Holographic Displays (HDs) provide 3D images with all natural depth cuesvia computer generated holograms (CGHs) implemented on spatial lightmodulators (SLMs). HDs are coherent light processing systems based oninterference and diffraction, thus they generally use laser light.However, laser sources are relatively expensive, available only at someparticular wavelengths and difficult to miniaturize. In addition, highlycoherent nature of laser light makes some undesired visual effects quiteevident, such as speckle noise, interference due to stray light ordefects of optical components. On the other hand, LED sources areavailable in variety of wavelengths, has small die size, and no speckleartifact. However, their finite spatial size introduce some degree ofspatial incoherence in an HD system and degrade image resolution, whichis the subject of the study in this paper. Our theoretical analysisindicates that the amount of resolution loss depends on the distancebetween hologram and SLM image planes. For some special configurations,the source size has no effect at all. We also performed experiments withdifferent configurations using lasers and LEDs with different emissionareas that vary from 50 μm to 200 μm, and determined Contrast TransferFunction (CTF) curves which agree well with our theoretical model. Theresults show that it is possible to find configurations where LEDscombined with pinholes almost preserve natural resolution limit of humaneye while keeping the loss in light efficiency within tolerable limits.

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10126/1/Effect-of-spatial-coherence-of-LED-sources-on-image-resolution/10.1117/12.2252413.full

V. P. Ghoushchi, M. Aas, E. Ulusoya, and H. Ürey

2017

02/2017

Proc. of SPIE

10126

101260A-1

3D displays, 3D image reconstruction, computer generated holography, Holograms, Holography, Image resolution, laser sources, LED displays, Light-emitting diodes, Spatial coherence, speckle