Keun-Byoung Yoon

Optical backplane system using waveguide-embedded PCBs and optical slots

As discussed in this paper, a practical optical backplane system was demonstrated, using a waveguide-embedded optical backplane board, processing boards, and optical slots for board-to-board interconnection. A metal optical bench was used as a packaging die for the optical devices and the integrated circuit chips in both the transmitter and the receiver processing boards. The polymer waveguide was produced by means of a hot-embossing technique and was then embedded following a conventional lamination processes. The average propagation loss of these waveguides was approximately 0.1 dB/cm at 850 nm. The dimension and optical properties of the waveguide in an optical backplane board were unchanged after lamination. As connection components between transmitter/receiver processing boards and an optical backplane board, optical slots were used for easy and repeatable insertion and extraction of the boards with a micrometer-scale precision. A 1/spl times/4 850-nm vertical-cavity surface-emitting laser array was used with 2 dBm of output power for the transmitter and a p-i-n photodiode array for the receiver. This paper successfully demonstrates 8 Gb/s of data transmission between the transmitter processing board and the optical backplane board.

Polyethylene/MMT nanocomposites prepared by in situ polymerization using supported catalyst systems

Abstract A polyethylene/montmorillonite(MMT) nanocomposite was prepared by in situ polymerization method using MMT-supported methylaluminoxane(MAO) cocatalyst and/or Cp2ZrCl2 catalyst. The catalyst components had been supported on the unmodified MMT-Na and modified commercial product, Cloisite 25A. With XRD it was found that the layered silicate gallery of Cloisite 25A was exfoliated by incorporating MAO cocatalyst and zirconocene catalyst while the d-spacing of MMT-Na was less changed. The in situ polymerization of ethylene was carried out to prepare the nanocomposite by using the supported MMT, and the fully exfoliated product was obtained with Cloisite 25A. The decomposition temperature of the obtained nanocomposite increased up to 25 °C, but the melting temperature was not improved much.

Fabrication of polymer photonic crystals using nanoimprint lithography

Dense two-dimensional periodic photonic bandgap structures are produced in poly(methyl methacrylate) thin films using nanoimprint lithography (NIL). The stamp original was made by electron beam lithography. Then, a high versatility of the process was achieved by fabricating copies of the stamp original via NIL, which enables varying and optimizing both fill factors and aspect ratios independently. For reliable stamp copying over the whole structural areas, the nanorheological behaviour had to be considered. Using those stamp copies, polymeric photonic band gap structures with an aspect ratio as high as 2 were successfully replicated.

Copolymerizations of olefins and dienes with homogeneous and heterogeneous catalysts

Abstract Copolymerizations of olefins (ethylene and propylene) and dienes were carried out with homogeneous [Et(Ind)2ZrCl2] and heterogeneous (Solvay-type TiCl3) catalysts, and the polymerization behaviors such as catalytic activity, copolymer composition and structure were examined in connection with catalyst type. Various dienes such as isoprene, 2-methyl-1,4-pentadiene, 2-methyl-1,5-hexadiene, 7-methyl-1,6-octadiene, 1,7-octadiene and 1,9-decadiene were used. Diene content of propylene copolymer obtained with Solvay-type TiCl3 catalyst was higher than that with Et(Ind)2ZrCl3. The prepared propylene/diene copolymer and polypropylene were treated with maleic anhydride (MAH) for modification. The content of grafted MAH in polypropylene chain increased to a great extent by incorporation of diene.

Investigation of the polymerization behavior of polysiloxane‐bridged dinuclear zirconocenes as model compounds for a heterogenized metallocene at the silica surface

The polymerization of ethylene was studied by using a series of polysiloxane-bridged dinuclear zirconocenes [(SiMe 2 O) n SiMe 2 (C 5 H 4 ) 2 ][(C 9 H 7 )ZrCl 2 ]2 (7, n = 1; 8, n = 2; 9, n = 3), the corresponding mononuclear zirconocene (C 5 H 5 )(C 9 H 7 )ZrCl 2 , 10, and the pentamethylene-bridged dinuclear zirconocene [(CH 2 ) 5 (C 5 H 4 )2][C 9 H 7 )-ZrCl 2 ] 2 , 13. From the polymerization studies using these catalysts it was found that (i) activities of the polysiloxane dinuclear zirconocenes 7-9 were lower than that of the corresponding mononuclear zirconocene 10, (ii ) molecular weights of polyethylenes produced by the dinuclear metallocenes are greater than that of polyethylene produced by the mononuclear metallocene, (iii) the complex 9 holding the longest bridging ligand exhibited the highest activity but produced a polymer having the smallest molecular weight among the polysiloxane-bridged dinuclear zirconocenes, and (iv)the pentamethylene-bridged dinuclear metailocene 13 showed higher activity than the complexes 7-9 and the mononuclear zirconocene 10. The formation of the lowest molecular weight of polyethylene by 9 was attributed to the influence of electron withdrawal caused by the Lewis acid-base interaction between the acidic aluminum of the cocatalyst and the basic oxygen at the polysiloxane linkage as well as the lack of a steric problem. An increase in steric congestion around the metal center led to not only a decrease in catalytic activity due to preventing facile monomer access to the active site but also an increase in the molecular weight of polyethylenes due to supressing β-H elimination.

Nanopatterning of photonic crystals with a photocurable silica–titania organic–inorganic hybrid material by a UV-based nanoimprint technique

UV patternable high refractive index inorganic–organic hybrid materials prepared by sol–gel process can be nanoimprinted in order to get photonic crystal nanopatterns. Non-hydrolytic sol–gel process can make a UV curable and relatively high refractive index hybrid material, which can be cured without a significant shrinkage for nanoimprinting. Sol–gel process of heterogeneously functionalized silicon alkoxides can make the organically modified inorganic Si–O–Ti network very well. The UV-based nanoimprint technique utilizes transparent templates and UV curable high refractive index materials to allow pattern replication at room temperature and very low pressure. UV-based nanoimprint technique is an efficient way to fabricate this sort of polymeric photonic crystal nanostructures.

Passive alignment method of polymer PLC devices by using a hot embossing technique

A novel fabrication process using a hot embossing technique has been developed for micromechanical passive alignment of polymer planar lightwave circuit (PLC) devices. With only one step of embossing, single-mode waveguide straight channels and micropedestals for passive aligning are simultaneously defined on a polymer thin film with an accuracy of /spl plusmn/0.5 /spl mu/m. This process reduces the steps for fabricating alignment structures. A fabricated polymer PLC chip and fibers are combined on a v-grooved silicon optical bench (SiOB) in a flip-chip manner. The process provides a coupling loss as low as 0.67 dB per coupling face and a cost-effective packaging solution for various polymer PLC devices.

Fabrication of Multimode Polymeric Waveguides by Hot Embossing Lithography

The fabrication of polymeric waveguides and the loss of waveguides were investigated for optical interconnection. Multimode polymeric waveguides were fabricated by hot embossing process. The replication of waveguide channels with hot embossing technology is of interest for single step processes that have to deliver a surface roughness far below the wavelength. Resulting waveguides exhibited a smooth surface profile and the square cross section of the core. The average propagation loss of these waveguides was approximately 0.2 dB/cm at 850 nm wavelength.

Board-to-board optical interconnection system using optical slots

A practical optical backplane system was prepared with transmitter-receiver processing boards and an optical backplane made of polymeric-waveguide-embedded optical printed-circuit boards. As connection components between the transmitter-receiver processing boards and backplane board, optical slots were used to enable easy and repeatable insertion and extraction of the boards with micrometer precision. We report an 8-Gb/s data transmission between transmitter processing board and optical backplane.

Fabrication and characterization of collagen-immobilized porous PHBV/HA nanocomposite scaffolds for bone tissue engineering

The porous composite scaffolds (PHBV/HA) consisting of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and hydroxyapatite (HA) were fabricated using a hot-press machine and salt-leaching. Collagen (type I) was then immobilized on the surface of the porous PHBV/HA composite scaffolds to improve tissue compatibility. The structure and morphology of the collagen-immobilized composite scaffolds (PHBV/HA/Col) were investigated using a scanning electron microscope (SEM), Fourier transform infrared (FTIR), and electron spectroscopy for chemical analysis (ESCA). The potential of the porous PHBV/HA/Col composite scaffolds for use as a bone scaffold was assessed by an experiment with osteoblast cells (MC3T3-E1) in terms of cell adhesion, proliferation, and differentiation. The results showed that the PHBV/HA/Col composite scaffolds possess better cell adhesion and significantly higher proliferation and differentiation than the PHBV/HA composite scaffolds and the PHBV scaffolds. These results suggest that the PHBV/HA/Col composite scaffolds have a high potential for use in the field of bone regeneration and tissue engineering.