Submicrosecond electro-optic switching in the liquid-crystal smectic A phase: The soft-mode ferroelectric effect

Abstract

A new liquid-crystal electro-optic modulating device similar to the surface-stabilized ferroelectric liquid-crystal device is described. It uses the same kind of ferroelectric chiral smectics and the same geometry as that device (thin sample in the ‘‘bookshelf ’’ layer arrangement) but instead of using a tilted smectic phase like the C* phase, it utilizes the above-lying, nonferroelectric A phase, taking advantage of the electroclinic effect. The achievable optical intensity modulation that can be detected through the full range of the A phase is considerably lower than for the surface-stabilized device, but the response is much faster. Furthermore, the response is strictly linear with respect to the applied electric field. The device concept is thus appropriate for modulator rather than for display applications. We describe the underlying physics and present measurements of induced tilt angle, of light modulation depth, and of rise time.

Macroscopic Torsional Strain and Induced Molecular Conformational Deracemization

“…The two substrates were then placed together to form a wedge: They were separated by respectively. θ 0 would be zero if there were no imposed twist, and the optical arrangement would correspond to the classical electroclinic geometry [13]. For θ 0 ≠ 0 the optical polarization approximately follows the relatively weak director twist (the Mauguin limit [8]) and the ordinary and extraordinary eigenmodes emerge from the cell rotated by ±θ 0 , with the sign depending on the sense of the twist.…”

“…1). The ac intensity I ac , its phase relative to E, and the dc intensity I dc were computer recorded as E rms was ramped upward with time over 500 s. Figure 2 shows ac dc / 4 I I -this corresponds to ϕ in the classical electroclinic geometry [13] -at ν = 1000…”

“…For θ 0 ≠ 0 the optical polarization approximately follows the relatively weak director twist (the Mauguin limit [8]) and the ordinary and extraordinary eigenmodes emerge from the cell rotated by ±θ 0 , with the sign depending on the sense of the twist. Hence, assuming n is parallel to the easy axes, the orientations of the analyzer nearly maintain the classical electroclinic geometry [13]. The output of the detector was fed into both a dc voltmeter and a lock-in amplifier that was referenced to the driving frequency ν of the ac electric field E applied across the LC (Fig.…”

Optics and electrooptics of chiral smectic C liquid crystals

“…Электроклинный эффект или эффект изменения под действием электрического поля угла наклона в смек тической А фазе вблизи температуры фазового пере хода в С*ЖК был впервые обнаружен Гаррофом и Мейером [9]. В дальнейшем появился ряд работ, по священных как исследованию электрооптических характеристик эффекта [55,118,119], тaк и разра ботке новых жидкокристаллических материалов для его реализации [120,121].…”

“…Зависимость наведенного полем угла наклона ди ректора от внешнего электрического поля в электро клинном эффекте имеет линейный характер [7,9,55,118,119]: где е с -Электроклинный коэффициент, определяе мый по формуле P = -наведенная поляризация ( -ди электрическая восприимчивость, -пьезомодуль), A = 2а(Т с -Т), а -эффективный модуль упругости по отношению к изменению угла наклона, Т -тем пература перехода в смектическую С* фазу. Согласно (58) электроклинный эффект имеет особенность в точ ке фазового перехода при Т = Т с .…”