Andrii B. Golovin

Fast Switching Dual-Frequency Liquid Crystal Optical Retarder, Driven by an Amplitude and Frequency Modulated Voltage

We demonstrate theoretically and experimentally a fast-switching nematic optical retarder capable to switch a few microns of optical retardation in less than 1 ms. For example, a nematic cell of thickness 14.5 μm switches 0.3 μm of retardation within 0.15 ms and 2.5 μm within 0.5 ms for single passage of beam. The corresponding figure of merit is two orders of magnitude higher than the one known for the best nematic materials synthesized so far. The fit is achieved by employing a dual-frequency nematic liquid crystal in high-pretilt angle cells and a special addressing scheme that features amplitude and frequency modulated voltage. The scheme can be used in spatial light modulators, retarders, beam deflectors, polarization rotator, and displays.

Electrically reconfigurable optical metamaterial based on colloidal dispersion of metal nanorods in dielectric fluid

Optical metamaterials capture the imagination with breathtaking promises of nanoscale resolution in imaging and invisibility cloaking. We demonstrate an approach to construct a metamaterial in which metallic nanorods, of dimension much smaller than the wavelength of light, are suspended in a fluid and placed in a nonuniform electric field. The field controls the spatial distribution and orientation of nanorods because of the dielectrophoretic effect. The field-controlled placement of nanorods causes optical effects such as varying refractive index, optical anisotropy (birefringence), and reduced visibility of an object enclosed by the metamaterial.

Lyotropic chromonic liquid crystal semiconductors for water-solution processable organic electronics

We propose lyotropic chromonic liquid crystals (LCLCs) as a distinct class of materials for organic electronics. In water, the chromonic molecules stack on top of each other into elongated aggregates that form orientationally ordered phases. The aligned aggregated structure is preserved when the material is deposited onto a substrate and dried. The dried LCLC films show a strongly anisotropic electric conductivity of semiconductor type. The field-effect carrier mobility measured along the molecular aggregates in unoptimized films of LCLC V20 is 0.03 cm^2 V^(-1) s^(-1). Easy processibility, low cost, and high mobility demonstrate the potential of LCLCs for microelectronic applications.

FAST SWITCHING OPTICAL MODULATOR BASED ON DUAL FREQUENCY NEMATIC CELL

We demonstrate a fast optical modulator capable of switching large amount of optical retardation(a few microns)in less than 1 ms. The result is achieved by employing a dual frequency nematic in cells with high pre-tilt alignment and by providing a special addressing scheme that features amplitude and frequency modulated voltage. We explore the effect of surface alignment and dielectric heating on the switching time. We also report the measurements of dielectric permittivities and crossover frequency of dual frequency nematic.

Electro-Optic Effects in Colloidal Dispersion of Metal Nano-Rods in Dielectric Fluid

In modern transformation optics, one explores metamaterials with properties that vary from point to point in space and time, suitable for application in devices such as an “optical invisibility cloak” and an “optical black hole”. We propose an approach to construct spatially varying and switchable metamaterials that are based on colloidal dispersions of metal nano-rods (NRs) in dielectric fluids, in which dielectrophoretic forces, originating in the electric field gradients, create spatially varying configurations of aligned NRs. The electric field controls orientation and concentration of NRs and thus modulates the optical properties of the medium. Using gold (Au) NRs dispersed in toluene, we demonstrate electrically induced change in refractive index on the order of 0.1.

Lyotropic chromonic liquid crystals in aligned films for applications as polarizing coatings

Abstract We describe dried oriented films with anisotropic structural and optical properties prepared from the aqueous solutions of plank‐like molecules, the so‐called Lyotropic Chromonic Liquid Crystals (LCLCs). The dried LCLC films may be used as optical elements, such as polarizers, compensators, color filters, or retardation plates in the UV, visible, or infrared parts of spectrums. The optical quality of the films is determined by the uniformity of the molecular alignment, which often distorted by periodic variations of the director field. We describe different ways to improve the alignment properties of the films by using additives. We present compositions capable of polarizing effects in visible and UV parts of spectrum.

Photon sorting in the near field using subwavelength cavity arrays in the near-infrared

A frequency selective metasurface capable of sorting photons in the near-infrared spectral range is designed, fabricated, and characterized. The metasurface, a periodic array of dielectric cylindrical cavities in a gold film, localizes and transmits light of two spectral frequency bands into spatially separated cavities, resulting in near-field light splitting. The design and fabrication methodologies of the metasurface are discussed. The transmittance and photon sorting properties of the designed structure is simulated numerically and the measured transmission is presented.

55.2: Fast Switching Dual‐Frequency Liquid Crystal Optical Retarder, Driven by an Amplitude and Frequency Modulated Voltage

We employed amplitude and frequency modulated voltage in fast switching optical retarder with a high pretilt angle dual-frequency nematic cell. We obtained the response times 150 − 500 μs for an optical retardation shift on 0.3 − 2.2 μm in optical retarder with 12 μm thick nematic cell. The results could be used in beam steering, adaptive optics and display devices.

Electrically reconfigurable optical metamaterials based on orientationally ordered dispersions of metal nano-rods in dielectric fluids

Optical metamaterials capture the imagination with potential applications such as sub-wave imaging, invisibility cloaking and solar energy collection. The challenge is to learn how to construct and reconfigure a metamaterial with a spatially varying refractive index. We describe an approach based on colloidal dispersion of metal nano-rods in a dielectric fluid placed in a non-uniform electric field. Because of the dielectrophoretic effect, the nano-rods accumulate in the regions with the maximum field and align along the field lines. High concentration of nano-rods lowers the effective local refractive index of the dispersion. The nano-rods are much smaller than the wavelength of light. We illustrate the approach with a dispersion of gold nanorods (length 40-70 nm, diameter 10-20 nm) in toluene, using flat and cylindrical cells. In the first case, the electric field is created by two mutually perpendicular electrodes, in the second case, it is created by two coaxial electrodes. When the field is applied, the initially isotropic dispersion of nanorods transforms into birefringent orientationally ordered structures with the director following the electric field lines. We describe how the optical properties of the field-induced structures are controlled by dichroism and birefringence of the dispersion and determine the spatial variation of the field-induced optical phase retardation. In cylindrical capillaries, the index gradient bends lights around the central electrode, thus reducing its visibility. Our approach can be used as a starting point for the development of self-assembled and reconfigurable optical metamaterials with optical properties controlled by the dielectrophoretic effect on submicron scales.

Achromatic linear polarization switch for visible and near infrared radiation based on dual-frequency twisted nematic cell

We developed a broad band achromatic linear polarization switch for visible and near infrared radiation. The achromatic switch is based on a twisted nematic cell filled with a dual-frequency nematic material. The switch is capable of fast switching linearly polarized light between two orthogonal directions with a switching time in the millisecond range.