Circularly-polarized, semitransparent and double-sided holograms based on helical photonic structures

Junji Kobashi,Masanori Ozaki,Hiroyuki Yoshida

doi:10.1038/s41598-017-16517-9

Junji Kobashi, Masanori Ozaki + Show 1 more

Open Access

https://doi.org/10.1038/s41598-017-16517-9

Copy DOI

Abstract

Recent advances in nanofabrication techniques are opening new frontiers in holographic devices, with the capability to integrate various optical functions in a single device. However, while most efficient holograms are achieved in reflection-mode configurations, they are in general opaque because of the reflective substrate that must be used, and therefore, have limited applicability. Here, we present a semi-transparent, reflective computer-generated hologram that is circularly-polarization dependent, and reconstructs different wavefronts when viewed from different sides. The integrated functionality is realized using a single thin-film of liquid crystal with a self-organized helical structure that Bragg reflects circularly-polarized light over a certain band of wavelengths. Asymmetry depending on the viewing side is achieved by exploiting the limited penetration depth of light in the helical structure as well as the nature of liquid crystals to conform to different orientational patterns imprinted on the two substrates sandwiching the material. Also, because the operation wavelength is determined by the reflection band position, pseudo-color holograms can be made by simply stacking layers with different designs. The unique characteristics of this hologram may find applications in polarization-encoded security holograms and see-through holographic signage where different information need to be displayed depending on the viewing direction.

Highlights

Holography is a field of optics, which through the design of transmitted or reflected amplitude and/or phase patterns, enables the reconstruction of arbitrary wavefronts[1,2]
We demonstrate chiral-binary, pseudo-color holograms by stacking several devices designed to operate at different wavelengths and for different circular polarizations
It has recently been shown that the phase of light reflected from a cholesteric liquid crystal (ChLC) can be controlled by varying the geometric phase of the helical structure[14,15,16,17]

Summary

Introduction

Holography is a field of optics, which through the design of transmitted or reflected amplitude and/or phase patterns, enables the reconstruction of arbitrary wavefronts[1,2]. Recent advances in nanofabrication technologies are opening new frontiers, as ultra-compact devices with advanced, integrated optical functions (e.g., circular-polarization-dependent image generation) can be realized using the so-called meta-surface concept, in which engineered sub-wavelength structures are used to modulate the optical field[7,8,9,10,11,12]. We present a semi-transparent and reflective CGH that generates different wavefronts depending on the illumination side of the hologram. The device can be varied from fully reflecting to transmitting by the circular sense of the polarization illuminating the device, but only the reflected light is phase modulated, meaning that the device can be seen through under ambient conditions. We demonstrate chiral-binary, pseudo-color holograms by stacking several devices designed to operate at different wavelengths and for different circular polarizations. The unique characteristics of this hologram may find applications in polarization-encoded security holograms and holographic signage where different information need to be displayed depending on the viewing direction

Methods

Results

Conclusion