David Doroski

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...

Degradation of liquid crystal device performance due to selective adsorption of ions

Performance degradation in liquid crystal cells was studied by analyzing the time evolution of optical and integrated current vs voltage hysteresis curves as test cells were subjected to a dc bias. We find evidence for permanent increases in liquid crystal mobile ion populations, the primary cause of device performance degradation, and suggest this permanent increase is due to selective adsorption by the alignment layers of ions of a single charge sign combined with the presence of a neutral ionizable species in the liquid crystal.

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.

Continuously tunable smectic A* liquid-crystal color filter

A new continuously tunable color filter, which uses smectic A(*) liquid-crystal half-wave plates, is described and experimentally demonstrated. Multiple-stage Lyot filters with broad tunability and high finesse can be constructed with this design. The transmission characteristics of a single-stage filter, which is continuously tuned over 115 nm of the visible spectrum, are presented. Experimental results are compared with computer simulations, and they show excellent agreement. The advantages of the smectic A(*) liquid-crystal tunable filter over existing filter structures include low switching voltages (+/-30 V), rapid tunability (10 MHz), potentially high transmission, wide field of view, and large aperture.

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).

Infrared linear diattenuation and birefringence spectra of ferroelectric liquid crystals

Linear diattenuation and linear birefringence spectra of three ferroelectric liquid-crystalline materials, 764E, SCE4, and SCE9, are presented for the wavelength region from 2.5 to 12 microm. Relatively high birefringence (Deltan >/= 0.1) was found in the transmission bands from 2.5 to 3.2 microm and 3.6 to 5.7 microm, with only a small amount of interference from linear diattenuation (D </= 2%). The potential for these materials as broad-spectral-band infrared modulators in these regions is suggested by the relatively constant retardance and small linear di-attenuation. Substantially larger values of linear diattenuation and retardance are found in the narrower transmission bands beyond 5.8 microm. The linear diattenuation and linear birefringence spectra display the expected anomalous dispersion near the absorption bands.

Applications of binary and analog hydrogenated amorphous silicon/ferroelectric liquid-crystal optically addressed spatial light modulators

Analytical and experimental results that show novelty filtering, optical phase conjugation, and real-time edge enhancement by using optically addressed spatial light modulators that comprise amorphous silicon photodiodes and analog and binary ferroelectric liquid-crystal modulators are presented. The advantages of these devices for the above applications include high-speed, low-power operation and high spatial resolution.

ALIGNMENT LAYERS FOR IMPROVED SURFACE-STABILIZED FERROELECTRIC LIQUID-CRYSTAL DEVICES

Ultrathin silane monolayer and silicon oxide alignment layers in surface-stabilized ferroelectric liquidcrystal devices are shown to enhance bistability and reduce degradation from ions.

Rapidly switchable optical filter for color generation.

A ferroelectric liquid-crystal (FLC) color filter is described and experimentally demonstrated. The device consists of three polarizers and five smectic C* FLC cells. With the application of an appropriate electric field to each FLC cell, five outputs are observed. These consist of the three primary colors (red, green, and blue) along with white and black. With the rapid addressing speed of the FLCs, the FLC color filter can be used for color display applications, such as backlighting FLC television.

Tradeoffs in the design and operation of optically addressed spatial light modulators

We describe tradeoffs which are required in obtaining desired characteristics from a-Si:H/FLC optically addressed spatial light modulators. The tradeoffs involve material selection as well as operating device parameters.