By introducing microfluidic plugs into interior fiber microchannels, we have developed a new category of active, tunable optical fiber. The positions and optical properties of the fluidic plugs can be directly controlled by utilizing actuators and pumps located on the fiber surface, thereby allowing the propagation characteristics of certain optical fiber modes to be usefully adjusted. These hybrid microfluidic/silica waveguides preserve the advantages of conventional, passive optical fiber, while at the same time providing versatile tuning capabilities. Examples of variable narrow and broadband all-fiber filters are described here. These fluidic fiber devices have the potential to be important technologies for next generation optical networks.
The existence of a helical symmetry axis is widespread in systems exhibiting liquid-crystalline order, especially in systems comprised of chiral molecules. Because these systems usually lack three-dimensional positional order, the helical symmetry axis cannot be observed using conventional x-ray scattering. Since the nature of the helical ordering determines the electro-optic response of the liquid crystal phases, it is a crucial structural feature to establish. Important for device applications are the various chiral smectic-C (SmC*) liquid crystal phases that are composed of fluid-like layers of tilted molecules. The electro-optic response of these phases varies from ferro to ferri to antiferroelectric. To elucidate the structure of the SmC* phases, we did resonant x-ray scattering at the sulfur K-edge on sulfur containing compounds. Our polarization-analyzed measurements of the resonant diffraction provided unambiguous evidence that the in-plane tilt direction in these phases exhibits a helical interlayer orientational ordering with a short pitch equals vd where d is the layer spacing. In the lowest temperature SmC* phase, which has antiferroelectric ordering, v was close to 2. At higher temperatures, the ferrielectric phases had v equals 3, then 4, and finally, an incommensurate value varying between 5 and 8 with increasing temperature.
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