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## DMD Holographic display with extended reconstruction depth and LED illumination

### Maciej Józef Gruza

#### Abstract

The aim of this thesis is development of a holographic display based on a single Digital Micromirror Device (DMD) and an incoherent LED illumination. In past years researchers have proposed many display setups of holographic displays, most of them were based on liquid crystal spatial light modulators and coherent light source. DMD (Digital Micromirror Device) is a binary spatial light modulator. Because of its high speed it is possible to implement time multiplexing methods for hologram reconstruction. Due to pixel constructruction, DMD works as a blazed grating and resulting dispersion decreases quality of reconstruction. Laser as a light source provides the highest resolution of reconstructed holograms, but is bonded with a high contrast speckle noise and may cause eye hazard. Those negative effects can be mitigated by using incoherent LED source, which limits depth and resolution of the holographic display. First step was to generate binary holograms of specially designed resolution test by using Matlab software. Numerical reconstruction indicated the highest quality of reconstruction for histogram based binarization method with additional time multiplexing method. This allows to reduce noise and provides uniform intensity distribution of reconstructed images. Optical reconstruction of holograms showed negative effects of using DMD as a light modulator with LED illumination. Quality of reconstructed holograms decreases with distance from the modulator plane. For reconstruction distance larger than 20 mm, images were completely blurred. Possibility for quality improvement was investigated by increasing temporal coherence of light source with use of a spectral filter. After limiting the LED spectrum reconstruction depth increased to 50 mm. Because most of the light source energy was filtered out, thus the reconstructions were hardly visible. Proposed method of improving quality of reconstruction required examination of DMD modulator dispersion in order to minimize its effect. Correcting dispersion involved introduction to the system additional diffractive element, for example, a transmission grating, which provided dispersion with the same value, but with opposite sign. After numerical simulation of DMD dispersion for specific light source, parameters of diffraction grating were calculated. From gratings available in the laboratory, the best possible dispersion correction would be achieved for 860 grooves/mm grating, with illumination angle equal 30°. That would provide illumination of DMD surface with the first order of diffracted beam. Diffraction grating used in the holographic display setup extended reconstruction depth up to 70 mm, with satisfying quality of reconstructed holograms. These results were not achievable with the previous display setup. Proposed approach with use of diffraction grating is free of the negative effects of using spectral filter and provides better energy distribution. Proposed grating and setup is designed for specific light source, but it is possible to use it with other color LED light sources by adjusting illumination angle and grating setup for different wavelength.
Diploma type
Engineer's / Bachelor of Science
Diploma type
Engineer's thesis
Author
Maciej Józef Gruza (FM) Maciej Józef Gruza,, Faculty of Mechatronics (FM)
Title in Polish
Wyświetlacz holograficzny bazujący na modulatorze DMD i oświetleniu LED z rozszerzoną głębią rekonstrukcji
Supervisor
Tomasz Kozacki (FM/IMPh) Tomasz Kozacki,, The Institute of Micromechanics and Photonics (FM/IMPh)Faculty of Mechatronics (FM)
Certifying unit
Faculty of Mechatronics (FM)
Affiliation unit
The Institute of Micromechanics and Photonics (FM/IMPh)
Study subject / specialization
, Mechatronika
Language
(pl) Polish
Status
Finished
Defense Date
29-05-2019
Issue date (year)
2019
Reviewers
Tomasz Kozacki (FM/IMPh) Tomasz Kozacki,, The Institute of Micromechanics and Photonics (FM/IMPh)Faculty of Mechatronics (FM) Julianna Winnik (FM/IMPh) Julianna Winnik,, The Institute of Micromechanics and Photonics (FM/IMPh)Faculty of Mechatronics (FM)
Keywords in Polish
holografia, modulatory światła, wyświetlacze holograficzne.
Keywords in English
holography, light modulators, holographic displays.
Abstract in Polish
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Identyfikator pracy APD: 34054

Uniform Resource Identifier
https://repo.pw.edu.pl/info/bachelor/WUT05fa1b2ef00b481891fcc1e7446d3410/
URN
urn:pw-repo:WUT05fa1b2ef00b481891fcc1e7446d3410

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