Xiangdan Li

Low-loss and thermally stable TE-mode selective polymer waveguide using photosensitive fluorinated polyimide

A low-loss, thermally stable TE-mode selective optical waveguide was fabricated using a photosensitive fluorinated polyimide. The polymer undergoes photocrosslinking under UV exposure, thus changing its refractive index. The photocrosslinking-induced refractive index change was utilized to form channel waveguides. The propagation losses of the photosensitive fluorinated polyimide waveguides were less than 0.3 and 0.5 dB/cm for TE polarization at wavelengths of 1.3 and 1.55 /spl mu/m, respectively. The measured polarization extinction ratio was higher than 29 and 28 dB at wavelengths of 1.3 and 1.55 /spl mu/m, respectively. The refractive index of fluorinated polyimide film remains almost constant after being stored at 150/spl deg/C for 600 min.

Liquid crystal photoalignment material based on chloromethylated polyimide

We report a liquid crystal photoalignment material with high photosensitivity and excellent thermal stability. The chloromethylated aromatic polyimide exhibited defect-free homogeneous alignment of liquid crystals upon irradiation of polarized deep ultraviolet (UV) for 50s. The aligning ability of the film was retained up to 210°C, and the cell containing liquid crystals could be stored at 85°C for more than 14 days without any deterioration. FT-IR and UV–vis spectra confirmed that the alignment was induced by photodecomposition of polyimide, drastically accelerated by the introduction of chloromethyl side group.

Liquid crystal photoalignment using soluble photosensitive polyimide

A novel soluble fluorinated polyimide containing a photosensitive chalcone unit in the main chain was investigated as a thermally stable photoalignment material for liquid crystals. A defect-free homogeneous alignment of liquid crystals was induced on the surface of a polymer film after exposure to linearly polarized UV light at an exposure energy of 7200 mJ/cm2. Spectroscopic analyses revealed that [2+2] cycloadditon between the chalcone moieties generated the surface anisotropy needed to induce an efficient alignment of liquid crystals.

Zero-birefringence photosensitive polyimides for optical waveguides.

Zero-birefringence (delta n < 1 x 10(-6)) photosensitive fluorinated polyimides are synthesized for use in polymer optical waveguides. To obtain zero birefringence, the UV exposure time and copolymer content of photosensitive polyimides are controlled. Zero birefringence combined with photoprocessing of the material has excellent potential for applications in high-performance wavelength division multiplexing components such as polarization-independent arrayed waveguide gratings and Bragg wavelength filters.

Liquid-crystal photoalignment by photosensitive fluorinated poly(arylene ether)

We report a liquid-crystal (LC) photoalignment material with a high photosensitivity based on the fluorinated poly(arylene ether) containing a chalcone unit in the main chain. The fluorinated poly(arylene ether) exhibited defect-free homogeneous alignment of LCs upon irradiation of linearly polarized UV light for 10s. Spectroscopic analyses revealed that [2+2] cycloaddition between the chalcone moieties generated the surface anisotropy to induce an efficient alignment of LCs.

Preparation of photochromic cellulose derivatives containing spirobenzopyran

Abstract New cellulose acetate derivatives substituted with 6-(p-alkoxyphenyl)carbonyl-spirobenzopyran (COSP) were prepared from base-catalyzed etherification of cellulose acetate by 6-(p-bromohexyloxyphenyl)carbonylspirobenzopyran. The degree of COSP substitution was controlled by the feed amount of COSP and reached to max. 46 wt %. Tg of the resultant COSP bound cellulose (CA-COSP) was increased as the COSP substitution is increased. CA-COSP was soluble in aprotic polar solvents, to allow preparation of photochromic film by solution process. Reversible photochromic property was observed from the CA-COSP film by using two light sources of UV and visible light.

A New Polyimide with Multifunction of Alignment and Planarization

We developed new material, modified polyimide (MPI) that functions as both an alignment layer for the liquid crystal (LC) and a planarization layer (called overcoat (OC) layer) covering color filter layer. This functioning organic layer is very important to reduce process step and a cost when manufacturing in-plane switching (IPS) and fringe-field switching (FFS) devices since on top substrate of both devices, the alignment layer is coated over the OC layer. The MPI showed excellent aligning capability and high transparency with moderate degree of planarization. In addition, the fabricated twisted nematic LC cell showed similar electro-optic characteristics to those with conventional polyimide.

Novel Liquid Crystal Photoalignment System Based on New Soluble Polyimide

Novel liquid crystals(LCs)photoalignment system, which exhibits outstanding photosensitivity and excellent thermal stability, has been developed based on new soluble polyimide. Homogeneous alignment of liquid crystals(LCs)was induced by soluble polyimide(CMPI)having chloromethyl side groups upon irradiation of linearly polarized UV light(LPUVL)with short irradiation time. The photoaligned film was thermally stable without destroying LC alignment when LC cell was stored at 85°C for 14 days. The pretilt angle of LC decreased with irradiation time, which is contributed by the increased polar surface energy of CMPI film after irradiation of LPUVL. FT-IR spectra confirmed that the photosensitivity of polyimide was improved greatly by introducing chloromethyl group and the alignment of LC was contribute by the photo-decomposition of polyimide main chain upon irradiation.

Zero-birefringent polyimide for polymer optical waveguide

A novel zero birefringent and photosensitive polyimide was synthesized. The polymer is soluble in solvents and contains a chalcone group for photo-crosslinking by UV exposure. The glass transition and decomposition temperature of the polymer were 254°C and 430°C before cross-linking. Evolution of the absorption spectra upon UV exposure indicated that the cross-linking reaction is related to the cycloaddition of the double bonds in the chalcone group to form cyclobutane. The photo-crosslinking reaction not only increased the thermal stability, but also induced a refractive index change of the films. The refractive index of the film was reduced upon UV exposure from 1.5862 to 1.5697 for TE mode and from 1.5807 to 1.5697 for TM mode, respectively, resulting in zero birefringence after curing. Loss of p-conjugation in the chalcone group by the crosslinking reaction is supposed to induce the reduction of the refractive indices and orbital change from sp2 to sp3 makes the polymer chain be kinked, resulting in decrease of birefringence. The polymer film showed optical loss of 0.41 dB/cm at 1.3 mm and 0.54 dB/cm at 1.55 mm. Zero birefringence and low optical loss combined with photo-processibility of the material are making it an excellent candidate for the high performance waveguide materials.

Zero-birefringence photosensitive poly(arylene ether) for optical waveguides

Novel photosensitive fluorinated poly(arylene ether) containing chalcone unit (F-PAECh) in the main chain was synthesized from decafluorinated chalcone and fluorinated bisphenol at low temperature for polymer optical waveguide application. Upon UV irradiation on the resulting polymer film, [2+2] cycloaddition of chalocone moiety induced the anisotropic decrease of the refractive indices (nTE and nTM) accompanied with crosslinking of polymer film. The decrease was more significant in in-plane direction than out-of-plane direction, and consequently, zero birefringence was obtained with 4.5 min of exposure. Zero-birefringence as well as its excellent optical properties of F-PAECh makes it a promising candidate material for use in high-performance wavelength division multiplexing components such as polarization-independent arrayed waveguide gratings and Bragg wavelength filters.