Guided-Wave Liquid-Crystal Photonics

In this paper we review the state of the art in the field of liquid-crystal tunable guided-wave photonic devices, a unique type of fill-once, molecular-level actuated, opto-fluidic systems. These have recently attracted significant research interest, as potential candidates for low-cost, highly functional photonic elements. We cover a full range of structures, which spans from micromachined liquid-crystal on silicon devices to periodic structures and liquid-crystal infiltrated photonic crystal fibers with an eye on key-applications for photonics. Various approaches on the control of the LC molecular orientation are assessed, among which electro-, thermo- and all-optical switching. Special attention is paid to practical issues regarding liquid-crystal infiltration, molecular alignment and actuation, low-power operation, as well as their integrability in chip-scale or fiber-based devices. Finally, an extensive review of recent development in long range surface plasmon polariton waveguides, switches and directional couplers tuneable by means of liquid crystals is given.