Objective Scattering is one of the major obstacles to optical imaging. However, scattering media in daily life sometimes play the role of privacy protection, such as PDLC, a widely used and electrically switchable novel scattering media. However, studies on PDLC (Polymer Dispersed Liquid Crystal) have mainly focused on materials, structures, and preparation methods. The optical scattering properties of PDLC, especially on the destruction of object-field information corresponding to the protection of privacy, have not been reported in detail. So that, this study investigated the scattering properties of a typical PDLC and analyzed the performance differences between PDLC and other commonly used diffusers, finding that optical homogenization cannot be the only indicator of PDLC design and preparation.

Methods This paper investigated the optical properties of a typical PDLC, including scattering characteristics, transparency, stability and electronically controlled characteristics, and analyzed the performance differences between PDLC and commercial diffusers. Then, we explored and analyzed the image recovery effect of two methods: one is direct imaging using ballistic light through lens, and the other is image recovery using scattered light by deconvolution (Wiener filtering).

Results and Discussions The results show that PDLC has a large scattering angle and optical memory effect range, so that its scattering distribution maintains correlation during angle change (Fig.1), and its scattering pattern does not change significantly at different voltages (Fig.2), showing a high proportion of ballistic light and a stable structure. However, compared with diffusers, PDLC is poor at reducing the zero-frequency light and enhancing the scattering effect. The ballistic light information can still be collected by the lens and used for imaging (Fig.4). Nevertheless, PDLC is able to achieve object hiding effects close to those of 10° diffusion angle diffusers without the assistance of an optical device (Fig.3), providing some privacy protection. What’s more, we explored two image recovery methods. One is to use the ballistic light through the lens for direct imaging, which found that the scattering effect of PDLC is mainly manifested in the homogenization of the broad-spectrum background light resulting in the decrease of the target imaging contrast. And target information can be effectively obtained by optical filtering processing and direct imaging can be realized (Fig.5). The other is the use of scattered light by deconvolution (Wiener filtering) to achieve a certain degree of image recovery (Fig.8). Compared to the diffusers, the presence of the ballistic photon component in the PDLC reduces the scattered light component but leaves a certain light intensity background in the scattering pattern, resulting in a lower contrast and poorer uniformity of the scattered image.

Conclusions The results show that large scattering angle and optical memory effect range expose the disadvantage of PDLC, a high percentage of ballistic light. Nevertheless, PDLC, has some privacy protection function, whose ability of hiding object close to 10° diffusion angle diffusers without the assistance of optical devices. However, PDLC is still worse than diffusers in terms of reducing ballistic light and enhancing scattering effect. Then, we explored and analyzed two image recovery methods for the scattering characteristics of PDLC. One is to use the ballistic light through the lens for direct imaging, which found that the scattering effect of PDLC is mainly manifested in the homogenization of the broad-spectrum background light resulting in the decrease of the target imaging contrast. And the other is the use of scattered light by deconvolution (Wiener filtering) to achieve a certain degree of image recovery. The experimental results demonstrate that current PDLC still have risks in privacy protection if it only relies on the optical homogenization effect to assess performance. Therefore, the design and preparation of PDLC must provide more comprehensive scattering optical characteristic indexes as a test standard.