Photonics Dictionary

computer-generated hologram

A computer-generated hologram (CGH) is a holographic image produced using computational methods and algorithms, rather than traditional optical techniques. CGHs are generated entirely in digital form using computers and are often displayed on devices such as liquid crystal displays (LCDs) or digital micro-mirror devices (DMDs).

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The process of creating a computer-generated hologram typically involves the following steps:

Scene representation: The scene or object to be holographically reconstructed is digitally modeled or captured using computer graphics techniques, 3D scanning, or other imaging methods.

Wavefront propagation: A numerical simulation of the light field emitted or scattered by the object is computed using wave optics principles. This involves calculating the propagation of light waves from each point on the object's surface to the hologram plane.

Hologram calculation: Based on the wavefront data, algorithms are used to compute the interference pattern or hologram that will reconstruct the desired image when illuminated with coherent light. Various mathematical techniques such as Fourier transforms, diffraction calculations, and iterative optimization methods may be employed in this step.

Hologram display: The computed hologram is displayed on a spatial light modulator (SLM) such as an LCD or DMD. The SLM modulates the phase or amplitude of incident light to reproduce the interference pattern encoded in the hologram.

Image reconstruction: When illuminated with coherent light, such as a laser beam, the SLM diffracts the light according to the hologram pattern. As the diffracted light propagates, it interferes with itself to reconstruct the original 3D scene, producing a holographic image that appears to

Computer-generated holograms offer several advantages over traditional holographic techniques, including greater flexibility in designing complex holographic scenes, easier manipulation of hologram parameters, and the ability to dynamically update or change holographic content in real time. They are used in a variety of applications, including holographic displays, security features, data storage, and artistic expression.
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