Parallel sorting of orbital and spin angular momenta of light in a record large number of channels.

Parallel sorting of orbital and spin angular momentum components of structured optical beams is demonstrated. Both spin channels are multiplexed within the novel orbital angular momentum (OAM) sorter, reducing the size, weight, and number of elements. The sorted states are linearly spaced over 70 topological charge values. We experimentally and theoretically evaluate the operational range and crosstalk between neighboring channels and find that 30 orbital angular momentum states are available per spin channel for quantum communication or cryptography. This is achieved using an angular momentum sorter that we developed based on geometric phase optical elements. We present two devices consisting of liquid crystal polymer films photoaligned with complex two-dimensional patterns.

Beam shaping diffractive wave plates [Invited].

We present and discuss opportunities opened up by a new generation of beam shaping optical elements that combine capabilities of digital spatial light polarization converters and diffractive properties of thin liquid crystalline films with patterned orientation of anisotropy axis (diffractive wave plates). Several functions of the new generation beam shapers are demonstrated, among them converting a laser beam of a Gaussian profile into a ring profile in the far field, a flattop profile, and into complex images. We also describe electrically controlled beam shaping optical elements which can be turned off and on within milliseconds by applying a low external voltage. Optical, morphological, and electro-optical properties of the components are characterized.

Electrically switchable diffractive waveplates with metasurface aligned liquid crystals.

Diffractive waveplates and equivalent metasurfaces provide a promising path for applications in thin film beam steering, tunable lenses, and polarization filters. However, fixed metasurfaces alone are unable to be tuned electronically. By combining metasurfaces with tunable liquid crystals, we experimentally demonstrate a single layer device capable of electrically switching a diffractive waveplate design at a measured peak diffraction efficiency of 35%, and a minimum switching voltage of 10V. Furthermore, the nano-scale metasurface aligned liquid crystals are largely independent of variations in wavelength and temperature. We also present a computational analysis of the efficiency limits of liquid crystal based diffractive waveplates, and compare this analysis to experimental measurements.

Digital polarization holography advancing geometrical phase optics.

Geometrical phase or the fourth generation (4G) optics enables realization of optical components (lenses, prisms, gratings, spiral phase plates, etc.) by patterning the optical axis orientation in the plane of thin anisotropic films. Such components exhibit near 100% diffraction efficiency over a broadband of wavelengths. The films are obtained by coating liquid crystalline (LC) materials over substrates with patterned alignment conditions. Photo-anisotropic materials are used for producing desired alignment conditions at the substrate surface. We present and discuss here an opportunity of producing the widest variety of "free-form" 4G optical components with arbitrary spatial patterns of the optical anisotropy axis orientation with the aid of a digital spatial light polarization converter (DSLPC). The DSLPC is based on a reflective, high resolution spatial light modulator (SLM) combined with an "ad hoc" optical setup. The most attractive feature of the use of a DSLPC for photoalignment of nanometer thin photo-anisotropic coatings is that the orientation of the alignment layer, and therefore of the fabricated LC or LC polymer (LCP) components can be specified on a pixel-by-pixel basis with high spatial resolution. By varying the optical magnification or de-magnification the spatial resolution of the photoaligned layer can be adjusted to an optimum for each application. With a simple "click" it is possible to record different optical components as well as arbitrary patterns ranging from lenses to invisible labels and other transparent labels that reveal different images depending on the side from which they are viewed.

Broadband waveplate lenses.

We report on lenses that operate over the visible wavelength band from 450 nm to beyond 700 nm, and other lenses that operate over a wide region in the near-infrared from 650 nm to beyond 1000 nm. Lenses were recorded in liquid crystal polymer layers only a few micrometers thick, using laser-based photoalignment and UV photopolymerization. Waveplate lenses allowed focusing and defocusing laser beams depending on the sign of the circularity of laser beam polarization. Diffraction efficiency of recorded waveplate lenses was up to 90% and contrast ratio was up to 500:1.

High contrast switching of transmission due to electrohydrodynamic effect in stacked thin systems of liquid crystals.

We study the opportunity of using electrohydrodynamic instabilities in a nematic liquid crystal mixture with negative dielectric anisotropy for controlling laser beams. Switching between naturally transparent and diffuse light scattering states is achieved by application of low frequency, low amplitude voltages. The specifics of diffuse light scattering state depending on the orientation and thickness of the liquid crystal layer are revealed. The switching occurs on a milliseconds time scale. Combination of thin, flexible liquid crystal cells allows polarization independent, high contrast, fast switching in a broad band of visible wavelengths.

Thin waveplate lenses of switchable focal length--new generation in optics.

We present new lenses - waveplate lenses created in liquid crystal and liquid crystal polymer materials. Using an electrically-switchable liquid-crystal half-wave retarder we realized switching between focused and defocused beams by the waveplate lens. A combination of two such lenses allowed the collimation of a laser beam as well as the change of focal length of optical system.

Tunable millimeter and sub-millimeter spectral response of textile metamaterial via resonant states.

We report on a new textile metamaterial created by adding metal wires directly into the polymer yarn. Split-ring resonator-like extended states are created. Simulations revealed that the extended states can be easily tuned via the geometry. Measurements of the transmittance spectrum as a function of the polarization angle in the low terahertz range were also performed and these peaks were ascribed to a polarization-dependent resonator model. The fabrics are viable candidates for flexible and deformable gigahertz and terahertz-enabled metamaterials.

Variable transmission lens influences on the dynamics of pupillary light reflexes.

This study examined the influence of liquid crystal variable transmission lenses on pupillary light reflexes in response to sudden bright light onset. Participants were exposed to bright light while pupil size was monitored using an eye tracker; eyewear was configured across four transition conditions: constant low-light filtering, constant high-light filtering, variable-light filtering in response to light detection and a control condition without eyewear. Before light onset, pupil diameter was largest in the high-filter condition, medium in the variable- and low-light filtering conditions and smallest in the control condition. Following light onset, the low-light filtering and control conditions, and the high-light filtering and variable-light filtering conditions converged over time. Critically, automatically transitioning between low- and high-light filtering reduced the magnitude (approximately 0.2 mm) and duration (approximately 360 ms) of the pupillary response relative to constant low-light filtering.

All-optical diffractive/transmissive switch based on coupled cycloidal diffractive waveplates.

Pairs of cycloidal diffractive waveplates can be used to doubly diffract or collinearly propagate laser radiation of the appropriate wavelength. The use of a dynamic phase retarder placed in between the pair can be utilized to switch between the two optical states. We present results from the implementation of an azo-based retarder whose optical properties can be modulated using light itself. We show fast and efficient switching between the two states for both CW and single nanosecond laser pulses of green radiation. Contrasts greater than 100:1 were achieved. The temporal response as a function of light intensity is presented and the optical switching is shown to be polarization independent.

Azobenzene liquid crystalline materials for efficient optical switching with pulsed and/or continuous wave laser beams.

This study compares optical switching capabilities of liquid crystal (LC) materials based on different classes of azobenzene dyes. LCs based on molecules containing benzene rings with nearly symmetrical pi-pi conjugation respond more efficiently to a cw beam than to a nanosecond laser pulse and maintain the changes induced by the beam for tens of hours. Using azo dye molecules containing two benzene rings with push-pull pi-pi conjugation we demonstrate high photosensitivity to both a cw beam as well as nanosecond laser pulse with only 1 s relaxation of light-induced changes in material properties. Even faster, 1 ms restoration time is obtained for azo dye molecules containing hetaryl (benzothiazole) ring with enhanced push-pull pi-pi conjugation. These materials respond most efficiently to pulsed excitation while discriminating cw radiation.

Study of azo dye surface command photoalignment material for photonics applications.

We provide detailed quantitative characterization of sulfonic bisazodye SD1 as a photoalignment material for photonics applications. The reversibility of photoalignment was tested for transformations between planar and 90 degrees twist orientation states in a liquid crystal (LC) cell using polarized UV light. No degradation was observed for 100 cycles of transformations. A given twist angle of the LC orientation was obtained in a single step, as well as in a sequence of gradually increasing angles. A hysteresis is revealed in the latter case for planar-twist-planar cycles. The material was used for obtaining patterned orientation of a LC polymer providing similarly good quality photoalignment for UV as well as visible light. High efficiency large area and high spatial frequency optical axis gratings (or, polarization gratings) were demonstrated on a polycarbonate substrate. We show the opportunity of obtaining photoalignment in a multilayer system with single exposure to a polarized light. Finally, we provide evidence of a positive feedback in the dynamics of photoalignment due to the orientational effect of an increasing number of aligned molecules.

Fabrication of liquid crystal polymer axial waveplates for UV-IR wavelengths.

We show the opportunity of fabricating axially symmetric waveplates fine tuned to a desired wavelength. High quality waveplates are obtained using liquid crystal polymer layers on photoaligning substrates extending their functional range from UV to IR wavelengths. We characterize the effect of the waveplate on laser beams showing formation of a doughnut beam with over 240 times attenuation of intensity on the axis. We pay attention that the power density is strongly reduced on the doughnut ring as well and use this opportunity for taking charge coupled devices (CCDs) out of a deep saturation regime. Strong deformation of the beam profile is observed when the vortex axis is shifted towards the periferies of the beam. We demonstrate feasibility of using this phenomenon for shaping the profile of light beams with a set of waveplates.

Polarization insensitive imaging through polarization gratings.

Liquid crystal polarization gratings exhibit high diffraction efficiency (approximately 100%) in thin material layers comparable to the radiation wavelength. We demonstrate that they can be combined for polarization-insensitive imaging and optical switching applications. A pair of closely spaced, parallel oriented, cycloidal polarization gratings is capable of canceling the diffractive property of an individual grating. As a result, the phase of the beam is not distorted, and holographic images can be formed through them. An anti-parallel arrangement results in a broader effective diffraction band and doubles the diffraction angle. Broadband diffraction spanning from 480 nm to beyond 900 nm wavelengths has been obtained for a pair of gratings with 500 nm and 633 nm peak diffraction wavelengths. Liquid crystal polymer cycloidal gratings were used in the study showing 98% diffraction efficiency over a large area, and allowed for the use of laser beams expanded to 25 mm. The characteristics of combined cycloidal gratings were tested with laser beams at both UV and red wavelengths.

Optical switching of liquid-crystal polarization gratings with nanosecond pulses.

Optical switching with single nanosecond laser pulses of 532 nm wavelength is reported using high-efficiency optical axis gratings made with a nematic liquid crystal doped with an azobenzene dye. The azobenzene dye we have synthesized exhibits enhanced photosensitivity at green wavelengths, allowing for low threshold switching (approximately 10 mJ/cm(2)). The dye is also characterized by fast relaxation of isomers, allowing for restoration of the diffractive properties of the grating within approximately 100 ms. Change of the diffraction efficiency of the zeroth-order beam from 10% to 70% is observed in a micrometer-thick material layer.

Characterization of optically imprinted polarization gratings.

We provide detailed description and characterization of specifics of the imprinting technique for fabrication of large-area and high-efficiency liquid crystal polymer polarization gratings. We show that the quality of polarization gratings imprinted with linear polarized light is as high as that of gratings obtained in the holographic process, while exhibiting twice larger diffraction angle. The cycloidal polarization pattern used for imprinting is obtained from a master polarization grating, and the importance of fine tuning of its peak diffraction wavelength to the wavelength of imprinting radiation is emphasized. Tuning of the peak diffraction wavelength of imprinted polarization gratings from UV to near IR was realized with the aid of multilayer structures. Since the imprinting process does not involve a holographic setup, it is insensitive to ambient conditions and vibrations and provides an opportunity for large scale production of polarization gratings.

Nonlinear optical transmission of lead phthalocyanine-doped nematic liquid crystal composites for multiscale nonlinear switching from nanosecond to continuous wave.

We have formulated composites of lead (II) tetrakis (4-cumylphenoxy) phthalocyanine (PbTCPc) doped into nematic liquid crystal (LC), 4(')-pentyl-4-biphenylcarbonitrile (5-CB), that has received a 90 degree twisted alignment and investigated the nonlinear transmission properties using both pulsed (Nd:YLF 524 nm, 5 ns) and cw (532 nm) lasers. In the nanosecond regime, this compound is a reverse saturable absorber performing similarly to low-concentration solutions of PbTCPc. Under cw conditions, we observe optically self-activated polarization switching with low threshold input energy. Our results suggest the potential for an all-optical switch working from the nanosecond time scale to cw.

PINK1 attenuates mtDNA release in alveolar epithelial cells and TLR9 mediated profibrotic responses.

We have previously shown that endoplasmic reticulum stress (ER stress) represses the PTEN inducible kinase 1 (PINK1) in lung type II alveolar epithelial cells (AECII) reducing mitophagy and increasing the susceptibility to lung fibrosis. Although increased circulating mitochondrial DNA (mtDNA) has been reported in chronic lung diseases, the contribution of mitophagy in the modulation of mitochondrial DAMP release and activation of profibrotic responses is unknown. In this study, we show that ER stress and PINK1 deficiency in AECII led to mitochondrial stress with significant oxidation and damage of mtDNA and subsequent extracellular release. Extracellular mtDNA was recognized by TLR9 in AECII by an endocytic-dependent pathway. PINK1 deficiency-dependent mtDNA release promoted activation of TLR9 and triggered secretion of the profibrotic factor TGF-ß which was rescued by PINK1 overexpression. Enhanced mtDNA oxidation and damage were found in aging and IPF human lungs and, in concordance, levels of circulating mtDNA were significantly elevated in plasma and bronchoalveolar lavage (BAL) from patients with IPF. Free mtDNA was found elevated in other ILDs with low expression of PINK1 including hypersensitivity pneumonitis and autoimmune interstitial lung diseases. These results support a role for PINK1 mediated mitophagy in the attenuation of mitochondrial damage associated molecular patterns (DAMP) release and control of TGF-ß mediated profibrotic responses.

Observation of nonlinear transmission enhancement in cavities filled with nonlinear organic materials.

We show experimental and theoretical results for enhancement of nonlinear transmission (NT) in moderate finesse cavities filled with nonlinear organic materials (NLOM). Our design for enhancement of nonlinear transmission using micro NLOM cavities compared with reference samples of the same material show that single cavities can enhance the nonlinear response by a factor of 10 or greater under high-absorption conditions. Further enhancement can be achieved in multiple-cavity structures. Other advantages of the cavity structures for nonlinear transmission, such as a higher damage threshold and a broader NT band, are also discussed. Our initial experimental results show a threefold reduction in the nonlinear threshold fluence in a single cavity device compared directly to an identical sample without mirrors, in qualitative agreement with our calculations.

Time-resolved studies of photoinduced birefringence in azobenzene dye-doped polymer films.

We measured transient photoinduced birefringence (delta n) in various azobenzene dye films by pumping with a nanosecond pulse at 532 nm and probing at 633 nm. The switch-on times for the photoinduced birefringence range from nanoseconds to milliseconds and are systematically related with the lowest optical transition energies for those films. Moreover, our results suggest that the transient photoinduced birefringence measurement is a convenient way to determine the relative energies of pi-pi(*) and n-pi(*) states in azo-based materials.