Photo-Polymerization in Chiral Dopant Liquid Crystal Cells via Holographic Exposure to Fabricate Polarization-Independent Phase Modulator with Fast Optical Response.

Small liquid crystal domains with random director distributions were obtained to show novel optical isotropy using a holographic exposure processes to treat chiral dopant liquid crystal cells in the isotropic phase (i.e., polymer-stabilized isotropic liquid crystal cells). The cells used to fabricate phase modulators showed unique performances, including low light scattering, polarization-independence, and fast optical response. Furthermore, an extra fluoro-surfactant dopant in cells showed that the phase modulators retained their performance but with considerable reduction of operating voltages, from 180 Vrms to 100 Vrms.

Light distribution modulated diffuse reflectance spectroscopy.

Typically, a diffuse reflectance spectroscopy (DRS) system employing a continuous wave light source would need to acquire diffuse reflectances measured at multiple source-detector separations for determining the absorption and reduced scattering coefficients of turbid samples. This results in a multi-fiber probe structure and an indefinite probing depth. Here we present a novel DRS method that can utilize a few diffuse reflectances measured at one source-detector separation for recovering the optical properties of samples. The core of innovation is a liquid crystal (LC) cell whose scattering property can be modulated by the bias voltage. By placing the LC cell between the light source and the sample, the spatial distribution of light in the sample can be varied as the scattering property of the LC cell modulated by the bias voltage, and this would induce intensity variation of the collected diffuse reflectance. From a series of Monte Carlo simulations and phantom measurements, we found that this new light distribution modulated DRS (LDM DRS) system was capable of accurately recover the absorption and scattering coefficients of turbid samples and its probing depth only varied by less than 3% over the full bias voltage variation range. Our results suggest that this LDM DRS platform could be developed to various low-cost, efficient, and compact systems for in-vivo superficial tissue investigation.

Holographic polymer networks formed in liquid crystal phase modulators via a He-Ne laser to achieve ultra-fast optical response.

The holographic polymer network formed in liquid crystal (LC) phase modulators via a He-Ne laser in this study demonstrates ultra-fast optically response and low light scattering. These advantages are mainly caused by the small LC domains and uniform polymer network when processing LC cells via holographic exposure to a He-Ne laser. The use of this method to fabricate LC cells as phase modulators results in a decay time of 49 µs under 2π phase modulation at room temperature. The predicted fast optical response can be achieved when operating devices at high temperatures.

Using photopolymerization to achieve tunable liquid crystal lenses with coaxial bifocals.

Liquid crystal (LC) lenses with circular hole-patterned electrodes possess the excellent capabilities of tunable focal lengths. In this paper, we demonstrate the performance of a specific LC lens with tunable coaxial bifocals (CB) synthesized via photopolymerization of LC cells. The characteristics of tunable CB are clearly exhibited when the voltage applied is continuously increased, eventually disappearing until only one focus is left when significantly higher voltages are applied. We simultaneously demonstrate two types of tunable CB LC lenses fabricated via different photocurable processes and determine their optical functions.

Preventing occurrence of disclination lines in liquid crystal lenses with a large aperture by means of polymer stabilization.

Liquid crystal (LC) lenses with a circularly hole-patterned electrode possess excellent characteristics in optical performance, especially for the capability of tunable focal lengths. But, non-uniformly symmetrical electric fields in LC lenses usually induce disclination lines when operating. In general, the occurrence of disclination lines not only degrades their optical capability such as imaging performance, but also spends more time for tuning focal lengths. In this paper, we use a way of polymer stabilization to successfully prevent the disclination lines in LC lenses. Even arbitrarily adjusting the applied voltages in LC lenses, it seems no occurrence of disclination lines again. In addition, we compare the basic optical performance for LC lenses with or without polymer stabilization. From experimental results, it shows that they almost have the same optical performance.