Enhanced orientational Kerr effect in vertically aligned deformed helix ferroelectric liquid crystals

Abstract

We disclose the vertically aligned deformed helix ferroelectric liquid crystal whose Kerr constant (Kkerr≈130 nm/V2 at λ=543 nm) is around one order of magnitude higher than any other value previously reported for liquid crystalline structures. Under certain conditions, the phase modulation with ellipticity less than 0.05 over the range of continuous and hysteresis-free electric adjustment of the phase shift from zero to 2π has been obtained at subkilohertz frequency.

Electro-Optical Modulation in Planar Aligned Ferroelectric Liquid Crystals with Subwavelength Helix Pitch

“…3, b. This phenomenon can be explained by the birefringence dispersion of the liquid crystal, on the basis of the approaches developed earlier in [10,11,15,18], according to which the helical nanostructure of the DHFLC cell in the optical sense is equivalent to the ellipsoids of the refractive indices shown in Fig. 1.…”

“…Pure phase modulation of light, when the phase shift can be smoothly tuned from zero to 2π in electric field E at frequency around 1 kHz or more and without any essential change of the light ellipticity, is required for development of such modern photonic devices. These requirements can be satisfied using vertically aligned deformed helix ferroelectric liquid crystal (VADHFLC) with sub-wavelength helix pitch [10,11], under conditions illustrated in Figure 1 a b c Fig. 1.…”

“…Left: at E = 0, the field-free effective ellipsoid is uniaxially anisotropic with the principal optical axis parallel to the helix axis. Right: applying an in-plane electric field E  Y, makes the optical anisotropy biaxial with the two optical axes rotated by the angle Ψ d  E about the electric field vector E [10,11], c -is an illustration of the VADHFLC principal axis (PA) deflection due to deformation of the helix with the pitch p 0 in the presence of electric field…”

“…1, b, c) then no change of the light ellipticity happens because the PA deflection plane coincides with the light polarization plane in the same manner as for S-and B-effects in nematic liquid crystals, which are in use for manufacturing of photonic devices with the pure phase modulation of light. But characteristic frequencies of S-and B-cells are several tens of Hz, while of VADHFLC is about 1 kHz [3,10,11]. Thus, VADHFLC in principle has greater applications potential compared with S-and B-effects in nematic liquid crystals for development of photonic devices, where the pure phase modulation of light is required.…”

Electrically controlled phases of partially polarized light and orientational Kerr effect in liquid crystal ferroelectrics

“…However, most of the FLC modes are not suitable for phase-only modulation devices because their optical axis sweeps in the plane of the cell substrate producing undesirable changes in the polarization state of the incident light. In order to get around the optical axis switching problem the system based on the orientational Kerr effect in a vertically aligned deformed helix ferroelectric LC (DHFLC) with subwavelength helix pitch was suggested in [1,2]. In the geometry of a uniform lying helix, phase modulation of light in DHFLC cells was also studied using the experimental technique based on a Mach-Zehnder two-arm interferometer [3].…”