Multiple guidance of light using asymmetric micro prism arrays for privacy protection of device displays.

With increasing use of mobile displays outdoors, privacy-related issues have come to the fore. Therefore, in this study, we proposed a novel concept using directionally guided light transmission using double-sided asymmetric prism arrays for fabricating a privacy protection film for digital displays. The proposed film allows only the user in front of the display to see its contents using dual refraction in a prism array. Otherwise, when the display is viewed at an angle, it is difficult to recognize the contents due to the overlap of different letters. The optical path was analysed through ray-tracing simulations, and the performance of the film was quantified using an optical character recognition (OCR) method. To further enhance the effectiveness of the film, a metal film was applied on the vertical face of the micro prism arrays using an oblique deposition method. This metal-coated double-sided prism array film showed superior privacy-protecting performance compared to a conventional method based on the micro-louver structure.

Large-area fabrication of microlens arrays by using self-pinning effects during the thermal reflow process.

Generally, the fabrication of curved structures such as microlens arrays has been regarded as an expensive and complicated process. Here, we propose a facile method to form a microlens array with controlled lens curvature by combining residue-free nanoimprint lithography (NIL) with V-shaped molds and the successive thermal reflow procedure of the printed polymeric structures. The V-shaped molds used in this study enable the bottom substrate to be exposed after the NIL process when the initial thickness is controlled. Then, we use the thermal reflow to realize hemi-cylindrical curved lenses by applying heat. The polymers are self-pinned on the exposed substrate, which is strong enough to fix the boundary to not dewet or be flattened in the broad temperature range of the reflow process, which is essential for a large-area fabrication. Furthermore, we demonstrate the modulation of the focal lengths of the lenses by controlling the initial polymer thickness coated on a substrate.