We have explored a new doping method, which could disperse densely dyes into polymers, and have developed the present method into preparation of polymeric devices, such as storage media, luminescent media, switching devices, and waveguides. Preparation of the waveguide was based on dispersal of organofluorine (OF) compounds with a low refractive index in a polymer plate functioning as a cladding layer. The layer dispersed with the OF compound showed uniform concentration of the OF compound independent of the dispersal depth indicating that dispersion behavior was not governed by Fick's law. This means that the waveguide in the present study is step index. As a further development, we expanded the present method to preparation of a polymeric optical amplifier (POA) because reduction in intensity of a signal beam is clear due to driving of splitters in a short distance network using polymer optical fibers with large cores. A laser dye was dispersed densely within the core by the present method, followed by the dispersal of the OF compound to form the cladding layer resulting in the fabrication of POA with the large core. Amplification of the signal beam at 650 nm was confirmed in the waveguide upon irradiation of a pulsed laser.
We have developed a dye-doping process into a polymer, termed the "vapor transportation method." This method enables us to prepare a favorable doped layer in the polymer, possessing both a uniform dye concentration and a smooth surface. As one of developments of the vapor transportation method, we expanded to preparation of the optical waveguide. In preparation of the waveguide, low-molecular weight compound (phenyl benzoate; PB) showing the higher refractive index was dispersed in a matrix polymer (poly (methyl methacrylate), PMMA) through a mask by the developed method. After dispersion, the mask was removed, and another PMMA plate was put on doped PMMA by
vacuum press. A double-layered structure of the doped and non-doped regions was observed in the cross section, further, two regions described were transparent. It was confirmed that a beam incident on the edge of the doped region of the prepared sample emerged from the other edge, indicating that the doped regions acted as a core. The core radius (depth of the doped region) increased with treatment time and treatment temperature. Furthermore, refractive index of the core was controlled by treatment temperature. The fabricated waveguide showed the propagation loss of 0.47 dB/cm at 650 nm.
We have developed a simple process method, "vapor transportation method", for surface treatments and functionalization of polymeric materials. The method is addition of versatile functions to the solid polymeric materials with treatment of vapors under vacuum. Polymeric waveguides can be easily fabricated using the method. Exposing rods of transparent polymer, poly(methylmethacrylate) (PMMA), by vapor of organofluorine compounds, fluorinated esters, with lower refractive indices made the organofluorines dispersed into the PMMA from the surface. The refractive index of the organofluorine-doped PMMA surface was decreased and a cladding layer was formed. The core was the central part of the rod, which was the PMMA without dispersion of organofluorines. The properties of the waveguides made by the method were characterized. The refractive index and thickness of the cladding layer can be controlled by conditions of vapor transportation, such as treatment time and temperature.
The "vapor transportation method" with vacuum technique, developed previsouly in our laboratory, was used to form polymer thin layers with densely dispersed photochromic dyes on polystyrene (PS), poly(methyl methacrylate) (PMMA), and polymcarbonate (PC) substrates. The organic photochrmoic dye cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethane (CMTE) was used, and the rate of formation of the CMTE-conatining layer was as follows: PS > PC > PMMA. These observations are important for application of the present method to the formation of organic memory media for optical recording etc. These results also indicate that the formation rate is dependent on not only the chemical composition and the structure of the polymer substrate, but also on the treatment temperature. Optical density measurements of the CMTE-dispersed thin polymer films showed maximum values near the glass transition temperature (g) with increases in temperature of film formation. The Tg values of CMTE-dispersed polymers decreased rapidly after CMTE-dispersal into the polymer matrices, indicating that Tg values of the polymers are important parameters for investigation of the mechanism of formation of CMTE-dispersed layers on polymer substrates using the present method.
Three kinds of distyrylbenzene derivatives (DSB-1 -3 and -5) which are trimers of p-phenylenevinylene unit were vapor- deposited on a highly oriented PPV friction-transferred layer. Their structural and optical properties in thin film were investigated by transmission electron microscopy (TEM), atomic force microscopy (AFM) and ultraviolet-visible (UV- VIS) spectroscopy. DSB derivatives grew pseudo- homoepitaxially on a PPV friction-transferred layer. The molecular axes of DSB-1 and -3 were oriented parallel to the sliding direction of PPV. On the other hand, DSB-5 molecules adsorbed obliquely to the substrate surface. The polarized absorption spectra of DSB-1 and -3 films indicated remarkable anisotropic features. The dichroic ratios of absorption intensity (I(parallel)I(perpendicular)) were estimated to be 10 and 12 for DSB-1 and -3 films, respectively. The enhanced anisotropic properties were discussed based on the molecular orientation in the film.
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