Optical chirality is intrinsically weak, and hard to tune in traditional bottom-up chiral perovskites. Here we realized all-dielectric halide perovskite chiral metasurfaces with a giant circular dichroism of 70% via high-throughput screening. Combining the giant optical chirality, unique light emission property and simple low-temperature solution processing technique, perovskite chiral metasurface paves the way towards real application in chiroptoelectronic and chiro-spintronic devices.
We develop a new approach for creating photonic metasurfaces based on nematic liquid crystal material. The periodical modulation of the LC director field is imposed by nanoscale change of the alignment properties of polyimide thin layer by means of focused ion beam treatment. The resulted spatially periodic modulation with a period determined by that of the pattern at the substrate provides distinct photonic properties of LC layer. A part of transmitted light is redistributed into a few first diffraction orders. The diffraction is switchable by electric field with millisecond switching times.
Two electrooptical effects in a system consisting of subwavelength aluminum gratings and a nematic liquid crystal (LC)
layer are discussed. The aluminum gratings produced by a focused ion beam lithography act as interdigitated electrodes,
which allows application of an electric field to a very thin fraction of LC layer contacting the grating. The first of the
electrooptical effects is associated with an enhanced TE-polarized light transmission of the gratings and the surface
induced twist deformation in the bulk of the LC layer, whereas the second one is caused by an influence of the
electrically driven LC surface layer on the plasmonic resonance and the related dip of the TM-polarized grating
transmission. Besides the different polarizations, the two effects have dramatically different response times. In the case
of the plasmonic effect, the measured response time is found to be of 20 - 30 microseconds that is three orders of
magnitude faster compared to the switching based on the surface induced twist effect.
Metamaterials with high optical activity (OA) and circular dichroism (CD) are desired for various prospective applications ranging from circular light polarizing to enhanced chiral sensing and biosensing. Modern techniques allow fabricating subwavelength arrays of holes of complex chiral shapes that exhibit extreme optical chirality: their OA and CD take the whole range of possible values in the visible. In order to understand the nature of extreme chirality, we performed the electromagnetic finite difference time domain simulations for the hole shapes resolved by atomic force microscopy. The analysis of the simulation data allowed us to develop an analytical chiral coupled-mode model that nicely fits the results and explains the extreme chirality as determined by the Fano-type transmission resonance due to the interference of a weak background channel and a resonant plasmon channel. The model shows critical importance of the dissipation losses, the hole shape symmetry and chirality. In a planar 2D-chiral hole array, the mirror asymmetry can be induced by the difference of dielectric materials adjacent to the array sides and even their weak deviation results in remarkably strong OA and CD. We note that such deviations can arise due to the dielectric nonlinearity and discuss how 2D-chiral metamaterials in symmetric environment can acquire optical chirality due to the nonlinear symmetry breaking.
We discuss a novel tuning method based on continuous adjustment of metamaterial lattice parameters. This
method provides for remarkable tuning of transmission characteristics through a subtle displacement of metamaterial
layers. While the effective medium theory predicts correctly the general tuning characteristics, it turns
out that the particular tuning pattern is determined by the peculiarities of near-field interaction between the
metamaterial elements. We describe the modes of this interaction and provide qualitative explanations to the
performance observed numerically and experimentally.
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