Submillisecond-response and scattering-free infrared liquid crystal phase modulators

We demonstrate a submillisecond-response and scattering-free infrared phase modulator using a polymer network liquid crystal (PNLC). The required voltage for achieving 2 pi phase change at lambda = 1.06 mu m is 70V (or 5.8 V/mu m) and the measured response time is similar to 200 mu s at 25 degrees C and 30 mu s at 70 degrees C. Opposite to our conventional understanding, a high viscosity LC helps to achieve small domain size during polymerization process, which in turn reduces the response time and light scattering. We use Rayleigh-Gans-Debye scattering model to analyze the voltage-on state transmission spectra. When the domain size is comparable to the wavelength, the model fits with experimental results well. But when the domain size is smaller than the wavelength, the simple Rayleigh model works well. (C) 2012 Optical Society of America