Makoto Asai

High-Bandwidth Graded-Index Plastic Optical Fiber by the Dopant Diffusion Coextrusion Process

Today, the number of services, which includes large information contents like high-definition movies, is rapidly increasing. The graded-index plastic optical fiber (GI-POF) has been proposed as a solution. The conventional fabrication method of GI-POF, however, is unsuitable for mass production. Therefore, we propose the dopant diffusion coextrusion process for fabricating high-bandwidth GI-POF. It has been generally thought that formation mechanism of refractive-index distribution in optical polymer materials by this process would be a Ficks diffusion with constant diffusion coefficient and, therefore, has a tailing part at the core-cladding boundary. Contrary to predictions, we succeed in fabricating GI-POF with an almost optimum-index distribution. It is made evident by experiments and simulation that the formation mechanism of GI-POF by this process is a Ficks diffusion with diffusion coefficient dependent on dopant concentration. These results indicate high possibility of fabrication of high-bandwidth fibers of a polymethyl methacrylate-diphenyl sulfide system by the dopant diffusion coextrusion process.

Mechanical properties of tetra-PEG gels with supercoiled network structure

We investigate the effects of swelling and deswelling on the mechanical properties of tetra-polyethylene glycol gels with the precisely tuned polymerization degree of network strand (Nc) and polymer volume fraction at preparation (ϕ0) by varying the fraction of interest (ϕm). The ϕm-dependence of the elastic modulus exhibits a crossover at ϕc due to large contraction of the network strands (supercoiling) accompanying deswelling. The Obukhov model successfully describes the ϕm-dependence of the elastic modulus. We estimate the fractal dimension of network strands (Df) by analyzing the stress-elongation relationships at high stretching using Pincus blob concept. In the supercoiling region, Df increases with an increase in ϕm, which suggests that the gyration radius of network strands decreases with deswelling in affine manner. The extensibility increases with an increase in ϕm because the deswelling reduces the distance between the neighboring junctions. These findings will help to understand the structure and formation mechanism of supercoiling.

Poly(styrene)-based graded-index plastic optical fiber for home networks

We investigated poly(styrene) (PSt)-based graded-index plastic optical fiber (GI-POF) with low loss and high bandwidth for home networks. To install the GI-POF in home networks, the attenuation must be below 200 dB/km at a 670-680 nm wavelength, and the bandwidth must be over 2.0 GHz for the 50 m fiber. In this study, we selected a dibenzothiophene (DBT) as a dopant to PSt, and we fabricated PSt-DBT-based GI-POF. We confirmed that the PSt-DBT-based GI-POF has high bandwidth (4.4 GHz) for 50 m fiber and low loss (166-193 dB/km) at a 670-680 nm wavelength and obtained the GI-POF that satisfied the requirements for home networks.

Graded-index plastic optical fiber prepared by the coextrusion process.

A graded-index plastic optical fiber (GI POF) has been proposed as the transmission medium to realize high-speed information transmission. We have succeeded in fabricating a GI POF by the dopant diffusion coextrusion process, a method that allows continuous fabrication of GI POF. Although it has been indicated that the refractive index distribution of GI POF fabricated by this process is formed by Fick diffusion with the diffusion coefficient dependent on dopant concentration, the method to control it remains unknown. The purposes of this study are to establish the technology of stable fabricating of GI POF by the coextrusion process and to analyze the bandwidth.

High-Bandwidth Graded-Index Plastic Optical Fiber With Low-Attenuation, High-Bending Ability, and High-Thermal Stability for Home-Networks

The graded-index plastic optical fiber (GI-POF) is expected to be a communication medium for the next-generation optical home network because of its simple-to-use connection, installation, and high bandwidth. In spite of the expectation, we had a problem that a typical GI-POF using poly (methyl methacrylate) (PMMA) had high transmission loss in the expected communication wavelength band (VCSEL: 670-680 nm) for home networks; the required values of being below 200 dB/km could not be achieved. We, therefore, propose poly (2, 2, 2-trichloroethyl methacrylate) (PTCEMA) as a base material for the GI-POF. A PTCEMA-based GI-POF was fabricated, and its characteristics were evaluated. The PTCEMA is a prominent material in terms of its transparency and heat-resistant property. Our results demonstrated that the fabricated fiber surpassed the desired characteristics for the home network pertaining to attenuation and heat resistance. Specifically, the attenuation in the wavelength band (670-680 nm) was 104-136 dB/km, and the glass transition temperature (Tg) was 102°C in the core center where the Tg was at its lowest. Moreover, we confirmed that our PTCEMA-based GI-POF had sufficient mechanical strength and low bending loss. These results indicate that our novel GI-POF can be a candidate for home networks.

Novel Dopant for Graded-Index Polymer Optical Fiber with High-Thermal Stability

It is a challenging issue to develop a graded index polymer optical fiber (GI-POF) with sufficiently high thermal stability to be installed in the in-vehicle networks. Generally, a radial refractive index profile within the GI-POF is formed by adding a dopant to a polymer. This addition of the dopant significantly decreased the Tg of the polymer due to the plasticization. We demonstrated that 9-bromophenanthrene (BPT) had little plasticization on poly methyl methacrylate compared to conventional dopants, and propose the BPT as a potential dopant for the GI-POF.

Control of Refractive Index Distribution for High-Bandwidth Graded Index Plastic Optical Fiber

The graded index plastic optical fiber (GI-POF) has been proposed as the transmission medium to realize high-speed information transmission. We have succeeded in fabricating a GI-POF by the coextrusion process, a method that allows continuous fabrication of GI-POF. Although it has been indicated that the refractive index distribution of GI-POF fabricated by this process is formed by Fick diffusion with diffusion coefficient dependent on dopant concentration, the method to control it remains unknown. The purpose of this paper is to establish the technology of controlling refractive index distribution in GI-POF fabricated by the coextrusion process. Therefore, we investigate the physical mechanism of the dependency of diffusion coefficient on dopant concentration. It has become clear that the dependency is affected by the decrease of glass transition temperature and the nonlinear increase of melt flow rate. Moreover, through simulation of dopant diffusion by our originally developed program, it has become evident that changing the molecular weight of the core and cladding material allowed control of fabricating a GI-POF with optimal refractive index distribution by this fabrication method.

Preparation of graded-index plastic optical fiber by co-extrusion process

A novel fabrication method of graded index polymer optical fibers (GI-POFs) called the co-extrusion process is proposed and demonstrated for first time. This continuous fabrication process can reduce the fabrication cost of GI-POFs. Dopant diffusion temperature, dopant diffusion time, and the molecular weight of PMMA were optimized. By this optimization, desirable refractive index profile was achieved. Therefore, it is exhibited that the GI-POF obtained by the co-extrusion process has as high bandwidth as the one prepared by the conventional interfacial-gel polymerization process.

Surface Fluctuations Dominate the Slow Glassy Dynamics of Polymer-Grafted Colloid Assemblies

Colloids grafted with a corona layer of polymers show glassy behavior that covers a wide range of fragilities, with this behavior being tunable through variations in grafting density and grafting chain length. We find that the corona roughness, which is maximized for long chain lengths and sparse grafting, is directly correlated to the concentration-dependence of the system relaxation time (fragility). Relatively rougher colloids result in stronger liquids because their rotational motions become orientationally correlated across the whole system even at low particle loadings leading to an essentially Arrhenius-like concentration-dependence of the relaxation times near the glass transition. The smoother colloids do not show as much orientational correlation except at higher densities leading to fragile behavior. We therefore propose that these materials are an ideal model to study the physical properties of the glass transition.