Herein, we develop an adhesive-free double-faced nanotransfer
lithography (ADNT) technique based on the surface deformation of flexible
substrates under the conditions of temperature and pressure control
and thus address the challenge of realizing the mass production of
large-area nanodevices in the fields of optics, metasurfaces, and
holograms. During ADNT, which is conducted on a flexible polymer substrate
above its glass transition temperature in the absence of adhesive
materials and chemical bonding agents, nanostructures from the polymer
stamp are attached to the deformed polymer substrate. Various silicon
masters are employed to prove our method applicable to arbitrary nanopatterns,
and diverse Ag and Au nanostructures are deposited on polymer molds
to demonstrate the wide scope of useable metals. Finally, ADNT is
used to (i) produce a flexible large-area hologram on the defect-free
poly(methyl methacrylate) (PMMA) film and (ii) fabricate a metasurface
hologram and a color filter on the front and back surfaces of the
PMMA film, respectively, to realize dual functionality. Thus, it is
concluded that the use of ADNT can decrease the fabrication time and
cost of high-density nanodevices and facilitate their commercialization.
The coherence of a light source is a vital aspect regarding the image quality of holographic contents. Generally, the coherence of the light source is the reason for speckle noise in a holographic display, which degrades the image quality. To reduce the speckle noise, partially coherent light sources such as light-emitting diodes (LED) have been studied. However, if the coherence of the light source is too low, the reconstructed image will blur. Therefore, using a spatial filter to improve the spatial coherence of LEDs has been proposed. In this study, we analyze the effect of the spatial and temporal coherence of the LED light source in a digital holographic display, and the optimal spatial coherence is determined. For this purpose, we devised an optical structure to control the spatial coherence in a holographic display system using a digital micro-mirror device (DMD). Here, the DMD functions as a dynamic spatial filter. By evaluating the change in the holographic image quality according to the spatial filter size, we obtained an optimal spatial filter size of 270 µm in our system. The proposed method is expected to be useful for selecting the optimal coherence of the light source for holographic displays.
An efficient synthesis algorithm for wide-viewing full-color depthmap computer-generated holograms is proposed. We develop a precise computational algorithm integrating wave-optic geometry-mapping, color-matching, and noise-filtering to multiplex multiview elementary computer-generated holograms (CGHs) into a single high-definition CGH without three-dimensional perspective distortion or color dispersion. Computational parallelism is exploited to achieve significant computational efficiency improvement in the production throughput of full-color wide-viewing angle CGHs. The proposed algorithm is verified through the full-color binary hologram reconstruction experiments utilizing an off-axis R·G·B simultaneous illumination method, which suggests the feasibility of the full-color sub-wavelength binary spatial light modulator technology.
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