Design and Numerical Analysis of an Infrared Cassegrain Telescope Based on Reflective Metasurfaces.

Song Yue,Ran Wang,Dongliang Zhang,Huifang Guo,Zhe Zhang,Kunpeng Zhang,Lianqing Zhu,Haining Yang,Tonghui Dou,Zichen Zhang

doi:10.3390/nano11112904

Abstract

Reflective imaging systems such as Cassegrain-type telescopes are widely utilized in astronomical observations. However, curved mirrors in traditional Cassegrain telescopes unavoidably make the imaging system bulky and costly. Recent developments in the field of metasurfaces provide an alternative way to construct optical systems, possessing the potential to make the whole system flat, compact and lightweight. In this work, we propose a design for a miniaturized Cassegrain telescope by replacing the curved primary and secondary mirrors with flat and ultrathin metasurfaces. The meta-atoms, consisting of SiO2 stripes on an Al film, provide high reflectance (>95%) and a complete phase coverage of 0~2π at the operational wavelength of 4 μm. The optical functionality of the metasurface Cassegrain telescope built with these meta-atoms was confirmed and studied with numerical simulations. Moreover, fabrication errors were mimicked by introducing random width errors to each meta-atom; their influence on the optical performance of the metasurface device was studied numerically. The concept of the metasurface Cassegrain telescope operating in the infrared wavelength range can be extended to terahertz (THz), microwave and even radio frequencies for real-world applications, where metasurfaces with a large aperture size are more easily obtained.

Highlights

Refractive and reflective optical components are the two main basic categories of modern optical systems
The telescope is a kind of typical optical system which is especially important in the field of astronomical observations
We found that a random size error of up to 25% is allowable for the metasurface device to function correctly—a value much greater than that of traditional Cassegrain telescopes based on curved mirrors [1,4,5]

Summary

Introduction

Refractive and reflective optical components are the two main basic categories of modern optical systems. Li et al demonstrated for the first time a Cassegrain telescope based on two flat, ultrathin metasurfaces operating in the infrared wavelength range [22], opening up a new avenue to circumvent difficulties faced by reflective optics with curved surfaces. To tackle the abovementioned challenges, we propose in this work another type of metasurface Cassegrain telescope based on a propagation phase manipulation mechanism, with SiO2 and Al as the constituent materials. The metasurface Cassegrain telescope proposed and numerically demonstrated in this work provides an alternative design towards ultrathin, flat optical imaging systems, which can be scaled-up for real-world applications if we switch from infrared to the terahertz (THz) or micro-wave regimes, where metasurface devices with large apertures are more obtained

Design and Simulation Methods

Findings

Conclusions