There is provided a head-up display for a windscreen having spatially variant optical power. The head-up display comprises a diffuser arranged to display an image. The diffuser is shaped to compensate for the spatially variant optical power of the windscreen. A holographic projector may be provided, which is arranged to project the image for display onto the diffuser; the holographic projector comprises a spatial light modulator arranged to apply a phase-delay distribution to incident light, wherein the phase-delay distribution comprises phase-only data representative of an object; the projector further comprises Fourier transform means arranged to perform a Fourier transform of phase modulated light received from the spatial light modulator and to form the image on the diffuser.

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.

An optical device is provided that exhibits a variable optical effect upon illumination. The optical device has a diffractive structure comprising: a portion of a first kinoform diffractive structure that encodes a first image, arranged to form a first diffractive region (11) of the diffractive structure; and a portion of a second kinoform diffractive structure that encodes a second image, arranged to form a second diffractive region (13) of the diffractive structure; wherein the first diffractive region and the second diffractive region are laterally separate; and each of the first diffractive region and the second diffractive region are discernible by the naked human eye. Methods of manufacture of such optical devices are also disclosed.

We describe a LCOS (liquid crystal on silicon) telecommunications light beam routing device, the device comprising: an optical input; a plurality of optical outputs; a LCOS spatial light modulator (SLM) in an optical path between said input and said output, for displaying a kinoform; a data processor, coupled to said SLM, configured to provide kinoform data for displaying said kinoform on said SLM; wherein said kinoform data defines a kinoform which routes a beam from said optical input to a selected said optical output; wherein said data processor is configured to input routing data defining said selected optical output and to calculate said kinoform data for routing said beam responsive to said routing data; and wherein said data processor is configured to calculate said kinoform data by: determining an initial phase pattern for said kinoform; calculating a replay field of said phase pattern; modifying an amplitude component of said replay field to represent a target replay field for said beam routing, retaining a phase component of said replay field to provide an updated replay field; performing a space-frequency transform on said updated replay field to determine an updated phase pattern for said kinoform; and repeating said calculating and updating of said replay field and said performing of said space-frequency transform until said kinoform for display is determined; and outputting said kinoform data for display on said LCOS SLM.

Fast processing of information represented in digital holograms is provided to facilitate generating a phase-only hologram for displaying 3-D holographic images representative of a 3-D object scene on a display device. A holographic generator component (HGC) can receive or generate visual images, comprising depth and parallax information, of a 3-D object scene. A hologram processor component can downsample an intensity image of a visual image of the 3-D object scene using a uniform or random lattice to facilitate converting the intensity image to a sparse image. The hologram processor component can generate a complex 3-D Fresnel hologram, comprising the depth and parallax information, based on the sparse image using a fast hologram generation algorithm. The hologram processor component modify the magnitude of the pixels of the complex hologram to a defined homogeneous value to facilitate converting the complex hologram to a phase-only hologram.

There is provided a method of projection using an optical element having spatially variant optical power. The method comprises combining Fourier domain data representative of a 2D image with Fourier domain data having a first lensing effect to produce first holographic data. Light is spatially modulated with the first holographic data to form a first spatially modulated light beam. The first spatially modulated light beam is redirected using the optical element by illuminating a first region of the optical element with the first spatially modulated beam. The first lensing effect compensates for the optical power of the optical element in the first region.

There is provided a method of projection using an optical element having spatially variant optical power. The method comprises combining Fourier domain data representative of a 2D image with Fourier domain data having a first lensing effect to produce first holographic data. Light is spatially modulated with the first holographic data to form a first spatially modulated light beam. The first spatially modulated light beam is redirected using the optical element by illuminating a first region of the optical element with the first spatially modulated beam. The first lensing effect compensates for the optical power of the optical element in the first region.