Multiwavelength polarization insensitive lenses based on dielectric metasurfaces with meta-molecules

Abstract: Metasurfaces are nano-structured devices composed of arrays of subwavelength scatterers (or meta-atoms) that manipulate the wavefront, polarization, or intensity of light. Like other diffractive optical devices, metasurfaces suffer from significant chromatic aberrations that limit their bandwidth. Here, we present a method for designing multiwavelength metasurfaces using unit cells with multiple meta-atoms, or meta-molecules. Transmissive lenses with efficiencies as high as 72% and numerical apertures as high as 0.46 simultaneously operating at 915 nm and 1550 nm are demonstrated. With proper scaling, these devices can be used in applications where operation at distinct known wavelengths is required, like various fluorescence microscopy techniques.

• The paper introduces a meta-molecule-based design that minimizes chromatic aberration in dual-wavelength dielectric metasurface lenses.
• The authors demonstrate lenses with up to 72% efficiency and a numerical aperture of 0.46 at 915 nm and 1550 nm.
• Experimental results validate near diffraction-limited focusing, highlighting the method's promise for advanced optical applications.

Multiwavelength Polarization Insensitive Lenses Based on Dielectric Metasurfaces with Meta-Molecules

The paper explores the design and implementation of multiwavelength polarization-insensitive lenses using novel dielectric metasurfaces composed of meta-molecules. This approach aims to address the chromatic aberration challenges typically associated with metasurface lenses. The lenses presented in this study demonstrate significant advances in their operational efficiency and numerical aperture across specific wavelengths, thus highlighting the versatility and potential of dielectric metasurfaces in optical applications.

Metasurfaces are compact optical devices that manipulate light through arrays of sub-wavelength scatterers, known as meta-atoms. These scatterers can control various properties of light, such as its wavefront, polarization, and intensity. However, they are intrinsically prone to chromatic aberration, a limitation that narrows their operational bandwidth. The authors propose a multi-wavelength metasurface design utilizing unit cells with multiple meta-atoms, dubbed meta-molecules. This strategy capitalizes on dielectric transmitarrays that facilitate high transmission and precise subwavelength spatial manipulation of phase and polarization.

The study introduces transmissive lenses that exhibit efficiencies up to 72% and numerical apertures reaching 0.46. These lenses operate seamlessly at two distinct wavelengths—915 nm and 1550 nm. The underlying principle involves the precise arrangement of scatterers with varying geometrical configurations; these induce specific phase shifts in the transmitted light, effectively sculpting the desired wavefront. This design effectively minimizes chromatic dispersion by addressing the predominant source of dispersion in metasurfaces: the wrapping of phase around geometrical boundaries.

The authors provide experimental validation for their proposed method by fabricating and characterizing a dual-wavelength lens. The characterization reveals nearly diffraction-limited focusing at both wavelengths, with no significant secondary focal points, which firmly corroborates the theoretical predictions. Despite the high numerical aperture, the design realization demonstrates efficient focusing at specified wavelengths. It is noted that while focusing efficiency is higher at 1550 nm, some optimization may be necessary for improved efficiency at shorter wavelengths like 915 nm.

Analyzing future implications, this method shows promise for applications requiring dual-wavelength operations, such as advanced fluorescence microscopy techniques where different wavelengths are used for excitation and detection. Additionally, the adaptability of the meta-molecule platform is conducive to future developments in fields requiring complex lens functionalities across multiple wavelengths (e.g., color imaging systems).

The research delineates a step forward in metasurface technology, providing a framework to overcome inherent material dispersion limitations using innovative design principles. While not achieving full achromatic performance across continuous bandwidths, this approach signifies a pivotal progression toward practical and efficient multi-wavelength metasurface lenses. Looking forward, further exploration into scaling properties, material enhancements, and refined fabrication methods could potentiate broader applications and increased device performance.