94 research outputs found
Stable oscillating nonlinear beams in square-wave-biased-photorefractives
We demonstrate experimentally that in a centrosymmetric paraelectric
non-stationary boundary conditions can dynamically halt the intrinsic
instability of quasi-steady-state photorefractive self-trapping, driving beam
evolution into a stable oscillating two-soliton-state configuration.Comment: 3 pages, 4 figs, revtex os
Formation of a Silicate L 3 Phase with Continuously Adjustable Pore Sizes
the magnitude of the gain. Thus, the delay time of Ďł0.5 s observed in REFERENCES AND NOTES ___________________________ Since the demonstration that surfactants could be used in the fabrication of silica mesophases (1), amphiphiles have been used to produce inorganic materials with a variety of mesomorphic structures, including lamellar, hexagonally packed tubular, and cubic forms (2-12). Surfactant-induced assembly of inorganic structures is now recognized as a way to make novel nanoporous materials with larger pore sizes than was previously possible. However, techniques developed thus far have limited capability to produce very large pores of a predetermined size. Here we describe the synthesis and characterization of a new, random, bicontinuous silicate mesomorph for which predetermined pore sizes, over a very large size range, may be obtained. Most procedures for forming mesoporous silicates rely on the micelle-forming properties of a surfactant, typically at a low surfactant concentration. The addition of an inorganic precursor, such as an alkoxysilane, leads to association and coassembly into a mesophase precipitant whose structural dimensions are controlled by the surfactant length. Polymerization of the inorganic precursor and removal of the surfactant results in a rigid silica shell conforming to the structural shape of the mesophase. However, the use of dilute surfactant solutions limits the ability to predict the topology of the mesophase. Also, the typical product of the process is a powder of micrometer-sized particles, thereby limiting uses in filtration, optical, or electronic applications, where large-area thin films or large uniform monoliths of material are required. Finally, the pore volume is filled with surfactant; that is, the surfactant must be removed before the pores can be accessed. These difficulties may be partially avoided by the use of high-concentration surfactant systems in which either the inorganic precursors minimally perturb a preexisting surfactant-water liquid crystalline (LC) structure or the LC nature of the system may be recovered under appropriate experimental conditions, as shown by Attard et al. (6). Also, because the inorganic precursor does not precipitate out of solution, the resultant material conforms to the shape of the container in which it forms, thereby allowing fabrication of large monoliths of a desired size and shape. However, even in these cases, the pore size is limited by the surfactant and the limited range of compositions on the phase diagram for a given mesomorphic structure. Applications of silicate mesophases as filtration media, optical materials, and nanocomposites would be facilitated if th
Near-infrared sensitivity enhancement of photorefractive polymer composites by pre-illumination
Among the various applications for reversible holographic storage media, a particularly interesting one is time-gated holographic imaging (TGHI). This technique could provide a noninvasive medical diagnosis tool, related to optical coherence tomography. In this technique, biological samples are illuminated within their transparency windowwith near-infrared light, and information about subsurface features is obtained by a detection method that distinguishes between reflected photons originating from a certain depth and those scattered from various depths. Such an application requires reversible holographic storage media with very high sensitivity in the near-infrared. Photorefractive materials, in particular certain amorphous organic systems, are in principle promising candidate media, but their sensitivity has so far been too low, mainly owing to their long response times in the near-infrared. Here we introduce an organic photorefractive material—a composite based on the poly(arylene vinylene) copolymer TPD-PPV—that exhibits favourable near-infrared characteristics. We show that pre-illumination of this material at a shorter wavelength before holographic recording improves the response time by a factor of 40. This process was found to be reversible. We demonstrate multiple holographic recording with this technique at video rate under practical conditions
Court of Justice of the European Communities
: Encoding/decoding of FFH-OCDMA signals from 16 users is performed with Bragg grating arrays. Transmission of the multiplexed signals is demonstrated over 80 km of standard fiber at data rate exceeding 1 Gbit/s using dispersion compensating modules. 2000 Optical Society of America OCIS codes: (060.4510) Optical communications, (060.2340) Fiber optics components 1
Two-wave mixing and subharmonic instability in photorefractive materials
SIGLEAvailable from British Library Document Supply Centre- DSC:D186298 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
Analytical modeling of two beam coupling during grating translation in photorefractive media
Rotational diffusion model of orientational enhancement in AC field biased photorefractive polymers
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