Converging Microlens Array Using Nematic Liquid Crystals Doped with Chiral Nanoparticles

Abstract

Nematic liquid crystals of achiral molecules or racemic mixtures of chiral ones form flat films when suspended in submillimeter size grids and submerged under water. Recently, it has been shown (Popov et al., 2017) that films of nematic liquid crystals doped with chiral molecules adopt biconvex lens shapes underwater. The curved shape together with degenerate planar anchoring leads to a radial variation of the optical axis along the plane of the film, providing a Pancharatnam–Berry-type phase lens that modifies geometric optical imaging. Here, we describe nematic liquid crystal microlenses formed by the addition of chiral nanoparticles. It is found that the helical twisting power of the nanoparticles, the key factor to form the lens, is about 400 μm–1, greater than that of the strongest molecular chiral dopants. We demonstrate imaging capabilities and measure the shape as well as the focal length of the chiral nanoparticle-doped liquid crystal lens. We show that measuring the shape of the lens allows one to calculate the helical pitch of the chiral nematic liquid crystal and thus determine the helical twisting power of the chiral ligand-capped nanoparticles. Such measurements require the use of only nanograms of chiral nanoparticles, which is 3 orders of magnitude less than that required by conventional techniques. Since NPs are sensitive to external stimuli such as light and electric and magnetic fields, the use of chiral NPs may allow the achievement of tunable optical properties for such microlens arrays.

Liquid crystal-templated chiral nanomaterials: from chiral plasmonics to circularly polarized luminescence

“…The chiral plasmonic nanomaterials could also exhibit larger chiral correlation lengths, long-range interactions between chiral molecules and plasmonic nanomaterials, and enhanced g-factor for chiral molecules in the vicinity of plasmonic nanomaterials [177][178][179] . Interestingly, an array biconvex converging microlens with robust imaging capabilities has been fabricated using liquid crystal-templated chiral plasmonic nanomaterials 180 .…”

Polymer Stabilized Paraboloid Liquid Crystal Microlenses with Integrated Pancharatnam–Berry Phase

“…Note, similar behavior was also observed for biconvex chiral LC lenses formed underwater and found to be a combination of geometric and PB phase lenses. [31,32]…”

“…One may estimate the variation of the optical axis from the center to the boundary as β = π/2 for the achiral mixture and as β = 2πΔD/p for the chiral mixtures, [31] where ΔD is the change of the lens thickness between the boundary and center and p is the pitch of the helix (p(2%) = 6 μm, p(4%) = 3 μm and p(6%) = 2 μm). However, more quantitative analysis is pointless, since we do not know either the exact spatial variation of the refractive index, or of the optical axis.…”

“…In this paper, we describe fabrication of plano-concave nematic LC microlens arrays where the individual lenses have embedded GRIN and PB phase [30][31][32] in addition to their paraboloid shapes. The paraboloid shapes are formed as a result Aspheric lenses reduce aberration and provide sharper images with improved spot size compared to spherical lenses.…”

Self-assembled liquid crystal architectures for soft matter photonics

“…They further demonstrated switchable chromatic aberration by applying a bias voltage for different purposes. CLC is also a kind of popular soft material in lens fabrications 218 – 220 . A PB phase lenticular microlens with a polarization-dependent focal length by immersing chiral gold nanoparticles doped CLCs in water was reported by Perera et al 220 , Fig.…”