Metasurface Device with Helicity‐Dependent Functionality

Abstract

To construct PSOEs, two anisotropic substrates [ 7,8 ] or a structure with form-birefringent [ 9,10 ] have been traditionally used to impose the desired phase delay for the two cross-polarizations of incident light. Although these devices prove to be effective, it is challenging for the etching depth control especially when some extreme phase profi les are needed. Besides, these devices suffer from the limited phase levels and the large pixel size due to the current fabrication techniques.Benefi ting from the easy fabrication and the fl exible control of the light propagation, metasurfaces have provided new opportunities to realize virtually fl at optics. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] In comparison with the traditional PSOEs, which realize the birefringence by carefully designing the structure of each pixel, the metasurface provides a much easier way by directly merging different optical elements together with each one working for a particular incident polarization. Refl ective-type metasurface holograms have been demonstrated to reconstruct two interchangeable images [ 27,28 ] by controlling the linear polarization state of the incident light. Although the previously proposed metasurfaces have shown their unique advantages such as broadband [ 27 ] and wide fi eld of view, [ 28 ] further application is hindered by the limited phase levels [ 27 ] and binary modulation [ 28 ] of the holograms since most optical elements such as a lens or an axicon are required to precisely manipulate the phase of the wavefront.Driven by miniaturization and system integration, ultrathin, multifunction optical elements are urgently needed. Traditional polarization-selective optical elements are mainly based on birefringence, which is realized by using the well-designed structure of each phase pixel. However, further reduction of the pixel size and improvement of the phase levels are hindered by the complicated fabrication process. An approach is proposed to realize a metasurface device that possesses two distinct functionalities. The designed metasurface device, consisting of gold nanorods with spatially varying orientation, has been experimentally demonstrated to function as either a lens or a hologram, depending on the helicity of the incident light. As the phase of the scattered light is controlled by the orientation of the nanorods, arbitrary phase levels and dispersionless phase profi le can be realized through a much simpler fabrication process than the conventional device. This approach provides an unconventional alternative to realize multifunction optical element, dramatically increasing the functionality density of the optical systems.

Advances in Full Control of Electromagnetic Waves with Metasurfaces

“…By utilizing the polarization-dependent phase response, devices based on the PB phase have the capability of controlling two waves with opposite polarities in different manners, such as dual-polarity meta-lenses [ 44,45 ] and polarization switchable holograms. [ 46,47 ] However, the manipulation effi ciency of such single nonmagnetic metasurfaces made of passive materials, either V-shaped nanostructures or PB phase metasurfaces, suffers from a theoretical upper limit 25%, which thus restricts their practical applications. [ 48 ] …”

Metasurfaces-based holography and beam shaping: engineering the phase profile of light

“…Although less attractive for some applications, such property is highly useful for many applications necessitating different processing of polarization states such as polarization convertors and analyzers [24,46,63,110,111], polarization multiplexing [24,27,28], etc.…”

“…The ability of metasurfaces to provide high-resolution control over the phase profile of optical beam, render them very attractive for many applications but in particular for holography and beam shaping [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. Indeed, studies on metasurfaces-based holography and beam shaping (primarily at mid and far IR) begun emerging more than a decade ago [11,12,31] where recent studies utilizing metallic and dielectric nano-structure demonstrated devices for short-IR and visible [5,20].…”

Multifunctional Metasurfaces Based on the “Merging” Concept and Anisotropic Single-Structure Meta-Atoms

“…Unfortunately, these meta-atoms typically do not satisfy the 100%-efficiency criterion established for PB metasurfaces [54] and, thus, one type of meta-atoms can generate background noise in addition to the desired functionalities. As a result, such meta-devices typically Such a "merging" concept has been straightforwardly applied to realize many other multifunctional meta-devices [58,[61][62][63][64][65]. Figure 1c presents a reflective bifunctional meta-device which can form a holographic image of a 'flower' or a 'bee' as the helicity of incident light changes from left CP (LCP) to right CP (RCP) [63].…”