Far-field and Fresnel Liquid Crystal Geometric Phase Holograms via Direct-Write Photo-Alignment

Abstract

Abstract:We study computer-generated geometric-phase holograms (GPHs) realized by photo-aligned liquid crystals, in both simulation and experiment. We demonstrate both far-field and Fresnel holograms capable of producing far-field and near-field images with preserved fidelity for all wavelengths. The GPHs are fabricated by patterning a photo-alignment layer (PAL) using a direct-write laser scanner and coating the surface with a polymerizable liquid crystal (i.e., a reactive mesogen). We study various recording pixel sizes, down to 3 µm, that are easily recorded in the PAL. We characterize the fabricated elements and find good agreement with theory and numerical simulation. Because of the wavelength independent geometric phase, the (phase) fidelity of the replay images is preserved for all wavelengths, unlike conventional dynamic phase holograms. However, governed by the diffraction equation, the size and location of a reconstructed image depends on the replay wavelength for far-field and near-field GPHs, respectively. These offer interesting opportunities for white-light holography.

Multi-color holography with a two-stage patterned liquid-crystal element

“…In addition, there is a non-zero background with speckles that is not part of the structures. This background should not be attributed to the scattering of the liquid-crystal film [21], but rather, to the hologram phase design. In this design the hologram has a background that is only suppressed by a factor of 100, and can still be seen by the camera.…”

“…As discussed above, GPHs are efficient over a large bandwidth and apply wavelength-independent geometric phase shifts [21]. However, they have so far not been used much for multi-color holography as they are diffractive, generating wavelength scaled holograms.…”

“…The many degrees of freedom of these multi-twist retarder (MTR) films may be used to tune the retardation of the LC layer to half-wave retardance, achieving high efficiency [6,7] in GPHs over large bandwidths into a single diffracted order. Furthermore, GPHs are ideal to record CGHs as they can be manufactured with unbounded continuous phase, wide angular bandwidths, and very high spatial frequencies [21][22][23].…”

“…This is common for all GPHs. A computer generated Fraunhofer CGH will therefore have the same intensity distribution for all wavelengths, only wavelength-scaled [21]. Note that CGHs created with dynamic phase elements, i.e., produced by locally changing the optical path length, have decreased fidelity for wavelengths than other than the one the pattern was optimized for.…”

Application of Dimming Compensation Technology Via Liquid Crystal Lens for Non-Imaging Projection Laser Systems

“…The liquid crystal lens [5][6][7][8][9][10][11] is a type of microlens component that has been developed in recent years. The zooming principle is mainly based on applying an external electric field to drive the rotation of the liquid crystal molecules and present a gradient arrangement with an appropriate direction in the liquid crystal layer.…”