Liquid crystal microlens arrays recorded by polarization holography

Abstract

We report the characterization of diffractive microlens arrays (MAs) using a polarization holographic approach assisted by a spatial light modulator (SLM), in a nematic liquid crystal (NLC) cell. The MAs were recorded in the photoaligning substrates of the cell and then replicated in the NLC bulk, through the surface interactions. The transparency of the NLC on a wide range of wavelengths and the ability to tune its optical birefringence, through an external voltage, allowed us to create MAs with high efficiency. We have presented the results obtained for diverse MAs configurations, composed by spherical and cylindrical microlenses and characterized by different focal lengths. The efficiency reaches a value of 90%, at a wavelength of 633 nm.

Switchable 3D liquid crystal grating generated by periodic photo-alignment on both substrates

“…Liquid crystals (LCs) are widely used in display applications and their unique electro-optic properties also make them suitable for the use in photonic components such as optical filters, switches, beam-steering devices, spatial light modulators, lasers, and optical nonlinear components. [1][2][3][4][5][6][7][8] Multiple techniques such as mechanical rubbing, ion beam etching and oblique deposition of inorganic material have been investigated in the past to control the LC alignment near the surface. Photo-alignment materials recently gained popularity thanks to the flexibility to align liquid crystals in complex configurations that cannot be obtained with common alignment techniques.…”

Low f‐Number Diffraction‐Limited Pancharatnam–Berry Microlenses Enabled by Plasmonic Photopatterning of Liquid Crystal Polymers

“…However, to achieve high performances, very complex fabrication processes are needed. [13,14,21,[29][30][31][32][33][34] The PB microlenses made of liquid crystals are particularly attractive because of their close to 100% efficiency and switchable focal lengths. [19,[24][25][26] The phase profiles desired for lensing can also be realized with the Pancharatnam-Berry (PB) phases [27,28] by using birefringent materials or metasurfaces with spatially variant optical axes.…”

“…For example, up to 8 lithography steps and sometimes electron-beam lithography are needed to achieve low f-numbers, [21][22][23] diffraction-limited performance, and over 90% efficiency. [31,33,35,36] Large-sized PB lenses with low f-numbers can be made by holography photopatterning with a refractive master lens, [31] while liquid crystal PB microlenses are still limited to large f-number (>10) [32,33] and no work has been able to show diffraction-limited quality.A range of techniques have been developed in recent years to align liquid crystal molecules into arbitrary designer orientation patterns, which are either based on photoalignments using digital micromirror device (DMD), [37,38] pixel-to-pixel direct laser writing, [30] holography interference [31] and plasmonic photo patterning, [39][40][41] or based on nanostructured surfaces by using nanoimprinting [33] or atomic force microscopy scribing. [13,14,21,[29][30][31][32][33][34] The PB microlenses made of liquid crystals are particularly attractive because of their close to 100% efficiency and switchable focal lengths.…”

“…For example, up to 8 lithography steps and sometimes electron-beam lithography are needed to achieve low f-numbers, [21][22][23] diffraction-limited performance, and over 90% efficiency. [31,33,35,36] Large-sized PB lenses with low f-numbers can be made by holography photopatterning with a refractive master lens, [31] while liquid crystal PB microlenses are still limited to large f-number (>10) [32,33] and no work has been able to show diffraction-limited quality. [13,14,21,[29][30][31][32][33][34] The PB microlenses made of liquid crystals are particularly attractive because of their close to 100% efficiency and switchable focal lengths.…”

Surface Stabilized Topological Solitons in Nematic Liquid Crystals

“…This has been successfully applied to create very efficient transmissive and reflective LC flat-optics devices, that are manipulating the so-called geometric (or Pancharatnam-Berry) phase of light. Micrometer thin optical components (such as microlens arrays, beam shaping elements and polarization gratings) with close to 100% efficiency were demonstrated in this way and high-quality vortex beams and vector beams were generated [6][7][8][9][17][18][19][20]. Photo-aligned LC samples can also be applied to steer the placement of 2 of 17 micro-particles, to control active matter (influence bacterial movement) and to make stimuli-responsive soft actuators [1][2][3][4][5].…”