Broadband vectorial ultrathin optics with experimental efficiency up to 99% in the visible region via universal approximators

F Getman,A Burguete-Lopez,A Fratalocchi,M Makarenko

doi:10.1038/s41377-021-00489-7

Abstract

Integrating conventional optics into compact nanostructured surfaces is the goal of flat optics. Despite the enormous progress in this technology, there are still critical challenges for real-world applications due to the limited operational efficiency in the visible region, on average lower than 60%, which originates from absorption losses in wavelength-thick (≈ 500 nm) structures. Another issue is the realization of on-demand optical components for controlling vectorial light at visible frequencies simultaneously in both reflection and transmission and with a predetermined wavefront shape. In this work, we developed an inverse design approach that allows the realization of highly efficient (up to 99%) ultrathin (down to 50 nm thick) optics for vectorial light control with broadband input–output responses in the visible and near-IR regions with a desired wavefront shape. The approach leverages suitably engineered semiconductor nanostructures, which behave as a neural network that can approximate a user-defined input–output function. Near-unity performance results from the ultrathin nature of these surfaces, which reduces absorption losses to near-negligible values. Experimentally, we discuss polarizing beam splitters, comparing their performance with the best results obtained from both direct and inverse design techniques, and new flat-optics components represented by dichroic mirrors and the basic unit of a flat-optics display that creates full colours by using only two subpixels, overcoming the limitations of conventional LCD/OLED technologies that require three subpixels for each composite colour. Our devices can be manufactured with a complementary metal-oxide-semiconductor (CMOS)-compatible process, making them scalable for mass production at low cost.

Highlights

The production of lightweight and wearable optoelectronic devices is presently hampered by the bulky and expensive nature of traditional optical components[1,2,3]
An electromagnetic wave composed of a spectrum of waves with amplitudes 1⁄2si1ðωÞ; 1⁄4 ; sinðωÞ 1⁄4 siðωÞ (Fig. 1a, red arrows) impinges on an optical surface constituted by a complex distribution of dielectric nanostructures grown on a transparent substrate (Fig. 1b), generating both reflected s-n(ω) and transmitted s+n(ω) contributions propagating in different scattering directions (Fig. 1a, orange arrows)
A detailed demonstration of this result is presented in refs. 60,61, while here, we summarize the main aspects

Summary

Introduction

The production of lightweight and wearable optoelectronic devices is presently hampered by the bulky and expensive nature of traditional optical components[1,2,3]. The majority of transmissive flat optics designed to operate in the visible region exploit propagation phase shifts in truncated waveguides[22], using wavelength-thick structures in the range between 250 and 800 nm. While this approach works quite well at infrared frequencies, where commonly

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Conclusion