Fig. 1. Schematic illustration depicting the conceptual implementation of the cascaded LC holographic encryption. Three independent holographic images are reconstructed with LC_a, LC_b, and cascaded LC_a and LC_b.

Fig. 2. Flow chart of the iterative algorithm with the calculated LC phase holograms. (a) Modified Gerchberg–Saxton algorithm. Fast Fourier transform and inverse fast Fourier transform are denoted as FFT and iFFT. The red, blue, and green parts of the flow chart represent the parts involved in the generation of phase profiles of φ_c, φ_a, and φ_b. |E_g|² corresponds to the amplitude of a standard Gaussian beam. (b) Output phase information for LC elements (LC_a and LC_b).

Fig. 3. Experimental setup and two LC elements (LC_a and LC_b) for secret sharing. (a) Experimental setup to record the holographic images. The optical path contains either one LC element or both the LC_a and LC_b. LP, linear polarizer; QWP, quarter-wave plate. (b) Designed phase profile of LC director distributions and the crossed polarized microscopic textures of LC_a and LC_b; the orthogonal polarizer and analyzer are represented by crossed white arrows. Scale bar: 75 µm.

Fig. 4. Theoretically and experimentally reconstructed holographic images of letters “N,” “J,” “U,” “O,” “K,” and “L” for cascaded holographic encryption. (a), (b) Reconstructed holographic images (letters “N” and “J” from LC_a and LC_b, and letters “O” and “K” from LC_d and LC_e) in the single-LC framework; (c) holographic images of letters “U” and “L” in the cascaded LC framework. These images are marked by white dotted lines.

Fig. 5. Electrically dynamic optical encryption based on cascaded LC holography. (a) Schematic illustration of the electric switching of LC hologram with different applied voltages (0 V and 14 V); (b) four basic holographic images in the cascaded LC framework with different combinations of applied voltages; (c) electrically dynamic optical encryption based on cascaded LC holography for the scenario, where ciphers or passwords are sent to multiple receivers. Scale bar: 250 µm.