A holographic display method includes calculating a hologram, displaying it on a spatial light modulator (SLM) and illuminating it with coherent light. The hologram includes hologram pixels each having a hologram pixel value. The hologram is calculated using steps including: performing the inverse Fourier transform of the product of an object field and a negative quadratic phase exponential representative of positive optical power; and restricting each calculated hologram pixel value to one of a plurality (greater than two) of allowable pixel values to form a constrained hologram, which is displayed on the SLM. Each light-modulating pixel of the SLM is operable in a plurality of light-modulation levels corresponding to the plurality of allowable pixel values. The SLM is illuminated with coherent light to form a replay field including conjugate images: a real holographic reconstruction and a virtual holographic reconstruction having greater intensity than that of the real holographic reconstruction.

A system and method comprise a light source; a spatial light modulator including a substantially transparent material layer and a phase modulation layer; an imaging device configured to receive a light from the light source as reflected by the spatial light modulator, and to generate an image data; and a controller. The controller provides a phase-drive signal to the spatial light modulator and determines an attenuating wavefront of the substantially transparent material layer based on the image data.

A replicator assembly includes reflective, transmissive, and transparent elements. The reflective element receives and reflects a hologram of a HUD system. The transmissive element includes a partially transmissive portion that receives a reflection of the hologram from the reflective element, outputs N replications of the hologram, and reflects N−1 replications of the hologram. The partially transmissive portion is implemented as a continuous transmission neutral density filter across different phase regions. The phase regions of the partially transmissive portion correspond respectively to the N replications. N is an integer greater than or equal to 2. The reflective element reflects the N−1 replications of the hologram. The transparent element is disposed between the reflective and transmissive elements and guides the N replications of the hologram between the reflective and transmissive elements. The reflective, transmissive and transparent elements are implemented as a replicator and collectively provide the N replications of the hologram.

A projector arranged to project an image within a display area on a display plane. The image comprises a light feature. A light sensor is spatially separated from the display plane. In an aligned state, light forming the light feature of the image on the display plane is at least partially disposed around the light sensor. In the aligned state, substantially no light forming the light feature impinges on the light sensor. The aligned state defines a selected alignment between the display area and the display plane (i.e. a selected position of the display area on the display plane).

A direct-retina holographic projection system includes first and second spatial light modulators (SLMs) and a control module. The first SLM receives a beam of light and dithers the beam of light at a predetermined frequency to provide multiple instances of the beam of light. The second SLM receives the instances of the beam of light, displays an encoded phase hologram of a graphic image to be projected, and diffracts the instances of the beam of light to provide instances of the encoded phase hologram with the same graphic image but multiplied with dithered wavefronts. The control module: iteratively adjusts a parameter of the first SLM to generate the instances of the beam of light; and controls operation of the second SLM to, based on the instances of the beam of light, display multiple instances of the graphic image on a retina of an eye of a viewer.

There is provided a method of projection using an optical element (502,602) 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 (604a) to produce first holographic data. Light is spatially modulated (504,603a) 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 (502,602) by illuminating a first region (607) of the optical element (602) with the first spatially modulated beam. The first lensing effect (604a) compensates for the optical power of the optical element in the first region (607). Advantageous embodiments relate to a head-up display for a vehicle using the vehicle windscreen (502,602) as an optical element to redirect light to the viewer (505,609).

A holographic image display system comprising a processor receiving image data at an input and producing output hologram data based on the image data. The image data comprises three-dimensional image data that is separable into a plurality of two-dimensional image layers at different image planes. The processor is configured to: a) perform a space-frequency transform on each image layer to provide a transformed image layer, b) apply a focus factor to each transformed image layer, c) apply a pseudo-random phase factor to each transformed image layer, and d) sum the transformed image layers to form a holographic sub-frame, e) repeat steps (c) and (d) for a plurality of iterations, applying a different pseudo-random phase factor to the transformed image layers in each iteration to form a plurality of holographic sub-frames; and f) drive a spatial light modulator with the holographic sub-frames in rapid temporal succession to generate a holographic image.

The goal of computer generated holography (CGH) is to synthesize custom illumination patterns by shaping the wavefront of a coherent light beam. Existing algorithms for CGH rely on iterative optimization with a fundamental trade-off between hologram fidelity and computation speed, making them inadequate for high-speed holography applications such as optogenetic photostimulation, optical trapping, or virtual reality displays. We propose a new algorithm, DeepCGH, that relies on a convolutional neural network to eliminate iterative exploration and rapidly synthesize high resolution holograms with fixed computational complexity. DeepCGH is an unsupervised model which can be tailored for specific tasks with customizable training data sets and an explicit cost function. Results show that our method computes 3D holograms at record speeds and with better accuracy than existing techniques.

Methods and apparatus to calibrate spatial light modulators are disclosed. Examples include processor circuitry to execute and/or instantiate instructions to provide a greyscale image to a spatial light modulator (SLM) to define voltages to be applied to individual pixels of the SLM. The voltages associated with pixel values in the greyscale image. The pixel values arranged in a double-slit grating pattern. The SLM to produce an interference pattern based on the double-slit grating pattern. The processor circuitry is to determine a phase difference between first and second gratings of the double-slit grating pattern based on the interference pattern. The processor circuitry is to generate a phase curvature based on the phase difference.

A display system for presenting a holographic image to a viewer may comprise a coherent light source, a display element, and a computing device operatively connected to the coherent light source and the display element, the coherent light source emitting a light that enters the display element from the same side of the viewer, and the display element comprising a liquid crystal layer and a partially-transmissive-partially-reflective layer, wherein the computing device is configured to provide a control signal to the display element to present the holographic image, wherein the liquid crystal layer receives light from the light source and is controlled by the control signal to modulate a phase of the light from the light source, and wherein the partially-transmissive-partially-reflective layer receives light from the liquid crystal layer and reflects the light back through the liquid crystal layer to the viewer.