Composite Functional Metasurfaces for Multispectral Achromatic Optics (1609.08275v1)

Abstract: Nanostructured metasurfaces offer unique capabilities for local control of the phase and amplitude of transmitted and reflected optical waves. Based on this potential, a large number of metasurfaces have been proposed in recent years as alternatives to standard optical elements. In most cases, however, these elements suffer from large chromatic aberrations, thus limiting their usefulness for multi-wavelength or broadband applications. Here, in order to alleviate and correct the chromatic aberrations of individual diffractive elements, we introduce dense vertical stacking of independent metasurfaces, where each layer comprises a different material, and is optimally designed for a different band within the visible spectrum. Using this approach, we demonstrate the first triply RGB achromatic metalens in the visible range and perform color imaging with this lens. We further demonstrate functional beam shaping by constructing a self-aligned integrated element for Stimulated Emission Depletion (STED) microscopy and a lens that provides anomalous dispersive focusing. These demonstrations lead the way to the realization of superachromatic ultrathin optical elements and multiple functional operations, all in in a single nanostructured ultrathin element.

• The paper introduces a novel multilayer metasurface architecture that achieves multispectral, triply achromatic optics in the visible spectrum.
• It employs dense vertical stacking of nanoantenna layers made from gold, silver, and aluminum to target red, green, and blue wavelengths while minimizing chromatic aberrations.
• Experimental demonstrations reveal focusing efficiencies of 5.8%–8.7% and promising applications in color imaging and high-resolution STED microscopy.

Composite Functional Metasurfaces for Multispectral Achromatic Optics

The paper "Composite Functional Metasurfaces for Multispectral Achromatic Optics", authored by Ori Avayu, Euclides Almeida, Yehiam Prior, and Tal Ellenbogen, presents an innovative approach to overcoming chromatic aberrations inherent in metasurface-based optical elements. This research introduces a architectural framework for metasurfaces that enables multi-spectral achromatic optics through the dense vertical stacking of independent metasurfaces, each optimized for a specific wavelength band within the visible spectrum.

In particular, this paper proposes a multilayer metasurface design to address the persistent issue of chromatic aberrations observed in conventional diffractive optics. Each layer in the metasurface stack is composed of nanoantennas made from different metals—gold, silver, and aluminum—chosen for their unique interactions with specific parts of the spectrum (red, green, and blue light, respectively). The multilayered metasurfaces operate on the principle of Localized Surface Plasmon Resonances (LSPR), providing control over spectral responses with minimal inter-layer crosstalk. The design is supported by well-defined design rules and is fabricated using established nano-lithography techniques.

Notably, the paper demonstrates the first triply achromatic metalens operating in the visible range. Experimental validation showcases functional devices such as a composite lens for color imaging and a novel optical component for STED microscopy that offers tightly focused beams with enhanced spatial resolution. Additionally, a lens demonstrating anomalous dispersive focusing is developed, enhancing its application in multi-wavelength optical systems.

Key findings include the successful fabrication of metasurfaces with focusing transmission efficiencies between 5.8% and 8.7%, aligning closely with theoretical expectations. Moreover, the authors underline advancements in reducing chromatic aberrations, illustrating a reduction to less than 10% residual power of undesired wavelengths, achieved through optimal material selection and design precision.

From a practical standpoint, these multilayer metasurfaces have the potential to revolutionize integrated opto-electronic devices, offering ultrathin, multifunctional optical elements that could supplant more cumbersome traditional optics. Theoretically, this research underscores the versatility of nanostructured metasurfaces, with a flexibility in design that can be expanded to address broader spectral ranges beyond visible light and improve efficiency toward 100%.

Future research directions may explore extending these stacked metasurfaces across different frequency bands, potentially leading to hyperspectral optical elements. Additionally, refinement in nanofabrication techniques could further enhance the quality factors of resonators, thereby diminishing residual aberrations and fostering improved device performance.

Overall, this paper exemplifies how leveraging the nanophotonic properties of metasurfaces can produce remarkable advancements in optical technology, paving the path for complex, ultrathin, and efficient photonic devices.