Varifocal Metalens Using Tunable and Ultralow‐loss Dielectrics

Abstract

The field of flat optics that uses nanostructured, so-called metasurfaces, has seen remarkable progress over the last decade. Chalcogenide phase-change materials (PCMs) offer a promising platform for realizing reconfigurable metasurfaces, as their optical properties can be reversibly tuned. Yet, demonstrations of phase-change metalenses to date have employed material compositions such as Ge 2 Sb 2 Te 5 , which show high absorption in the visible to near-IR wavelengths particularly in their crystalline state, limiting the applicability. Here, by using a low-loss PCM Sb 2 Se 3 , for the first time, active polarization-insensitive phase-change metalenses at near-IR wavelengths with comparable efficiencies in both material states are shown. An active metalens with a tunable focusing intensity of 95% and a focusing efficiency of 23% is demonstrated. A varifocal metalens is then demonstrated with a tunable focal length from 41 to 123 μm with comparable focusing efficiency (5.7% and 3%). The ultralow-loss nature of the material introduces exciting new possibilities for optical communications, multi-depth imaging, beam steering, optical routing, and holography.

Toward Accurate Thermal Modeling of Phase Change Material‐Based Photonic Devices

“…[ 18 ] More recently, PCMs have been integrated into metasurfaces in order to develop tunable properties. [ 1,19–24 ]…”

“…[18] More recently, PCMs have been integrated into metasurfaces in order to develop tunable properties. [1,[19][20][21][22][23][24] To better understand the operation of these devices and rationally guide their design, considerable efforts have been dedicated to precise modeling of PCMs' phase transition behavior. [25,26] However, to date, the vast majority of the investigations have focused on electronic memory configurations, which do not apply to photonic devices where electrothermal switching via external micro-heaters rather than direct current injection is employed.…”

Differentiated design strategies toward broadband achromatic and polarization-insensitive metalenses

“…Conventional refractive optical components, allowing precise control of the optical wavefront by relying on gradual phase accumulations as light propagates through bulky media, are generally bulky, costly, and time-consuming to manufacture with high precision, which significantly hinders their application, especially in miniaturized and highly integrated devices. In recent years, metasurfaces, consisting of subwavelength-spaced phase shifters at an interface, have emerged as a flexible platform for shaping the wavefront by tailoring the phase, amplitude, and polarization at will, enabling the realization of various ultracompact optical components, ranging from lenses, 1 – 6 holograms, 7 – 10 and carpet cloaks 11 , 12 to beam deflectors 13 – 15 Among these devices, metalenses, metasurfaces encoded with hyperbolical phase profiles, have attracted intense attention due to their great potential for future efficient portable or wearable optical devices with small footprints and light weights.…”

Wavelength-actuated varifocal and polarization-insensitive metalenses assisted by monolayer single-celled phase-change metasurfaces

“…Among these devices, metalenses, imparting metasurfaces with hyperbolical phase profiles, have attracted intense attention due to their great potential for future efficient portable or wearable optical devices with small footprints and light weights. To date, various types of metalenses with versatile functions were implemented, spanning achromatic metalenses [15][16][17], tunable metalenses [7,18], varifocal metalenses [19][20][21], polarizationsensitive metalenses [22,23], and to other multi-functional metalenses [24][25][26][27][28][29][30][31].…”