Catenary-based phase change metasurfaces for mid-infrared switchable wavefront control

Abstract

Active wave manipulation by ultracompact meta-devices is highly embraced in recent years, but a major concern still exists due to the lack of functional reconfigurability. Moreover, the phase or amplitude discontinuities introduced by collective response of discrete meta-atoms make current meta-devices far from practical applications. Here, we demonstrate actively tunable wavefront control with high-efficiency by combining catenary-based meta-atoms for intrinsic continuous phase regulation with the chalcogenide phase change material (PCM) of Ge2Sb2Te5. First, switchable beam deflection is demonstrated in a wide mid-IR range between 8 μm and 9.5 μm with ‘on’ and ‘off’ states for beam steering between anomalous and normal specular reflections. Second, a switchable meta-axicon for zero order Bessel beam generation is demonstrated with full width at half maximum (FWHM) as small as ∼0.41 λ (λ = 12 µm). As a result, our scheme for active and continuous phase control potentially paves an avenue to construct active photonic devices especially for applications where large contrast ratio is highly desirable, such as optoelectronic integration, wavefront engineering and so on.

Catenary optics: a perspective of applications and challenges

“…In this year, a catenary array was firstly used to generate continuous and linear geometric phases, and then catenary optics was formally proposed [6]. Later, many high-performance devices have been designed based on catenary optics, such as ultra-wide-angle metalenses [8,20,21], catenary-based chiral spectrometers [22], vortex beam generators [6], and so on [23][24][25]. Then, as research progressed, the catenary electromagnetics and extreme-angle catenary optics were proposed in 2018 and 2021 [7,8], respectively.…”

“…In addition, topology optimization provides an idea to further improve the efficiency and bandwidth of catenary structures; however, how to efficiently optimize large-area nonperiod continuous structures is still the focus of current research. Due to the high efficiency and broadband property of catenary structures, high-performance and multi-functional catenary-shaped devices have been widely studied, including chiral spectrometers [22], wide-angle metalenses [8,20,21], and tunable wavefront controllers [25,46]. As illustrated in figure 3(b), a broadband and high-efficiency mid-infrared chiral spectrometer based on a catenary array has been recently proposed [22].…”

“…Furthermore, active wavefront modulation has attracted great attention recently [49][50][51]. By combining the continuous catenary structures with phase change materials, efficient and active dynamic wavefront modulation can be achieved [25,46]. As shown in figure 3(d), a Ge 2 Sb 2 Te 5 -catenary hybrid metasurface is constructed for switchable specular reflection and Bessel beam generation [25].…”

“…By combining the continuous catenary structures with phase change materials, efficient and active dynamic wavefront modulation can be achieved [25,46]. As shown in figure 3(d), a Ge 2 Sb 2 Te 5 -catenary hybrid metasurface is constructed for switchable specular reflection and Bessel beam generation [25]. The switch between two functionalities can be achieved by thermally or electrically triggering the Ge 2 Sb 2 Te 5 phase transition, thus enabling dynamic tuning of the mid-infrared wavefront.…”

Polarization-multiplexed metaholograms with erasable functionality

“…Metasurfaces have emerged over the past decade as special planar devices for multi-functional and precise wave control 5 These authors contribute equally to this work. * Author to whom any correspondence should be addressed.…”