Jian-Yu Liu

An Approach to the Design of Ferroelectric Liquid Crystals with Large Second Order Electronic Nonlinear Optical Susceptibility

Abstract Ferroelectric liquid crystal thin films in the Clark-Lagerwall surface-stabilized geometry exhibit well known spontaneous polar orientation of functional groups. The symmetry of the system thus allows the existence of bulk electronic second order nonlinear hyperpolarizability x(2) within thc context of the simple dipolar model. For all FLC materials examined to date, however, the magnitude of x(2) is small, presumably since the particular functional group arrays oriented along the polar axis possess small molecular hyperpolarizdbility β. Using the Boulder Model for the molecular origins of the polar order occurring in FLC films, it is possible to design materials with functionalized aromatic rings oriented along the polar axis of the film. Since such functional arrays may show respectable values of β, it should be possible to obtain FIX films (both low molecular weight and polymeric) with useful magnitude of x(2) using this approach. Results of initial experiments aimed at design of FLC materials...

The measurement of second‐harmonic generation in novel ferroelectric liquid crystal materials

We present the analysis of experimental results on second‐harmonic generation in a novel ferroelectric liquid crystal (FLC) material, o‐ nitroalkoxyphenyl biphenylcarboxylate 1, synthesized specifically for large nonlinear coefficients. All nonzero dij coefficients have been measured, with the largest being d22 = 0.6 ± 0.3 pm/V. Relative values of refractive indices are also given suggesting uniaxial optical properties with large birefringence (nz − nx≊ 0.20 at λ=1.064 μm). This material demonstrates the flexibility of FLC molecular synthesis to form thermodynamically stable macroscopically aligned materials for second‐order nonlinear optics applications.

High-speed wavelength tunable liquid crystal filter

We describe the first high-speed, continuously tunable liquid crystal optical filter suitable for wavelength division multiaccess (WDMA) optical networks. The filter utilizes chiral smectic A* electroclinic liquid crystal as the active cavity material in a Fabry-Perot etalon to obtain microsecond switching speed. Using the commercially available BDH764E liquid crystal material, we demonstrate a tunable optical filter with a switching speed of less than 10 /spl mu/s and a tuning range of approximately 30 nm, when the filter passband is centered at 1.55 /spl mu/m.<<ETX>>

Second-harmonic generation in ferroelectric liquid crystals.

We present phase-matched, second-harmonic generation in the ferroelectric liquid-crystal material SCE9 (manufactured by BDH Ltd.). From the analysis of these results, the absolute values of all nonzero components of the d tensor have been obtained. A direct comparison between this material and the most efficient ferroelectric liquidcrystal material reported so far (ZLI3654) is made, which shows that SCE9 is four times more efficient at frequency doubling. At the phase-matching angle (theta = 19.1 degrees ) a d(eff) of 0.010(1) x 10(-12) m/V is measured. The results are consistent with near uniaxiality, the extent of which has been determined from experimental data (n(y) - n(x) = 0.0003, n(2) - n(x) = 0.17).

High-speed liquid crystal fiber Fabry-Perot tunable filter

We report a liquid-crystal fiber Fabry-Perot tunable filter (LC-FFP-TF) with fast tuning (<33 /spl mu/s) over a 0.4-12 nm wavelength range centered at 1550 nm, at a temperature of 35/spl deg/C, using a commercially available electroclinic LC material, BDH764E. Typically, the fall time of the LC-FFP-TF is over an order of magnitude shorter than the rise time. For the first time to our knowledge, switching between two discrete wavelengths was demonstrated using an LC-FFP-TF.

High-speed analog refractive-index modulator that uses a chiral smectic liquid crystal

We demonstrate a fast liquid-crystal analog phase modulator composed of a homeotropically aligned electroclinic chiral smectic liquid crystal. Pure phase modulation is obtained by electrical modulation of the refractive index of the liquid crystal. A refractive-index change of 0.045 can be obtained at a 5-micros switching speed with a 15-V/microm applied electric field by use of the commercial electroclinic chiral smectic liquid crystal mixture BDH764E. This results in a pi phase modulation depth at lambda = 0.633 microm in a device of 10-microm thickness.

FERROELECTRIC LIQUID CRYSTAL FIBER WAVEGUIDE

Abstract In this paper, we present the results on the fabrication and characterization of the FLC-in-fiber waveguides, in which hollow core optical fibers with typical core diameters of 2 to 10 μms are filled with FLCs. Proper alignment of the FLC inside the fiber core, allows for the electro-optic modulation of the liquid crystal refractive index resulting in a new class of devices for optical communication and sensors. We describe the fabrication process of the FLC-in-fiber waveguides. The propagation loss is measured to be 3.5 dB/cm. Linear modulation of the tilt angle up to 10 degrees is obtained by applying the electric fields up to 5 volts/μm. And a 10/24 μsecs rise/fall time is demonstrated with an E-field of 1 volt/μm applied across a fiber of 1 cm in length.

Effective electromechanical moduli of ferroelectric ceramics with fiber textures

In this letter, we report the predictions on the effective piezoelectric coefficients and electromechanical coupling factors of ferroelectric ceramics BaTiO3 and Pb(Mg1∕3Nb2∕3)O3–PbTiO3 (PMN-PT) with various fiber textures, including [001], [011], and [111], using a two-scale micromechanical model that accounts for microstructural phenomena at both domain and grain levels. It was observed that for BaTiO3 the [011] texture is optimal with highest d31 and d33, while for PMN-PT [001] texture is optimal despite the fact that [011]-oriented single-crystalline PMN-PT has higher d32 than that of [001]-oriented PMN-PT single crystal. In fact, [011]-textured PMN-PT ceramics have much smaller piezoelectric coefficients d32 and d33 than does [011]-oriented PMN-PT single crystal. It is also noted that [001]-textured BaTiO3 and PMN-PT ceramics have even higher electromechanical coupling factor k31 than that of [001]-oriented single crystals.

Room temperature 10 MHz electro‐optic modulation in ferroelectric liquid crystals

We report high frequency (≳10 MHz) electro‐optic (EO) modulation using a chiral smectic C* ferroelectric liquid crystal (FLC). Results indicate that the r32 coefficient of the commercially available chiral smectic FLC SCE9 is ≊3 pm/V.

Liquid crystal fiber phase modulator

In the following, we present the fabrication techniques of the liquid crystal fibre phase modulator using liquid crystal fibre (LCF), working theory and measurement on the fiber phase modulation using LCF. We also present the measurement of the propagation loss of the LCF.