Polymer-stabilized blue-phase liquid crystal (BPLC) has become an increasingly important technology trend for information display and photonic applications. BPLC exhibits several attractive features, such as reasonably wide temperature range, submillisecond gray-to-gray response time, no need for alignment layer, optically isotropic voltageoff state, and large cell gap tolerance when an in-plane switching (IPS) cell is employed. Fast response time not only suppresses image blurs, improves the overall transmittance but also enables color sequential display without noticeable color breakup. With time sequential RGB LED colors, the spatial color filters can be eliminated so that both optical efficiency and resolution density are tripled. High optical efficiency helps to reduce power consumption while high resolution density is particularly desirable for the future Ultra High Definition Television. However, some bottlenecks such as high operation voltage, hysteresis, low relaxation frequency, residual birefringence, image sticking, charging issue due to the large capacitance, and relatively low transmittance for the IPS mode, remain to be overcome before widespread application of BPLC can be realized. To reduce operation voltage, both new BPLC materials and new device structures have been investigated. In this paper, we highlight some recent advances in large Kerr constant, fast response time BPLC material development, and new device structures. Especially, we will focus on new BP LCDs with low operation voltage, submillisecond response time, high transmittance, and negligible hysteresis and residual birefringence. The sunrise for BP LCD is near.
We report a systematic photometric study of LCD based on quantum dot (QD) backlight, and find the optimal emission spectrum combination in terms of system efficiency and wide color gamut. A QD-based LCD has potential to achieve 120% AdobeRGB color gamut in CIE 1931 and 140% in CIE 1976 color space, while keeping the same energy efficiency as conventional backlights. Moreover, we present a transmissive color display based on voltage-stretchable liquid crystal droplet and quantum dot backlight. This polarizer-free display exhibits highly saturated colors, wide viewing angle and reasonably good contrast ratio. QD backlight allows LCD to display original colors with high fidelity, which makes LCD more competitive to organic LED. The prime time for QD-enhanced LCDs is near.
Polymer network liquid crystal (PNLC) is attractive for many photonic applications because of its fast response time and
large phase modulation. However, the voltage-on state light scattering caused by multi-domains of LC molecules hinders
its applications in the visible and near infrared regions. To reduce domain sizes and eliminate scattering for λ=1.06 μm
and 1.55 μm, we studied the effect of LC viscosity on domain sizes. PNLCs based on five different LC hosts were
prepared. The LC host was first mixed with 6% reactive mesogen and then filled into a 12-μm cell with homogeneous
alignment. After UV curing, we measured the on-state transmission spectra of these five PNLCs. By fitting the
transmission spectra with Rayleigh-Gans-Debye model, we can estimate the average domain sizes. We found that the
domain sizes of PNLC are inversely proportional to the rotational viscosity of the LC host. This finding can be explained
by the Stokes-Einstein equation. As a result, PNLC with a slower diffusion rate would cause smaller domain sizes,
which in turn lead to faster response time. To achieve a slower diffusion rate, we cured the PNLC samples at a lower
temperature. By selecting a high viscosity and high Δε LC host, we demonstrate a scattering-free (<3%) 2π phase
modulator at λ=1.06 μm and λ=1.55 μm. Temperature affects the PNLC performance significantly. As the operation
temperature increases from 25oC to 70oC, the response time drops from 220 μs to 30 μs. 2π operating voltage for λ=1.06
μm slightly increases from 65V to 85V. Meanwhile, hysteresis decreases from 7.7% to 2%. For λ=1.55μm, operating
voltage is 100V. If reflective mode is employed, operating voltage can be reduced to 55V.