Search

It has been just over 20 years from the first disclosure of a thin and transparent film that would allow controlling propagation of light, an unpolarized and broadband light, with 100% efficiency. First it was an idea seemingly at odds with conventional optics. Then came demonstrations of the thinnest planar optics - “prisms”, lenses, beam shapers, arrays and vortices, switchable or not, - in sizes currently 8” and larger. Novel film architectures extended spectral and angular bandwidths of planar optics to unprecedented scales, changing the ways optics is made and opening avenues to long cherished dreams of adaptation, tunability, multifunctionality, and cost. History is in the making and will be presented first hand with an outline of the marvels in functionality and capabilities waiting for optics behind the horizon.

A new generation of reconfigurable optical components is conceived by bridging the photothermal properties of gold nanoparticles and the thermosensitivity of liquid crystalline materials. As such, gold nanorods (GNRs) heated using light are used to activate efficient hidden diffraction gratings realized in a blend made of a room temperature polymerizable liquid crystal (PLC) and nematic liquid crystal (NLC). Holographic liquid crystal polymer dispersed liquid crystal (HLCPDLC) gratings containing a small percentage of GNRs are fabricated with periodicity of 2.6 ?m by means of a conventional UV holographic recording setup. The HLCPDLC structures are characterized using morphological, optical, and thermooptical techniques. Because of the initial refractive index match between the polymer-rich and LC-rich regions, the "grating" is hidden and the films appear transparent and nondiffractive. Illumination of these GNR-containing structures with a suitable light source (808 nm) induces a local heating due to the plasmonic absorption of the GNRs. This heating induces a refractive index mismatch between the PLC and the NLC as the latter undergoes a phase transition from nematic to isotropic, finally resulting in a transmission diffractive structure activated over a few seconds exhibiting an efficiency of about 70%. The same HLCPDLC samples have also been tested as thermosensitive waveplates, enabling a new, fast methodology for quantifying the photoinduced plasmonic heating with a thermal sensitivity of ?0.04 °C. Moreover, thermoplasmonic driven waveplates represent a new avenue in the field of light controllable optical phase modulators.

The contrast of astronomical coronagraphs based on vector vortex waveplates (VWs) depends critically on precision of fulfilment of half-wave retardation condition for the desired wavelength range. The structure of VWs designed for operation in broad spectral bands is typically rather complex comprising three-dimensional modulation patterns that in practice are obtained in layer-by-layer deposition of liquid crystal polymers (LCPs). Physical properties of each of those layers - thickness, retardation, and orientation modulation pattern, along with layer integrity and quality - need to be maintained with very high precision to ensure contrast requirements of coronagraphs. This inevitably reduces the yield and affects the quality of high contrast VWs. We discuss opportunities of tuning the retardation values of VWs using electric field for liquid crystal (LC) based VWs as well as temperature and optical radiation for LCPs. LC VWs allow also tuning the spectral range of operation and switching the topological charge of the effective VW system.

Thermoplasmonics deals with the generation and manipulation of nanoscale heating associated with noble metallic nanoparticles. To this end, gold nanoparticles (AuNPs) are unique nanomaterials with the intrinsic capability to generate a nanoscale confined light‐triggered thermal effect. This phenomenon is produced under the excitation of a suitable light of a wavelength that matches the localized surface plasmonic resonance frequency of AuNPs. Liquid crystals (LCs) and hydrogels are temperature‐sensitive materials that can detect the host AuNPs and their photo‐induced temperature variations. In this perspective, new insight into thermoplasmonics, by describing a series of methodologies for monitoring, detecting, and exploiting the photothermal properties of AuNPs, is offered. From conventional infrared thermography to highly sophisticated temperature‐sensitive materials such as LCs and hydrogels, a new scenario in thermoplasmonic‐based, next generation, photonic components is presented and discussed. Moreover, a new road in thermoplasmonic‐driven biomedical applications, by describing compelling and innovative health technologies such as on‐demand drug‐release and smart face masks with smart nano‐assisted destruction of pathogens, is proposed. The latter represents a new weapon in the fight against COVID‐19.

Circular dichroism (CD) is an important parameter, characterizing optically active medium. The devices for CD measurements presented on today market measures CD in wide spectral range. The high-precision standard optics, electronics and optomechanics are used in these devices, and data processing requires the application of a complex mathematical apparatus. These devices are quite expensive, have large dimensions, require specially trained staff, and measurement duration is tens of minutes. In this work we present a device for CD measurement on only one wavelength, the key element of which is polarization diffractive waveplate, the optical element of new generation. Device has a number of advantages: easy to use, compact, working in real time, and low cost. These advantages make it ideal for educational programs.

Vector vortex waveplates offer distinct advantages compared to conventional light blocking components for coronagraphs due to their continuous structure, thinness, and transparency. They allow high contrast over a broad band in any spectral region for which the available anisotropic optical materials are transparent. We present opportunities of reducing in-band leakage of vector vortex waveplates to

Diffractive waveplates (DWs) are highly efficient optical components realized by means of a polarization holography setup that makes use of UV/blue laser sources. It is more convenient to perform the holographic recording process with green lasers (e.g., continuous wave operating at 532 nm) because they offer compactness, efficiency, and high power. Unfortunately, the photo-alignment materials used for DW fabrication exhibit limited sensitivity at 532 nm. Herein, we report the realization of cycloidal diffractive waveplates (CDWs) by employing a polarization holographic setup using a high-power, diode-pumped solid-state laser operating at 532 nm. The enabling factor is the use of a photo-alignment material with a broad absorption band extending into the visible part of the spectrum. Samples are characterized in terms of morphological and optical properties. They exhibit a well-defined morphology along with very high diffraction efficiency (≈97%). The possibility to realize CDWs with larger apertures is underway, enabling the realization of a new generation of optical components for integration in modern applications.

Improvements are possible in the tradeoff between bandwidth and diffraction efficiency as well as manufacturability in diffractive waveplate optics. We report recent progress in development and fabrication of diffractive waveplate optics using multi-layer designs, with weighting of the optimization corresponding to the spectral response of the human eye.

Diffractive waveplates (DWs) generally diffract light in different directions for the two circular polarizations of light, and the diffraction efficiency of such devices generally falls when the angle through which light is diffracted becomes large. It would be desirable to be able to make fast (low f-number), high-efficiency lenses with DW type structures. We study the dependence of the efficiency of DWs and polarization volume gratings (PVGs) on the polarization and angle of incidence of light, and identify structures with polarization independent function — the diffraction efficiency and angle of diffraction. The results are obtained for DWs and PVGs periodic in one linear coordinate, however, they are applicable to other optical devices, including lenses based on these structures.

Devices based on diffractive waveplates exhibit diffraction characteristics that are dependent on the polarization and wavelength of light. In applications, switchability, polarization independence, and wavelength independence are often desirable. Here we report on recent developments of diffractive optical elements that have various combinations of switchability, polarization independence, and broad wavelength coverage.

Diffractive waveplates enable stackable ultrathin light-weight large area optics fast-switchable with low-voltage/low power fields. State-of-the-art systems and low-cost manufacturing opportunities will be presented aimed at next generation augmented, virtual reality, flexible, polarizer-free displays, LiDARs, etc.

Controlling light propagation at the nanoscale is a fascinating opportunity offered by modern photonics, more than a challenge to face off. This study is aimed at investigating a particular kind of nanocomposite and reconfigurable optical metamaterials that can be exploited for the realization of a new class of switchable photonic devices, representing a breakthrough with respect to the state of the art. Existing photonic devices exhibit, in general, a drawback in the absence of tunability; this work aims to the design and characterization of metamaterials exploiting reconfigurable media, like LCs, which enable realization of a tunable, high quality, photonic quasi-crystal based switchable mode selector. It turned out that, starting from an unpolarized white light source, through a light extraction mechanism based on the diffraction of light, the high quality structure, combined with a uniformly aligned Photo-responsive Liquid Crystal (PLC), is able to give rise to an extremely narrow (FWHM ≈5 nm) and linearly polarized single mode peak of the extracted light intensity. Moreover, we have shown that the spectral properties (switching) of the samples can be finely controlled by using both an external applied voltage and a suitable pump light source with a maximum increase of 45% of the extracted light. Finally, both Scanning Electron Microscopy (SEM) and Far Field Diffraction (FFD) analysis have shown the high quality morphology of the realized structure.

Technique for real-time spectropolarimetry is developed. An embedded system for circular dichroism registration is designed based on National Instruments single board reconfigurable I/O platform for ultraviolet and visible spectroscopic needs. The basic functional unit of the proposed device is liquid crystal polarization diffraction grating. In order to expand the dynamic range the control of data accumulation time is provided. Two NMOS sensor linear arrays provide an excellent linearity of response.

The optical power of diffractive waveplate structures is limited not as much by fabrication technology issues as by the fundamental features of light propagation in complex anisotropic structures. The infinitely thin two-dimensional film approximation does not apply, and the efficiency of 4G lenses, prisms, etc., is reduced for geometries corresponding to sharp focusing lenses and large diffraction angles. Due to thin-film nature, these films can be combined to reduce effective focal length, increase effective diffraction angle, topological charge, etc. Along with this, we will discuss the opportunity of increasing optical power of 4G lenses, prisms, etc. without compromising efficiency.

We report about developing long-wave infrared diffractive optical components based on liquid crystals. The components show high efficiency and high transparency for the 10.6 μm wavelength of CO2 laser beam.

Near 100% broadband efficiency of polarization holograms provides opportunities for shaping light beams, imaging, and displays. Thin, flexible and switchable between different optical states and functions, novel optical components and systems are smarter than ever.

This feature issue of the journal is the first one to bring together ongoing research from many groups developing diffractive waveplate technology. This technology combines the best of three worlds—the thinness of diffraction gratings, the broad bandwidth and high efficiency of conventional refractive optics, and the low-cost fast manufacturing of polymer optics even in large area. The technology is at the intersection of polarization holography and polarization gratings, Pancharatnam–Berry or geometrical phase optics, waveplates, metasurfaces and planar optics. Optics will never be the same again!

A narrow - linewidth, hot isostatic treated Cr:ZnSe laser was non - mechanically tuned over a total wavelength range of 195 nm by a novel organic liquid crystal etalon. The narrow - linewidth laser was continuously tuned by applying a 1 kHz square wave signal of 1 – 5 Vpp to the intracavity 9 THz nominal free spectral range liquid crystal etalon. The maximum and minimum lasing wavelengths were 2650 nm and 2455 nm, respectively, and a maximum average output power of 475 mW was recorded at 2503 nm. This work demonstrated continuous tuning, while maintaining an intrinsic narrow-linewidth ≤ 900 MHz. The results presented in this work are attributed to the low insertion loss of the liquid crystal etalon at ≤ 5%. It is believed that this is the first demonstration of purely electronic tuning of a mid-IR laser by an organic liquid crystal etalon.

A general geometric phase singularity array structure is presented and discussed. For any two-dimensional point lattice, a singularity array is defined as a summation of helical phase singularities with alternating handedness. The phase angle is the slow-axis orientation of a varying half-waveplate. Arrays are demonstrated in photoaligned polymer liquid crystal films. Simple square and biomimetic spiral lattices are characterized for diffraction behavior. Pattern selection rules based on topological charge are discovered. Numerical decomposition shows that diffracted beams are composites of a few ordered planewaves for square phase arrays and Bessel beams for spiral phase arrays. Orbital angular momentum spectra of spiral diffraction are directly measured.

We present a collinear, common-path image-inversion interferometer using the polarization channels of a single optical beam. Each of the channels is an imaging system of unit magnification, one positive and the other negative (inverted). Image formation is realized by means of a set of anisotropic lenses, each offering refractive power in one polarization and none in the other. The operation of the interferometer as a spatial-parity analyzer is demonstrated experimentally by separating even- and odd-order orbital angular momentum modes of an optical beam. The common-path configuration overcomes the stability issues present in conventional two-path interferometers.

Soft composite materials combined with a holographic photopolymerization process are used for realizing an innovative switchable periodic structure made of slices of almost pure polymer alternated with films of well aligned nematic liquid crystals named POLICRYPS. It exhibits negligible scattering losses, while the effect of the spatial modulation of the refractive index (from polymer to nematic liquid crystal) can be switched on and off by applying a low (few V/μm) electric field. The diffractive properties of the POLICRYPS structure are characterized in terms of cell thickness, impinging probe angle and wavelength revealing a strong correlation between the diffraction efficiency and all the above mentioned parameters. These results are very attractive for many applications such as switchable Bragg gratings for telecom devices, phase modulators, and displays. Other advantages of the technology include absence of an alignment layer, absence of haze, robust structure, and inexpensive manufacturing. In addition, no special alignment layers are required. This is a unique opportunity and a big advantage compared to conventional liquid crystal devices. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 158–162

Circularly polarized light is employed to write information into cholesteric liquid crystal (CLC) cells that initially exhibit homogeneous planar alignment and are fabricated with a photoaligning boundary layer. Overlap of the writing beam with light reflected from the CLC phase disrupts the reflective Grandjean texture, resulting in a localized region that strongly scatters light. These scattering areas can be geometrically patterned using circularly polarized light and a mask, erased and brought back to the original reflective condition by exposure to linearly polarized light, and then repatterned with a different mask using circularly polarized light. The light-induced scattering is localized to the side of the cell being exposed. Within the scattering region a microscopic texture is formed, which exhibits an average feature, or “domain”, size related to cell thickness and helical pitch. The behavior occurs only when the CLC and incoming writing radiation exhibit the same handedness and when the reflection bandwidth of the CLC is commensurate with the wavelength of the incoming radiation. This new phenomena provides the ability to reconfigure reflectivity from a CLC cell and is expected to be useful for systems where all optical control of dynamic information is needed.

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.

The fourth generation optics (4G optics) enables the realization of novel optical components (lenses, gratings, vector vortices, etc.) by patterning the optical axis orientation in the plane of an anisotropic film. Such components exhibit near 100% diffraction efficiency for wavelengths meeting half-wave retardation condition. In this framework, we have advanced a step-forward by realizing different diffractive waveplates (DWs) with arbitrary spatial patterns of the optical axis orientation by exploiting the capability 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 is that the orientation of the alignment layer, and therefore of the fabricated liquid crystal (LC) or liquid crystal polymer (LCP) DWs, can be specified on a pixel-by-pixel basis. By varying the optical magnification or de-magnification between the SLM and the alignment layer, the spatial resolution of the photoaligned layer can be adjusted to be optimal for each application. We show that with a simple “click” it is possible to record different high resolution optical components as well as arbitrary patterns ranging from lenses to invisible and even dual labels.

The thickness of functional layers in liquid crystal photonics devices is negligibly small compared to the substrates. New opportunities provided by multilayer 4G optical systems require minimizing the thickness of each layer. We report about our progress made by developing technology of thin flexible substrates, functional polymer films, solid electro-optical layers, and graphene oxide based electro-conductive coatings.

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.

The fourth generation of optics uses modulation of optical axis orientation in anisotropic materials for achieving a wide variety of optical functions. 4G optical components blend the thinness of zero-order waveplates with the high efficiency one gets with Bragg volume holographic gratings and in a broad band of wavelengths typical of conventional glass lenses, prisms, etc. (the first generation of optics). We will discuss the technology for applications in communications and astronomy. Particularly, we will present challenges and opportunities for fabrication of vector vortex waveplates and cross-waveplates for coronagraphy, and waveplate lenses — Pancharatnam-Berry phase lenses — for optical communications and imaging.

We report on the thermo-optical properties of gold nanorods (GNRs) dispersed in a thermotropic cholesteric liquid crystal (CLC). We have characterized the CLC reflection band behavior for two different cell thicknesses under the influence of a suitable (resonant) pump beam. It turns out that for the 1.6 mu m thick cell there is a suppression of the CLC reflection band for both pure CLC and CLC/GNRs. For the 10 mu m thick cell, the presence of GNRs desensitizes the shift of the CLC reflection band to temperature. Suitable cell design enables one to 'turn off' the wavelength shift of the peak reflection, thereby turning the system into a pure amplitude measurement tool. This has implications where the probe wavelength is fixed at a common, single wavelength.

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.

Modulating orientation of optical anisotropy axis can transform half-wave retardation films into lenses, prisms, axicons, spiral phase plates, and more. Polarization holography, particularly, digital, expands the variety and capabilities of the new generation optics. Article not available.

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.

Photosensitive liquid crystals (PLCs) are promising materials that can combine a high-refractive-index modulation, typical of LCs, with high photosensitivity, due to the presence of photochromic molecules such as azobenzene and derivates. [1] These can undergo a reversible isomerization from a thermodynamically stable trans to a cis conformation when acted on by UV or visible light; a reverse transition can be obtained upon heating or irradiation with a different (longer wavelength) visible light. Thanks to these materials andprocesses, thepossibility toconfine and stabilize photosensitive materials has been considered in the past [2] and the perspective of producing fast photonic devices of scientific and technological interest looks highly realistic. There is, however, a serious problem represented by instability far from room temperature. [2] One way to reduce this effect has been found in using composite polymeric materials: [3] Holographic diffraction gratings, which exploit LC composite materials (HPDLCs), [4] are low-cost components with a wide range of possible photonic and optoelectronics applications. Therefore, the possibility of fabricating an optically controllable photonic device has been investigated by combining the photosensitivity of azobenzene materials with the optical properties of HPDLCs. [5] Devices of this kind can exhibit, however, an intrinsic drawback when the droplet size of the LC component inside the polymeric matrix is comparable with the wavelength of the diffracted light, thus yielding a strong light scattering. [6] Recently, a good improvement has been obtained by using a new kind of holographic diffraction grating with better optical qualities, which consists of polymer slices alternated to films of regularly aligned nematic LC (NLC). Depending on the particular procedure utilized for its fabrication, this structure is called POLIPHEM [7] orPOLICRYPS [8] andisobtainedby UV-curingofa mixture of monomer and NLC. In a recent attempt [9] to fabricate

We report on the laser and sunlight driven, fast and large oscillation of cantilevers composed of photoresponsive liquid crystal polymer materials. The oscillation frequency, driven with a focused 100 mW laser of multiple wavelengths (457, 488, 514 nm), is as high as 270 Hz and is shown to be strongly correlated to the physical dimensions of the cantilever. The experimental frequency response is accurately described by the calculated natural resonant frequency for a non-damped cantilever. To further understand the conversion efficiency of light energy to mechanical work in the system, the oscillatory behavior of a 2.7 mm × 0.7 mm × 0.04 mm cantilever was examined at pressures ranging from 1 atm to 0.03 atm. A large increase in amplitude from 110° at STP to 250° at low pressure was observed. A first approximation of the system efficiency was calculated at 0.1%. The large increase in amplitude at low pressure indicates strong hydrodynamic loss and thus, the material efficiency is potentially much greater. Using a simple optical setup, oscillatory behavior was also demonstrated using sunlight. This work indicates the potential for remotely triggered photoactuation of photoresponsive polymer cantilevers from long distances with lasers or focused sunlight.

Phototuning of more than 2000 nm is demonstrated in an azobenzene-based cholesteric liquid crystal (azo-CLC) consisting of a high-helical-twisting-power, axially chiral bis(azo) molecule (QL76). Phototuning range and rate are compared as a function of chiral dopant concentration, light intensity, and thickness. CLCs composed of QL76 maintain the CLC phase regardless of intensity or duration of exposure. The time necessary for the complete restoration of the original spectral properties (position, bandwidth, baseline transmission, and reflectivity) of QL76-based CLC is dramatically reduced from days to a few minutes by polymer stabilization of the CLC helix.

The ability of optical axis gratings (OAGs) to fully transfer the energy of an unpolarized incident light beam into the ±1st diffraction orders is explored below for development of a polarization-independent optical system with nonlinear transmission. Diffractive properties of OAGs based on azo dye doped liquid crystals (azo LCs) are efficiently controlled with low power radiation. Switching from diffractive to transmissive states of the OAG takes place within 50 ms at 60 W/cm2power density level, while the diffractive state is restored within ~ 1 s in the absence of radiation. High contrast optical switching is demonstrated with violet as well as green laser beams. A photoswitchable OAG is paired with a light-insensitive OAG in diffraction compensation configuration to obtain an optical system switchable from high to low transmission state. The thinness of OAGs required for high contrast switching ensures high overall transmission of the system. Given also the spectrally and angularly broadband nature of OAG diffraction and the capability of azo LC material systems to respond both to cw as well as short laser pulses makes the optical system under discussion very promising for optical switching applications. Presentation of these results is preceded by an "opinionated" review of prior developments and demystifying of the fabrication technique of high efficiency large area OAGs.

We report on the fast and optically controlled angular bending of cantilevers made from liquid crystal polymer networks functionalized with azobenzene moieties (azo-LCN). For potential applications such as adaptive optics, photoresponsive cantilevers should rapidly deform to controlled angles while maintaining a modulus that can accomplish appreciable mechanical work. This work demonstrates cantilevers made of monodomain azo-LCN containing pendant (side chain) azobenzene mesogens with a storage modulus of 1.4 GPa bend 85° in less than 300 ms upon exposure to 442 nm irradiation. Moreover, the bending angle of these monodomain azo-LCN cantilevers can be controlled by the polarization angle of the source relative to the long-axis of the cantilever. The bending performance (deformation angle and speed) of this monodomain system is compared to a polydomain analogue. The impact of azobenzene concentration, laser intensity, and thickness on these parameters is also presented.

Phototuning of Bragg reflection bandgap from green to blue and from red to green wavelengths was induced with a green (λ = 532 nm) laser beam in a cholesteric liquid crystal based on highly sensitive azobenzene nematic BEAM 1005 (BEAM Co.) and UV transparent non-photoisomerizable optically active dopant ZLI-6248 (R-2011) (Merck Ltd.). Optical switching between reflected and transmitted beams, as well as nonlinear transmission and reflection due to Bragg reflection band shift are studied in detail.

Cholesteric liquid crystals (CLCs) which possess a periodicity in the visible portion of the spectra, exhibit selective reflection of circularly polarized light. The ability to modulate this color through a variety of means has been explored, including work which incorporated azobenzene LCs. Two types of systems have recently been explored utilizing wavelength-specific cis-trans isomerization processes, which enable unprecedented photosensitivity. The first system exhibits large blue or red-shifted changes in reflection wavelength upon visible irradiation. The second system exploits the metastable, long-lived photoinduced isotropic state, whose return to the reflective Grandjean texture can be induced by wavelength-specific radiation. We demonstrate nonlinear transmission from both types of systems, starting with submicrowatt power levels and spanning over four orders of magnitude dynamic range. The power dependence and temporal evolution of this effect (10–100 ms) is documented here for red or green laser wavelengths. The effect for the former case is due to bandgap auto-tuning, when the laser beam is tuning the CLC Bragg reflection band to its own wavelength. For the latter case, autonomous, optical feedback due to bandgap restoration is the cause of the nonlinear transmission properties.

We study the process of orienting nanoparticle dispersed liquid crystals (NPD‐LCs) with the aid of low‐frequency (1–100 Hz) shearing microvibrations (1–10 µm amplitude). Due to the random orientation of LCs in such networks, NPD‐LCs are highly light scattering unless subject to the orienting influence of a high‐voltage electric field (∼100 V). We show that microvibrations are able considerably to enhance the stable NPD‐LC transmission state obtained due to the application of an electric field. Shearing microvibrations make it feasible to switch between the transparent and opaque states of the material in an all‐mechanical process. The optical transmission of the material proves to be very sensitive to the vibration amplitude as well as frequency. As a result, the system can be used for sensing and measuring low‐frequency and small‐amplitude mechanical oscillations.

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.

We present new lenses – waveplate lenses created in liquid crystal materials. Waveplate lenses allowed focusing and defocusing laser beam depending on the sign of the circularity of laser beam polarization. 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. Lenses of varied size and focal length are presented.

We examine the idea to use self-focusing in a non-linear liquid crystal to increase the accuracy of measurements of wavefront distortions with an active Shack–Hartmann sensor. This modification should improve the measurement accuracy by two orders of magnitude.

We present a simple method to convert a Gaussian laser beam into an annular beam using a homeotropically oriented nematic liquid crystal. The method allows creation of a beam with sub-millimeter diameter and a width of a few tens of microns for a propagation distance of more than 10 mm. High spatial gradients in the radial intensity distribution make the beams promising for use in atom trapping and guiding.

We report on distinct dynamic regimes of optically induced redistribution of molecules in a reacting material. The physical system is a mixture of photopolymerizable monomer and nematic liquid crystal with space-time modulated diffusivity. An empirical model is developed which provides an excellent description of all the stages of the experimentally observed highly intricate dynamics. This dynamics is governed by spatially inhomogeneous photogeneration of radicals, their diffusion, and the photopolymerization-induced change in the diffusion constant.

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.

A novel chirped polymer/liquid crystal diffraction grating (POLICRYPS) structure with periods ranging from 10 µm to 100 µm is reported. The chirped gratings are realized by using a single beam curing process through a diffractive waveplate mask with varying periodicity. The quality of the nematic liquid crystal (NLC) alignment inside the chirped structures as a function of periodicity was investigated using a polarized optical microscope technique. The extent of phase separation between the polymer and the NLC improves as the average spacing between the polymeric walls gets smaller. In the regions where phase separation is most complete, the duty cycle of the grating is proportional to the initial concentration of the two main components (polymer and NLC). The degree of order of the NLC within the phase separated channels was measured with a Mueller Matrix Spectroscopic Polarimeter. There is strong experimental evidence that the orientation of the NLC molecular director inside the structure is perpendicular to the surface of the polymer phase separated walls. Electro-optic measurements reveal a strong correlation between the on–off response times and the average distance between the polymeric walls. Our findings opens new avenues to realize a new generation of LCs based devices without using surface treatment or functionalization.

Diffractive waveplate technology presents an opportunity for designing arrays of all types of optical components. We present here different architectures of arrays of waveplate lenses and vector vortex waveplates. Due to the continuous nature of diffractive waveplate coatings and the high spatial resolution of the technology, the sizes of array elements can span from micrometers to tens of millimeters. Both fixed and electrically switchable arrays are discussed. Arrays of diffractive waveplates present new challenges and opportunities for digital light polarization holography for applications in polarizer-free displays, smart windows, optical communications, beam shaping, and other photonics technologies.