Methods and devices for coherent holographic data channel techniques. Coherent techniques for data detection generally include homodyne and heterodyne detection. Techniques for quadrature homodyne detection, resampling quadrature homodyne detection, n-rature homodyne detection, and spatial wavefront demodulation. Coherent detection techniques in turn enable coherent channel modulation techniques such as phase modulation (including binary phase shift keying, or BPSK; phase quadrature holographic multiplexing, or QPSK; and quadrature amplitude modulation, or QAM). Coherent detection may also enable or improve the performance of other channel techniques such as partial response maximum likelihood (PRML), the various classes of extended PRML, and of noise-predictive maximum likelihood (NPML) detection.

Cryptographic techniques for encrypting images, and decrypting and reconstructing images, are provided to facilitate preventing unauthorized access to images. A holographic cryptographic component (HCC) generates complex holograms of multi-dimensional source images of a multi-dimensional object scene. The HCC generates phase holograms, based on the complex holograms, using a stochastic hologram generation process, and encrypts the phase holograms to generate encrypted holograms based on a random phase mask, which can be the private encryption key. At the decoding end, an HCC overlays a conjugate phase mask on the encrypted holograms to decrypt them, wherein the decrypted holograms are illuminated with a coherent light source to generate holographic images that reconstruct the source images. The source images are only reconstructed properly if the correct phase mask is used. If HCC applies the encryption process repetitively to the same source image, HCC can generate a different encrypted hologram in each run.

A metasurface structure including an array of sub-wavelength structures including a phase change material (PCM), encoded with different holographic images based on different phases of the PCM, the different phases including a first phase and a second phase. Phase transition between the first phase and the second phase occurs when the metasurface structure is thermally tuned. Each sub-wavelength structure in the array has a distinctive phase difference between the first phase and the second phase of the PCM.

An optical identifier including a recording surface, a plurality of deflection cells each of which has recorded thereon a range in which light to be diffracted is deflected, at least one spatial phase modulator which fills a space between the deflection cells on the recording surface, and a deposition layer which covers part or all of the recording surface. The deflection cells has a spatial frequency expressed in a form of a relief structure and are discretely formed on the recording surface at regular intervals away from each other. A variable color image is recorded by pixels defined by the deflection cells. The spatial phase modulator has thereon a distribution of phase differences recorded in a form of heights of the relief structure. The spatial phase modulator modulates a phase of light outputted from a point light source and displays a reproduced image.