Digital holography is a way to register 3D information using digital cameras. Today it already has wide practical application, and in the future, scientists are sure, will be indispensable in a number of areas, from medicine to astronomy. About the present and future of digital holography.
Physical principles of holography
Holography is a method that allows you to register information about an object and restore its image, including in a three-dimensional form. This is achieved by registering not only the amplitude of the light (as in standard photography), but also the phase, which makes it possible to observe the image reconstructed from the hologram from various angles.
Holograms are recorded by registering the total amplitude of two light beams: an object (reflected from an object or transmitted through it) and a reference one. If they are coherent with each other - they have a constant phase difference - then an interference pattern is formed in the plane of overlapping beams, which is recorded by digital photosensors or photosensitive media.
World trends
Using digital holography, you can create real three-dimensional visualization of objects and scenes. This does not require special glasses for observing scenes or special positioning of the observer. On this principle, 3D displays are now being actively developed, which allow visualizing high-quality images. As scientists are sure, the moment is approaching when color images from holograms will be similar in color quality to photographs, while reproducing a three-dimensional image of an object.
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One of the current advances is 5G communication using holographic principles to create an image of the interlocutor. Experts believe that in a few years time this technology will be able to become a commercial service.
An extremely promising direction is 3D printing using holograms. The holographic image of the part is divided by sections into projections and then, under program control, a fast layer-by-layer printing of each projection is carried out.
The areas of digital holography that are used in scientific and applied research are actively developing: holographic microscopy (visualization of micro- and nano-objects) and holographic interferometry (dynamic registration of changes in object parameters - temperature, shape, refractive index).
In addition, digital holography is already widely used in medical and biological imaging, in systems for coding, transmission and storage of data, and also makes it possible to increase the security of products, banknotes and bank cards.
Russian achievements
Today, research in the field of holography - both analog and digital - is carried out by a number of universities and companies whose laboratories have achieved significant results.
For example, NRNU MEPhI has implemented a system for dynamic recording, transmission and real-time optical demonstration of holograms with a resolution of at least 2 million pixels. It allows you to remotely reproduce scenes and objects recorded in both the optical and infrared ranges - which can be used, for example, to record information in aggressive environments.
Today, for the transmission of holographic video, a channel with a bandwidth of at least units of gigabits per second is required; therefore, technologies for converting and compressing digital holograms are of great importance. NRNU MEPhI is actively working in this direction. In May 2019, the Scientific Reports magazine presented a method for compressing holographic information hundreds of times, developed within the framework of the Russian Science Foundation grant No. 18-79-00277.
Another important area is improving the quality of optical display of 3D scenes from recorded holograms. The Institute of Laser and Plasma Technologies (LaPlaz) of NRNU MEPhI develops methods for improving computer and real optical display of holograms using multi-gradation liquid crystal and binary high-speed micromirror light modulators. In 2019, scientists from NRNU MEPhI published a large-scale study of binarization methods for displaying 3D objects in the best quality in the OpticsandLasersinEngineering journal. As the scientists explained, this development could be useful in creating high-speed 3D displays.
Holography is applicable not only for storing, but also for protecting information. Scientists at NRNU MEPhI are currently creating data coding systems using an image recorded on a hologram as a coding key. Within the framework of the Russian Science Foundation grant No. 19-19-00498, work is underway to create a coding system based on high-speed micromirror light modulators. Such a system is capable of encoding information at a bandwidth of gigabits per second.
An equally important area of research is object recognition. Today, as the specialists of NRNU MEPhI explained, recognition devices usually use only spatial features. In a recently published article in the journal Optics Communications, a method was proposed for recognition by both shape and spectral features, applicable, for example, in orientation devices in space or for identifying biological species.