Focus‐Tunable Planar Lenses by Controlled Carriers over Exciton

Abstract

degree of resolution is surpassing the level of human perceivability, a differentiated approach to further develop this technology is necessary. One such approach can be the application of an optically focusing device onto the display panels that controls the optical paths of individual pixels in order to facilitate holographic display. Nevertheless, conventional lenticular lenses [1] limit the design of the displays due to its high thickness, whereas conventional ultrathin diffractive lenses lack focusing controllability. Therefore, the realization of innovative technologies such as 3D display, [2] virtual reality (VR), [3] augmented reality (AR), [4] and so on requires both ultrathin and focus-tunable optical devices. Recently, microsized tunable lenses based on phase delays in anisotropic liquid crystals [5] are used to control focal lengths, and dielectric elastomer actuators (DAEs) [6] have demonstrated significant potential as electrically tunable flat lenses. Moreover, tunable metasurfaces [7] using phase-changing materials such as graphene or combinations of complexes like microelectromechanical systems (MEMS) [8] and DAEs have also demonstrated their potential. While recent studies on nanoscale diffractive lenses demonstrate their potential as possible candidates for thin-film display applications, their narrow focal ranges limit their application. Graphene, however, may realize focal controllability for its unique optoelectric property; due to its unique band structure among 2D materials, its carriers can be controlled by adjusting the Fermi level. Furthermore, due to the bandgap property of graphene, the intraband excitation of carriers is dominant over the interband excitation of carriers, which results in enhanced photonic transmission and reduced absorbance. Utilizing this property, graphene-based ultrathin focusing device is fabricated that alters its optical characteristics when direct-current voltage is applied producing vertical fringe-specific electric field. The proposed device demonstrates 8.6% change in focal length and 48.85% focusing efficiency at wavelength of 405 nm. Overall, this study on electrically tunable ultrathin microlens introduces potential for holographic displays and expands the research scope in future display technologies.

Tunable metasurfaces towards versatile metalenses and metaholograms: a review

“…Electrically tunable metalenses can be realized by applying an external voltage bias on active materials, such as LCs [76][77][78][79][80][81][82] and graphene. [83][84][85][86][87][88][89] Transmission-type terahertz metalenses that combine dielectric metasurfaces with photopatterned LCs have achieved tunable chromatic aberration. 78 When the voltage bias is applied to the LCs, their geometric phase modulation vanishes, and only the resonant phase in the metalenses remains, so the function of the device changes from achromatic to dispersive focusing [Fig.…”

Sub-Diffraction Photon Trapping: The Possible Optical Energy Eigenstates within a Tiny Circular Aperture with a Finite Depth

“…One of the most attractive and popular applications of these effects has taken place with graphene interfaces lately [25][26][27][28][29][30][31]. The almost linear dispersion relation of graphene near Dirac points makes it easy to control the optical transmissivity of the layer as it turns out to be a unique semi-metal.…”

Electrically tunable metasurfaces: from direct to indirect mechanisms

“…Additionally, electrically operated nanophotonic devices can be easily extended to industrial uses. Several pioneering studies have already implemented active hologram displays [20,[104][105][106][107][108][109][110][111][112], varifocal metalens [39,[113][114][115][116][117], and LiDAR [18,38,118] as experimental applications, and are expected to be a great inspiration for smart windows, next-generation communication systems, and photonic ICs.…”