In this presentation, we report a series of dynamic optical security features based on light field display elements. We have developed a light field shaping algorithm to generate the freeform micro-structures according to any predefined angular intensity distributions.
Compared to the conventional phase retrieval algorithms and diffractive optical elements (DOE), our algorithm and micro-structures have two main improvements. Firstly, our algorithm supports a larger phase delay to avoid rainbow colors. The phase delay of the conventional phase retrieval algorithms ranges from 0 to 2π. The phase delay of our algorithm ranges from 0 to more than 10π. Secondly, our algorithm eliminates the discontinuity of micro-structures to reduce speckle noise.
Depending on the freeform micro-structures, the light field display elements realize a series of dynamic optical security features, including dynamic patterns and 3D patterns. The characteristics are as followed:
1\. Stereoscopic: parallax is achieved simultaneously in both horizontal and vertical directions.
2\. Robust: compatible with general lighting conditions, such as sunlight, cellphone flashlight, bulb and lamp tube.
3\. Achromatic: the freeform micro-structures have no rainbow colors.
4\. High-resolution: pixel density larger than 1000 dpi and each pixel can project light according to a predefined angular intensity distribution.
5\. Integratable: Fabry-Perot filter and surface plasmon polarition (SPP) structure can be integrated.