Switchable Bragg diffraction from liquid crystal in colloid-templated structures

– We have incorporated nematic liquid crystal into periodic, polymer host structures templated from self-assembled colloids. Using these composite materials, we demonstrate the first electrically switchable three-dimensional Bragg diffraction. The switchable beam deflection is potentially useful for non-mechanical beam steering and optical beam splitting devices. We compare the electro-optic response of our templated liquid-crystal/polymer composites with conventional polymer-dispersed liquid crystals (PDLCs). Our data reveal a qualitatively different and faster response for liquid crystal distributed within a connected cavity network, as compared to isolated liquid-crystal droplets within a polymer matrix. Rapid expansion of communications networks is driving intense research and development efforts in the field of optical switching [1]. As the transmission capacity of fibre optics lines continues to increase, new generations of components for handling communications traffic are required. In particular, to reduce cost and complexity it is desirable to develop beam steering schemes capable of re-routing optical signals arriving at a node to multiple destinations, without optical-to-electronic conversion. The possibility for these optical applications has stimulated tremendous interest in photonic crystals [2–4], and in combinations of photonic crystals with active materials [5–9]. In this report, we describe a class of liquid-crystal/polymer composites that offer the potential for efficient optical beam deflection via switchable Bragg diffraction. A variety of alternatives utilising both “solid-state” and “soft” materials have been explored for deflecting or switching optical beams. Solid-state devices for steering or high-speed modulation of light exploit acousto-optic beam deflection, non-linear optical crystals, or optically pumped carrier shifting in semiconductors [10–12]. Soft devices employ electro-optic or thermo-optic polymers, liquid crystals, and micro-structured composites [13–18]. Although they are generally slower than solid-state–based alternatives, soft-material devices are still