Synthesis, Characterization And Application Of Polymer Materials For Optical Waveguide Devices

With the rapid development of microelectronics, optoelectronics, computing and communications, human society is gradually entering into an information age. However, due to the rapid increase of information, continuous requests have been made for the increase of speed, the enlargement of capacity and the decrease of cost of communications. Recently, organic polymer materials have been prepared and investigated by numerous scientists due to their tailorable optical properties such as refractive index and optical losses, and exhibit excellent mechanical and physical properties. We focused on the following three important aspects when synthesizing our waveguide polymer: first, high transparency at both 1310 nm and 1550 nm; second, high thermal and environmental stability; last, high refractive index controllability. The theory and development of these types of organic polymer materials for optical waveguide have been reviewed in chapter 1. And two things about polymer waveguide materials have been introduced respectively. One is the special property of polymer waveguide materials; the other is the type of the polymer for optical waveguide.In this dissertation, we can define three general approaches to achieving novel and high performance polymer for optical waveguide, such as crosslinkable Poly(MMA-CO-GMA), crosslinkable fluorinated polyester and fluorinated photoresist.In chapter 2, a novel crosslinkable Poly(methyl methacrylate-co-glycidyl methacrylate) have been synthesized and were determined by FT-IR, 1H-NMR spectrum, gel permeation chromatography (GPC),differential scanning calorimeter (DSC) and atomic force microscopy (AFM). The polymers have excellent film-forming capability and possess high glass transition temperature after crosslinking. The refractive index of the polymer can be adjusted between 1.483 and 1.588 at 1.55μm by doping bisphenol A epoxy. Because of three-dimensionally crosslinked structure, the birefringence of the polymers is very low. Arrayed waveguide grating, poly(MMA-co-GMA) acting as cladding and poly(MMA-co-GMA) doped bisphenol A epoxy acting as core layer, was fabricated by spin coating, using aluminum as mask and oxygen reactive ion etching. And its optical properties were characterized. The waveguide achieved single-mode transmission and optical loss of the core layer was less than 3.0 dB/cm at 1.55μm. On the basis of this work the low-loss polymers were prepared by copolymerization of 2,3,4,5,6-Pentafluorostyrene(PFS) and glycidyl methacrylate(GMA) via the sealed-tube reactive technique. Owing to their higher harmonic order, C-F overtones show extremely low absorption throughout the telecommunications windows. The waveguide achived single-mode transmission and optical loss of the core layer was less than 0.6dB/cm at 1.55μm.In chapter 3, A series of novel crosslinkable, highly fluorinated polyesters were synthesized by copolycondensation reactions of terephthaloyl chloride with 4, 4′-(hexafluoroisopropy-lidene)-diphenol and 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoro -octane-1,8-diol, followed by reaction with 2-hydroxyethyl methacrylate. The polyesters display excellent thermal stability, good adhesion on substrate and tunable refractive index. Furthermore, the polyesters can be thermally and photochemically crosslinked, which enable this kind of material to possess good chemical resistance and higher glass transition temperature. The resulting polyesters with the molecular weights (Mn: 12,100– 20,000 g mol-1) and polydispersities (1.49– 2.25) were useful for the fabrication of polymer optical devices due to their good solubility in common organic solvent and the processable flexibility. The ratios of the components of the polyesters were characterized by FTIR and NMR. The polyesters had high glass transition temperature (Tg: up to 170 oC) and good thermal stabilities (Td: up to 470 oC). The refractive index of the polyester film was tuned and controlled in the range of 1.447– 1.576 at 1550 nm by monitoring the component fractions during the preparation procedures. Low-loss optical waveguides were fabricated from the resulting polyesters and the propagation loss of the channel waveguides was measured to be around 0.56 dB/cm at 1550 nm.In chapter 4, a fluorinated bis-phenol-A novolac resin (FAR) for optical waveguide was synthesized based on 4, 4'-(hexafluoro-isopropylidene)diphenol, epoxy chloropropane and formadehyde. A negative fluorinated photoresist (FP) was made by composing of the FAR, diphenyl iodonium salt and solvent. The cross-linked material had good chemical resistance and thermal resistance. The film which was made by spinning coated the FP had good UV light lithograph sensitivity, large hardness and high glass transition temperature (Tg >170°C, after crosslinking). Low-loss optical waveguides with very smooth top surfaces were fabricated from the resulting FP by direct UV exposure and chemical development. Well-defined photolithography technique of the polymer was achieved in the presence of an appropriate photo acid generator and showed possibility for direct photolithography technique of waveguide structures. For waveguides without upper claddings, the propagation loss of the channel waveguides was measured to be 0.21 dB/cm at 1550 nm. In order to further improve the film forming property on various substrates, the photosensitive fluorinated resin with high molecular weight was synthesized. In addition to be used in the fabrication of waveguide devices by the same methods, its refractive index was adjusted by adding a fluorinated epoxy monomer.