual property related to the project and is seeking opportunities to commercialize it.
The superlens developed by Capasso and his team tested a titanium dioxide nanofilm stack to average the wavelength of the focused light and eliminate chromatic aberrations. Previous studies have shown that by optimizing the shape, width, distance and height of the nanofilm, light of different wavelengths can be focused at different distances. In this latest design, the researchers created pairs of nano-film units that simultaneously control the speed of light at different wavelengths. The paired nanofilms control the refractive index on the super-surface and adjust different degrees of retardation for light passing through different films, ensuring that all wavelengths reach the focus at the same time.
"One of the biggest challenges in designing a wide-band lens with no chromatic aberration is to ensure that the wavelength of the output of the superlens points reaches the focus at the same time," said Wei Ting Chen, a postdoctoral researcher at SEAS and the first author of the paper. “By combining two nanofilms into one component, we can adjust the speed of light in the nanostructured material to ensure that all wavelengths in the visible light are focused at the same point using a single superlens, relative to the composite In the case of standard achromatic lenses, this greatly reduces the thickness of the lens and the complexity of the design."
Alexander Zhu, one of the co-authors of the study, said: "Using our achromatic lenses, we can perform high-quality white light imaging, which is another step towards the goal of integrating them into common optical devices such as cameras. â€
Next, the researchers' goal is to enlarge the lens diameter to about 1 cm. This will lead to a range of new possibilities, such as applications in virtual and augmented reality.
This paper was co-authored by Vyshakh Sanjeev, Mohammadreza Khorasaninejad, Zhujun Shi and Eric Lee. It is partially supported by the Air Force Scientific Research Office. Part of this work will be carried out at the Center for Nanosystems (CNS), a member of the National Nanotechnology Coordination Infrastructure (NNCI), supported by the National Science Foundation.
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