Miniature optical planar camera based on a wide-angle metasurface doublet corrected for monochromatic aberrations (1604.06160v2)

Abstract: Optical metasurfaces are two-dimensional arrays of nano-scatterers that modify optical wavefronts at subwavelength spatial resolution. They are poised to revolutionize optics by enabling complex low-cost systems where multiple metasurfaces are lithographically stacked and integrated with electronics. For imaging applications, metasurface stacks can perform sophisticated image corrections and can be directly integrated with image sensors. Here, we demonstrate this concept with a miniature flat camera integrating a monolithic metasurface lens doublet corrected for monochromatic aberrations, and an image sensor. The doublet lens, which acts as a fisheye photographic objective, has a small $f$-number of 0.9, an angle-of-view larger than 60$^\circ\times$60$^\circ$, and operates at 850 nm wavelength with 70% focusing efficiency. The camera exhibits nearly diffraction-limited image quality, which indicates the potential of this technology in the development of optical systems for microscopy, photography, and computer vision.

• The paper presents a novel metasurface doublet design that corrects monochromatic aberrations and achieves near diffraction-limited imaging at 850 nm.
• It details a design using cascaded metasurface phase profiles and lithographically fabricated dielectric nano-posts, yielding a f-number of 0.9 and an angle-of-view over 60°×60°.
• Performance evaluation reveals approximately 70% focusing efficiency and effective aberration correction up to 30° incident angles, indicating strong potential for compact imaging systems.

Overview of "Miniature Optical Planar Camera Based on a Wide-Angle Metasurface Doublet Corrected for Monochromatic Aberrations"

The paper presented in this paper introduces an innovative approach to optical camera design using metasurfaces. Optical metasurfaces are two-dimensional arrays of nano-scatterers capable of altering optical wavefronts with high precision. These metasurfaces offer a novel method for producing compact, cost-effective optical systems. The research focuses on developing a miniature planar camera incorporating a metasurface lens doublet to correct monochromatic aberrations prevalent in single metasurface lenses.

Key Contributions

The authors report the design and fabrication of a metasurface doublet lens system that demonstrates significant advancements in correcting chromatic and monochromatic aberrations. This doublet lens acts as a fisheye photographic objective, exhibiting a small f-number of 0.9 and an extensive angle-of-view exceeding 60° × 60°. The operational wavelength is specified at 850 nm, with a commendable focusing efficiency of 70%. The doublet lens achieves a nearly diffraction-limited image quality, illustrating its potential for various optical applications in fields such as microscopy, photography, and computer vision.

Detailed Findings

This work leverages optical metasurfaces' capability to produce sophisticated planar optical systems. These systems are fabricated using lithographic techniques, facilitating precise alignment without the need for post-manufacturing calibration. The metasurface doublet lens surpasses the performance of a single metasurface lens by effectively correcting fundamental optical aberrations such as coma and astigmatism.

• Design and Simulation: The paper details the design of the metasurface doublet lens, achieved by cascading two metasurfaces with distinct phase profiles. Simulation results exhibit near-diffraction-limited focusing capabilities at various incident angles, affirming the design's robustness.
• Fabrication: The metasurface doublets are lithographically fabricated on a fused silica substrate. High transmission and phase control are realized through precise engineering of dielectric nano-posts made of amorphous silicon, offering phase coverage across 2π with exceptional transmission efficiency.
• Performance Evaluation: Experimental characterization demonstrates the optical performance of the doublet lens. Focal spots are nearly diffraction-limited up to 30° incident angles, validating the design efficacy. Furthermore, the setup exhibits focusing efficiency of approximately 70% under normal light incidence, with minor polarization dependency at oblique angles.

Implications and Future Directions

The demonstrated metasurface technology holds substantial promise for miniaturizing camera systems while preserving high optical performance. The planar design's compactness aligns well with current trends in reducing electronics and optical components' footprints. Specifically, the vertical integration approach presents a scalable path toward fully integrated optical-electronic systems.

Potential future developments include extending this approach to handle broadband operations and multiwavelength imaging, which are crucial for hyperspectral and color imaging applications. The integration of more advanced materials and fabrication techniques could further enhance operational bandwidth and efficiency. Additionally, improvements in pixel size and image sensor technology could synergistically augment the metasurface camera's imaging quality.

This paper positions metasurface technology as a formidable contender in developing next-generation optical devices, potentially impacting various domains such as consumer electronics, medical imaging, and surveillance systems.