[en] We demonstrate a liquid crystal (LC) droplet whose surface profile could be deformed by a fringing field. In the voltage-off state, the LC droplet exhibits a pillared shape by touching both substrates. As the voltage increases, such a droplet could be stretched to a cone-like shape or thin film. For a 1.5 mm aperture LC droplet, its occupied area could be expanded by ∼4.3x at 6.5 V_rms μm^-1. Upon removing the voltage, the droplet could fully recover to its original shape. The shape stretching and recovering time are dependent on the expanded area. With the support of silicon oil around the droplet, the device is stable and the gravity effect is negligible.

[en] All-fiber curvature sensors based on a liquid crystal-filled fiber Mach–Zehnder interferometer (LCF-MZI) are proposed and experimentally demonstrated for high performance measurements of very small curvatures from 0 to 0.0667 m⁻¹, which is usually hard to be precisely monitored by well-known methods. Such a curvature sensor can be easily fabricated by splicing a section of an LC-filled hollow core fiber between two single mode fibers. Our experimental results show that the maximum curvature sensitivity of the proposed sensor is  −724.3 nm/m⁻¹ for a wavelength shift and 632 dB/m⁻¹ for peak intensity. These results are at least 10 times better than those of previously reported fiber interferometer sensors. (paper)

[en] We demonstrate a high sensitivity all-fiber Mach–Zehnder interferometer (MZI) based on radial-aligned liquid crystal (LC) in a hollow optical fiber (HOF). The transmission spectrum of the liquid crystal-filled fiber MZI (LCF-MZI) was measured at different temperatures, and the thermal-induced wavelength shift of the interference spectrum probed. The experimental results indicate that the LC alignment and refractive indices inside the hollow capillary are significantly influenced by the temperature, which in turn changes the optical properties of LCF-MZI. Our experimental data on notch wavelength shift agree well with the measured refractive index temperature gradient. (paper)

[en] We report a high density liquid crystal (LC) droplet array for non-contact inspection. The incident light is modulated by changing the shape of each droplet using a dielectric force even though the electrode and droplet array are separated by a fairly large air gap. The reshaped LC droplets cause colour change which is easily inspected by the human eye. In a sample with 30 μm thick polymer cavity and 130 μm air gap, LC droplet surface reshaping is clearly observed as the applied voltage exceeds 40 V_rms. Potential application of such a LC droplet array for inspecting the defected thin-film-transistor pixels is emphasized.

[en] A high ambient contrast ratio display device using a transparent organic light emitting diode (OLED) or transparent quantum-dot light-emitting diode (QLED) with embedded multilayered structure and absorber is proposed and its performance is simulated. With the help of multilayered structure, the device structure allows almost all ambient light to get through the display device and be absorbed by the absorber. Because the reflected ambient light is greatly reduced, the ambient contrast ratio of the display system is improved significantly. Meanwhile, the multilayered structure helps to lower the effective refractive index, which in turn improves the out-coupling efficiency of the display system. Potential applications for sunlight readable flexible and rollable displays are emphasized. (paper)

[en] Tunable optofluidic devices exhibit some unique characteristics that are not achievable in conventional solid-state photonic devices. They provide exciting opportunities for emerging applications in imaging, information processing, sensing, optical communication, lab-on-a-chip and biomedical engineering. A dielectrophoresis effect is an important physical mechanism to realize tunable optofluidic devices. Via balancing the voltage-induced dielectric force and interfacial tension, the liquid interface can be dynamically manipulated and the optical output reconfigured or adaptively tuned in real time. Dielectrophoretically tunable optofluidic devices offer several attractive features, such as rapid prototyping, miniaturization, easy integration and low power consumption. In this review paper, we first explain the underlying operation principles and then review some recent progress in this field, covering the topics of adaptive lens, beam steering, iris, grating, optical switch/attenuator and single pixel display. Finally, the future perspectives are discussed. (topical review)

[en] Submillisecond response times and low operation voltage are critical to next generation liquid crystal display and photonic devices. In this paper, we review the recent progress of three fast-response short-pitch cholesteric liquid crystal modes: blue phase (BP), uniform standing helix (USH), and uniform lying helix (ULH). This review starts with a brief introduction of device structures and working principles, and then highlights two competing electro-optical effects: dielectric effect and flexoelectric effect. Next, we compare their electro-optical behaviors, response time, temperature dependence, and contrast ratio. Based on our established simulation model, we are able to optimize the phase compensation scheme for improving the viewing angle and gamma shift of USH and ULH modes. Finally, we analyze some major challenges, which remain to be overcome before the widespread applications of these liquid crystal devices can be realized. (topical review)

[en] We report a back-cavity design to enhance the optical efficiency of a quantum dot light-emitting diode (QLED) or an organic light-emitting diode (OLED) for display and lighting applications. Our simulation results show that the back-cavity design exhibits two major advantages: (1) the transparent electrode helps to increase the transmittance of backward light despite using a semi-transparent metal electrode, and (2) the thickness of the low index optical buffer layer can be optimized to modify the proportion of each optical channel. The proposed back-cavity also helps to lower the refractive index of the high-index substrate from ∼2.0 to ∼1.8 for achieving high optical efficiency. Finally, the introduced back-cavity does not degrade the color performance of the QLED/OLED. (paper)

[en] Polymer-stabilized blue phase liquid crystal displays based on the Kerr effect are emerging due to their submillisecond response time, wide view and simple fabrication process. However, the conventional in-plane switching device exhibits a relatively high operating voltage because the electric fields are restricted in the vicinity of the electrode surface. To overcome this technical barrier, we propose a partitioned wall-shaped electrode configuration so that the induced birefringence is uniform between electrodes throughout the entire cell gap. Consequently, the operating voltage is reduced by ∼ 2.8x with two transistors. The responsible physical mechanisms are explained.

[en] An optically isotropic liquid crystal (LC) such as a blue phase LC or an optically isotropic nano-structured LC exhibits a very wide viewing angle because the induced birefringence is along the in-plane electric field. Utilizing such a material, we propose a liquid crystal display (LCD) whose viewing angle can be switched from wide view to narrow view using only one panel. In the device, each pixel is divided into two parts: a major pixel and a sub-pixel. The main pixels display the images while the sub-pixels control the viewing angle. In the main pixels, birefringence is induced by horizontal electric fields through inter-digital electrodes leading to a wide viewing angle, while in the sub-pixels, birefringence is induced by the vertical electric field so that phase retardation occurs only at oblique angles. As a result, the dark state (or contrast ratio) of the entire pixel can be controlled by the voltage of the sub-pixels. Such a switchable viewing angle LCD is attractive for protecting personal privacy.