Holography

Holography is a technique for recording and later reconstructing the complete light field scattered from an object, including both the amplitude (brightness) and the phase (wavefront shape) of the light, so that the reconstructed image reproduces the depth, parallax, and perspective of the original scene. An ordinary photograph records only intensity and yields a flat image; a hologram records an interference pattern that, when illuminated, diffracts light back into a copy of the original wavefront. The recording medium is called a hologram, from the Greek holos (whole) and gramma (message), reflecting that it stores the whole of the optical information.

The method was invented by the Hungarian-British physicist Dennis Gabor, who conceived it in 1947 and published it in Nature in 1948, and who received the Nobel Prize in Physics in 1971 "for his invention and development of the holographic method". In virtual reality (VR) and augmented reality (AR), holography is relevant in two distinct ways. Microscopic holograms (holographic optical elements) are used as the see-through combiner optics inside many AR headsets and smart glasses, and true computer-generated holography is being researched as a display method that can reproduce correct depth cues, which conventional flat displays cannot. The word "holographic" is also widely used in product marketing for effects that are not holograms in the physical sense, a point of frequent confusion discussed below.

Origin and history

Gabor invented holography in 1948 while working at the British Thomson-Houston Company in Rugby, England, where he was looking for a way to improve the resolution of the electron microscope by correcting its spherical aberration. His idea, which he called wavefront reconstruction, was to record the diffraction pattern of an electron wave and then reconstruct a corrected image optically. A patent was filed in December 1947 and the work was published in Nature in 1948. Gabor's original arrangement, now called in-line or Gabor holography, placed the object, the recording plate, and the light source on a single axis. It suffered from the twin-image problem: the reconstructed real image was overlaid by an out-of-focus conjugate (virtual) image travelling along the same line of sight, which degraded the result.

Because Gabor had no coherent light source, he used a filtered high-pressure mercury lamp with a roughly 3 micrometre pinhole to obtain spatial coherence, which limited him to holograms about 1 cm across with exposures of several minutes. Optical holography did not advance significantly until the invention of the laser in 1960, which provided the bright, coherent light the technique requires.

In 1962, Emmett Leith and Juris Upatnieks at the University of Michigan recorded the first practical optical holograms of three-dimensional objects. Their off-axis (also called side-band) method introduced the reference beam at an angle, which separated the twin images so that a clear reconstruction could be viewed, solving the central limitation of Gabor's in-line scheme. Also in 1962, working independently in the Soviet Union, Yuri Denisyuk developed reflection holography, in which the hologram can be reconstructed in ordinary white light rather than laser light. In 1968 Stephen Benton, then at the Polaroid Corporation and later at the Massachusetts Institute of Technology, invented the rainbow (Benton) hologram, a transmission hologram designed to be viewed in white light; the recording uses a horizontal slit that removes vertical parallax to suppress the colour blur that white light would otherwise cause. Because rainbow holograms can be embossed and mass-produced, they became the basis for the security holograms on credit cards and banknotes. Gabor was awarded the Nobel Prize in Physics in 1971 for the invention.

How it works

Holography is an interferometric and diffractive process carried out in two stages, recording and reconstruction.

During recording, coherent light, in practice a laser, is split into two beams. The object beam illuminates the subject and the light it scatters travels to the recording medium. The reference beam is sent directly to the same medium. Where the two beams overlap they interfere, producing a fine pattern of bright and dark fringes whose spacing and shape encode both the amplitude and the phase of the object wave. This pattern is recorded on a photographic emulsion, photopolymer, or other medium and looks like meaningless speckle to the naked eye.

During reconstruction, the developed hologram is illuminated with light similar to the original reference beam. The recorded fringe pattern behaves as a complex diffraction grating and diffracts the illuminating light so as to recreate the original object wavefront. An observer looking into this reconstructed wavefront sees a three-dimensional image that shows parallax and changes with viewing angle, because the eye receives the same light field the object would have produced. This is the property that distinguishes a hologram from a stereoscopic display: a hologram presents a continuous light field, so the eye focuses (accommodates) on points at their true depth, whereas a stereoscopic display shows two flat images on a fixed screen plane.

Computer-generated holography

A hologram does not have to be made by physically interfering two light beams. In computer-generated holography (CGH) the interference pattern is calculated numerically from a digital model of the desired scene and then displayed, most often on a spatial light modulator (SLM), a pixelated device that modulates the phase or amplitude of light passing through or reflecting off it. Coherent light directed at the SLM is diffracted by the computed pattern to reconstruct the modelled wavefront, which means the displayed image can be changed electronically and animated. CGH is computationally demanding because each frame requires solving for the phase of every pixel, and the available space-bandwidth product of current SLMs limits image size and viewing angle. Modern research uses machine-learning methods to compute high-quality holograms in real time and to correct for optical imperfections in the display itself.

Relationship to AR and VR

The term "holographic" appears throughout AR and VR marketing, but it covers two different things that are easy to confuse.

Holographic optics in AR headsets

Many AR headsets and smart glasses use a holographic optical element (HOE) as part of their see-through optics. An HOE is itself a hologram, often a thin volume hologram recorded in a photopolymer, that acts as a wavelength-selective mirror, lens, or grating. In a waveguide display, a pair of such holographic gratings couples light from a small microdisplay into a transparent lens, guides it across the lens by total internal reflection, and then couples it back out toward the eye, so the user sees the projected image superimposed on the real world. Here the hologram is a passive optical component inside the lens; the image the user sees is still a conventional, mostly stereoscopic picture. The Denver-area startup Akonia Holographics, which described its product as volume holographic reflective and waveguide optics for transparent smart-glasses displays, was acquired by Apple in August 2018, a sign of how central holographic optics had become to AR headset development.

The "hologram" misnomer

The virtual objects that headsets such as the Microsoft HoloLens place in the user's environment are commonly called holograms, but they are not holograms in the physical sense. They are produced by real-time head-tracked stereoscopic rendering, the same principle used by VR headsets, in which two flat perspective images are shown to the two eyes. The holographic part of the HoloLens is the volume-hologram waveguide inside its lenses, not the floating image the wearer perceives. Because a stereoscopic image is fixed at one focal plane while the eyes converge on objects at varying apparent distances, such displays produce the vergence-accommodation conflict, a mismatch between where the eyes focus and where they converge that can cause eye strain. True holographic and light field displays are studied partly because they can present correct focus cues and avoid this conflict.

Holographic displays for AR and VR

A separate line of work aims to use real holography, usually computer-generated, as the actual display in a headset, so that virtual content is reconstructed as a true light field with continuous depth. In May 2024 a team at the Stanford Computational Imaging Lab led by Gordon Wetzstein published in Nature a full-colour 3D holographic AR display that pairs inverse-designed metasurface waveguide gratings with an AI-driven CGH algorithm and a phase SLM, fitting the optics into a glasses-like prototype that overlays full-colour three-dimensional images on the real world. The British company VividQ, founded in Cambridge in 2017, develops CGH display software and, with the waveguide maker Dispelix, announced in January 2023 a 3D waveguide combiner intended to show variable-depth holographic content in AR glasses while reducing the vergence-accommodation conflict; the company raised further funding in 2024 and continued to demonstrate the technology with game integrations through 2025. These holographic approaches differ from light field display devices such as the Looking Glass Portrait, which create a glasses-free 3D image by emitting many discrete views rather than by reconstructing a wavefront through diffraction.

Current status

As of 2026, optical holograms in the form of holographic optical elements and waveguide combiners are in widespread commercial use inside AR headsets and smart glasses, while full holographic displays for near-eye AR and VR remain largely in research and early prototype stages. The main obstacles are the limited resolution and space-bandwidth product of available spatial light modulators, the heavy computation required to generate holograms at video rates, and the difficulty of delivering a wide field of view and an adequate eyebox in a wearable form factor. Work since 2024 has concentrated on AI-accelerated hologram computation, metasurface and waveguide optics that shrink the hardware, and better colour and occlusion handling, with the goal of a thin, all-day-wearable display that reproduces true depth.