Hyperbranched structures of chromophores were developed to improve the nonlinearity of optical polymers. Macromolecules with 3‐[p‐(2′‐hydroxyethylmethylamino)styryl]‐1‐dicyanomethylene‐5,5‐dimethylcyclohex‐2‐ene (AIDC) were prepared using 3,5‐dihydroxyphenyl groups as building blocks. When the molecule was incorporated into a polyimide backbone (PI‐DAIDC101), a high electro‐optic coefficient was obtained, giving 32 pm · V−1 at 1.55 μm. The nonlinearity is at least doubly enhanced in comparison with that of conventional side chain‐optical polyimides. This is mainly attributable to an increased polarizing efficiency derived from the chromophore structures.
Er-doped Al 2 O 3 -SiO 2 (1/9 in mol ratio of Al 2 O 3 /SiO 2 ) thin films were prepared by using a modified sol-gel process. The modified process entails the precipitation and digestion of Er(OH) 3 , obtained from the reaction between Er ions and NH 4 OH in solution. Thin films were deposited on Si wafers by using a spin coating technique (3000 rpm) and the coated films were heat treated at different temperatures for 1 h in an oxygen-purged furnace. All the films were structurally characterized by the X-ray diffraction technique using CuKa radiation. Refractive indices and the morphologies of the films were studied using a spectroscopic phase modulated ellipsometer and atomic force microscopy, respectively. It was observed that the films were crack free and of about 0.4 lm thickness in a single spin coating and both the lifetime and the photoluminescence intensity of Er ions increased with increasing the annealing temperature. The luminescence properties of the Er-doped Al 2 O 3 -SiO 2 made by a conventional and our modified doping process were compared and discussed from the stand point of peak intensities and lifetimes as a function of annealing temperatures. It is to be noted here that our modified process was found to be more effective in reducing the clustering of Er ions in Al 2 O 3 -SiO 2 materials as compared to that of the conventional method.
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Several sulfur-containing acrylate polymers were developed for a high refractive index with high transparency and good processing performance for thin films. A series of poly(methacrylate)s were synthesized by radical polymerization, in which thin films are coated on a quartz substrate for optical characterization. One, two and three sulfur atoms were bound into acrylate monomers and thermally copolymerized with methyl methacrylate. An alicyclic structure was used to achieve a dense molecular volume of the sulfur-containing monomer. Refractive index was measured under visible light. The index linearly increased with the sulfur-containing monomer content of the copolymer. Each homopolymer was predicted by an extrapolation method, resulting in a high refractive index of 1.624-1.725 at 589 nm. An Abbe's number of B30 was recorded for most sulfur polymers, indicating low wavelength dispersion of the index. A polymer with dipolar functionality displayed an Abbe's number of 40.9. High optical transparency of films was observed at the wavelengths of the index measurement. All polymers were thermally stable up to B250 1C and exhibited glass transition around 100 1C.
After synthesizing two chromophores with imine, we prepared acrylic nonlinear optical (NLO) polymers that contained the chromophores for all‐optical wavelength converters in optical fiber communication. The polymers show high d33, 35 pm · V−1, at 1.55 μm (pumping beam), considering their low losses, −3.0 dB · cm−1, at a wavelength of 0.785 μm (near second harmonic signal beam of the pumping beam). This result means that the polymers are good candidates for wavelength converters of an approximately 1.55 μm signal beam.
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