During the last decade, active metasurface has attracted significant attention from academia and industry because of its unparalleled advantages over conventional technologies. Active metasurface using electrically controlled liquid crystal (LC) is one of the most promising types of active metasurface towards industrial applications. In this work, we report a silicon metasurface immersed in a nematic liquid crystal for transmission amplitude modulation. Tunable resonance was realized by applying an AC voltage and the resonance was tuned in the spectral range of 1524 nm ~ 1573 nm, which covers the telecommunication C band. The corresponding phase shift at 1555 nm with a maximum value approaching 2π was measured using a Michelson interferometer, which supports the tuning of metasurface resonance by LC. As a result, the maximal modulation depth in transmission amplitude of 94% as experimentally recorded at 1530 nm. In addition, the high quality of LC photoalignment on metasurface was evaluated by examining the transmitted light intensity between crossed polarizers. The response time of sub-milliseconds can be obtained, thanks to the thin cell thickness of only 1 μm. The high alignment quality and fast response time demonstrated in this work shows a promising future for metasurface-integrated liquid crystal on silicon (meta-LCoS) spatial light modulators (SLMs), especially for telecommunication applications.
Optically addressed spatial light modulator (OASLM) has attracted an increasing amount of attention due to its enormous potential in digital holography. Solution-processed ZnO nanoparticle (NP) is particularly promising in OASLM as a photosensor because ZnO NP-based OASLM can provide high resolution, large panel size, and economical production cost. However, it is still challenged by slow switching speed due to a long fall time (off time) and it takes tens of seconds for ZnO NP-based OASLM to switch off, which is limiting its application in dynamic digital holography. In this paper, the optimization in the fall time of ZnO NP-based OASLM is presented. The reduction in fall time was achieved by thermal annealing of ZnO NP, which decreases the effect of charge carrier trapping. Moreover, the fall time was further shortened by introducing a SiO2 layer between ZnO NP and liquid crystal layer so that the charge trapping at the interface is weakened. The shortest fall time of 0.99s was achieved in reflective OASLM, incorporating PEDOT:PSS-ZnO NP heterojunction. The heterojunction was also characterized in terms of IV characteristics and its barrier height was measured by CV measurement. The reduction of fall time discussed in this paper is valuable and it makes ZnO NP-based OASLM attractive for dynamic holographic displays.
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