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This study presents an innovative application of inkjet printing technology in the construction of a switchable optical vortex beam generator. The fabrication process involves drop‐on‐demand printing of liquid crystal (LC) droplets that can generate an optical vortex beam in the far‐field with the application of a voltage. Notably, this vortex beam can be activated and deactivated by manipulating the amplitude of the electric field. Both simulations and experiments are used to determine the optical characteristics of the printed LC devices and the resulting far‐field patterns for different polarizations of light. The study showcases the versatility of the generator in that it can produce both vortex and vector beams, the choice of which is simply determined by the polarization of the input light. This highlight the potential of this printed LC technology for integration into a multitude of optical systems. [ABSTRACT FROM AUTHOR]

A polarization controllable band‐edge liquid crystal (LC) laser configuration is presented that provides on‐demand control of the polarization state of the laser using a four electrode in‐plane configuration to drive a nematic LC layer. By controlling the orientation of the electric field, and thus the orientation of the optic axis of the nematic LC, as well as the retardance, any laser polarization state (e.g., circular, elliptical) can, in principle, be created that is aligned along any desired direction in a plane perpendicular to the propagation direction. After calibrating the tuneable nematic device with a He‐Ne laser that has a well‐defined polarization state, control of the LC laser polarization is then demonstrated, where it is shown that different polarization states and orientations thereof can be obtained by changing the relative combination and amplitudes of the voltages applied to each of the four electrodes. It is found, however, that achieving a pure linear polarization state is challenging, which may indicate that the polarization from the LC laser is not a well‐defined circularly polarized state. These thin‐film LC lasers with full polarization control are potentially important for a variety of different applications ranging from the biomedical to the display industries. [ABSTRACT FROM AUTHOR]

In this paper, drop‐on‐demand (DoD) printing is demonstrated of polymer stabilized chiral nematic liquid crystal (PSCLC) privacy windows that can function in either a conventional mode (scattering to transparent) or reverse mode (transparent to scattering) with the application of an electric field. Inkjet printed droplets of the PSCLC mixture, with diameters of the order of 100–200 µm and sandwiched in LC layer thicknesses of ≈10–15 µm, are characterized in terms of their transmission as a function of the electric field amplitude and the response times for switching into and out of the scattering state. The results show that the printed droplets, and arrays thereof, exhibit similar electro‐optical properties to analogous thin‐film devices, but with the ability to incorporate bespoke features such as images and decorative patterns. Finally, the electro‐optical switching of a printed PSCLC privacy window whereby alphanumeric characters can be made to appear and disappear with the application of an electric field is demonstrated. [ABSTRACT FROM AUTHOR]

Conventional polymer dispersed liquid crystal (PDLC) films have been successful as electrically‐switchable screens for privacy applications. However, spatial patterning of the films so as to generate a visually appealing design, logo, or image typically requires intricate fabrication processes, such as the use of prefabricated photomasks that do not allow for on‐demand designs. Herein is reported on the fabrication and characterization of spatially patterned PDLC "pixels" using drop‐on‐demand inkjet printing, and it is demonstrated how these materials can be used to form a new generation of smart windows that consist of embedded images or company logos, which can be made to disappear with the application of a voltage. Following refinements to the material rheology and the subsequent successful deposition of individual PDLC droplets, arrays of PDLC pixels are printed at a resolution of 250 pixels per inch with an individual pixel size of 130 µm operating at an electric field strength (E) of E = 1.4 V μm−1. Finally, using the approach developed herein, these printed PDLC pixels are arranged to form a college emblem that is embedded within a smart window that can be made to disappear with the application of a voltage. [ABSTRACT FROM AUTHOR]

The artefact known as speckle can plague numerous imaging applications where the narrow linewidth of laser light is required, which includes laser projection and medical imaging. Here, we report on the use of thin-film chiral nematic liquid crystal (LC) devices that can be used to mitigate the influence of speckle when subjected to an applied electric field. Results are presented which show that the speckle contrast (a quantitative measure of the presence of speckle) can be significantly reduced by decreasing the pitch of the chiral nematic LC from 2700 to 244 nm. Further reduction in the speckle contrast can be observed by operating the diffuser technology at a temperature close to the chiral nematic to isotropic transition. At such temperatures, we observe a simultaneous improvement in the transmission of light through the device and a decrease in the electric field amplitude required for the minimum speckle contrast value. We conclude by presenting a laser projected image of the 1951 USAF target with and without the LC device to demonstrate the visual improvement as a result of the speckle reduction. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate analog phase modulation in a transmissive configuration using the flexoelectro-optic effect in short-pitch chiral nematic liquid crystal (LC) devices. Two different modes are considered, both of which are shown to generate full 2π phase modulation at 1 kHz switching frequency. The first configuration that is considered consists of a half-wave plate that is placed between two flexoelectro-optic LC devices that are subjected to electric fields that are applied in phase. Second, we demonstrate that a similar phase modulation response can be observed by removing the half-wave plate and subjecting the two flexoelectro-optic LC devices to electric fields whereby the polarities are out of phase. Both configurations demonstrated herein are promising for the development of next-generation LC spatial light modulators, particularly when reflective geometries are challenging or impractical. [ABSTRACT FROM AUTHOR]

Smectic A liquid crystals, based upon molecular structures that consist of combined siloxane and mesogenic moieties, exhibit strong multiple scattering of light with and without the presence of an electric field. This paper demonstrates that when one adds a laser dye to these compounds it is possible to observe random laser emission under optical excitation, and that the output can be varied depending upon the scattering state that is induced by the electric field. Results are presented to show that the excitation threshold of a dynamic scattering state, consisting of chaotic motion due to electro-hydrodynamic instabilities, exhibits lower lasing excitation thresholds than the scattering states that exist in the absence of an applied electric field. However, the lowest threshold is observed for a dynamic scattering state that does not have the largest scattering strength but which occurs when there is optimization of the combined light absorption and scattering properties. [ABSTRACT FROM AUTHOR]

Covering a nano-patterned titanium dioxide photonic crystal (PC) within a well-oriented film of dye-doped liquid crystal (LC), a distributed feedback laser is constructed whereby the emission characteristics can be manipulated in-situ using an electric field. This hybrid organic-inorganic structure permits simultaneous selectivity of both the beam pattern and laser wavelength by electrical addressing of the LC director. In addition, laser emission is obtained both in the plane and normal to the PC. Along with experimental data, a theoretical model is presented that is based upon an approximate calculation of the band structure of this birefringent, tuneable laser device. [ABSTRACT FROM AUTHOR]

Using in-plane electric fields, the electrical induction of the uniform lying helix (ULH) alignment in chiral nematic liquid crystals is reported. This process permits spontaneous induction of the ULH alignment to give an in-plane optic axis, without the need for complex processing. Flexoelectro-optic switching is subsequently obtained by holding the in-plane electrodes at a common voltage and addressing via a third, plane-parallel electrode on a second, or upper, substrate to give a field across the device in the viewing direction. For this device, in optimized bimesogenic materials, we demonstrate full intensity modulation and sub-millisecond response times at typical device temperatures. [ABSTRACT FROM AUTHOR]

Using a chiral nematic liquid crystal with a negative dielectric anisotropy, it is possible to switch between band-edge laser emission and random laser emission with an electric field. At low frequencies (<1 kHz), random laser emission is observed as a result of scattering due to electro-hydrodynamic instabilities. However, band-edge laser emission is found to occur at higher frequencies (>5 kHz), where the helix is stabilized due to dielectric coupling. These results demonstrate a method by which the linewidth of the laser source can be readily controlled externally (from 4 nm to 0.5 nm) using electric fields. [ABSTRACT FROM AUTHOR]

In this letter, the authors demonstrate photonic band gap (PBG) tuning in chiral nematic liquid crystals using electrically commanded surfaces consisting of a ferroelectric liquid crystal. The electrically commanded surfaces generate a contraction of the pitch of the chiral nematic which is manifested as a blueshift of the PBG. Results are presented which demonstrate that tuning can be achieved by either varying the frequency or the amplitude of the electric field. The maximum shift observed for the long-wavelength band edge was 23 nm for an electric field strength of 20 V μm-1 and a frequency of 800 Hz to 1 kHz. [ABSTRACT FROM AUTHOR]

In this letter, the authors demonstrate reversible color switching from blue to red in polymer stabilized chiral nematic liquid crystals when viewed at oblique angles. A series of unusual colored scattering states, different from those noted in polymer-free samples, was observed in cells that had been prepared using a technique of cooling the sample from the isotropic phase in the presence of a low frequency (80 Hz) applied electric field and then photopolymerizing the sample on both sides of the cell. This process “freezes-in” a texture whereby the helix axis lies preferentially in the plane of the cell. [ABSTRACT FROM AUTHOR]

• The paper reports the development of a new liquid crystal (LC) optical phase modulator that can lead to full 2 π phase modulation combined with response times that are on the order of 1 ms. • Full 2 π phase modulation can be achieved at driving voltages that are readily accessible using existing silicon backplane technology. • The phase modulator is based on the fast-switching behaviour when operated in the symmetric H state of a nematic pi-cell. • Results are presented demonstrating the electric field conditions required to prolong the stability of the symmetric H state. • The experimental results are found to be in good agreement with results from simulations based upon Ericksen-Leslie continuum theory. In this paper, we investigate the optical phase modulation potential of a nematic liquid crystal (LC) pi-cell operating in the so-called symmetric H (Hs) state. Experimental results of the optical phase modulation obtained using a phase-shifting Michelson interferometer are presented which are then compared with results from simulations carried out using Ericksen-Leslie continuum theory. The stability of the Hs state, which is limited, is investigated by adjusting the amplitude of the applied voltage and the duration of the voltage burst. To achieve full 2π phase modulation with 1 ms timescale in a reflective geometry (akin to that of a spatial light modulator), we employ a short burst voltage to drive the LC pi-cell into the Hs state, which shows excellent phase modulation capability, and the experimental results are found to be in good agreement with the results from simulations. [ABSTRACT FROM AUTHOR]