Published papers

Plastic GRIN Rods with various profiles of refractive-index distributions were successfully obtained by the photocopolymerization process. We propose a mechanism to form radial GRIN by photocopolymerization in multimonomer systems. By developing the computer program which calculates the physical conditions of polymer from the chemical structure, and which predicts the index profile of the GRIN rods on the basis of the above mechanism, the index profile of the GRIN rods fabricated were tightly controlled.

Plastic GRIN rod and fiber lenses have been fabricated by photocopolymerization of a ternary monomer system, methyl methacrylate-N-vinyl carbazole vinyl acetate. We now propose the general mechanism for forming radial GRIN in the ternary monomer system using computer simulation. The relationship between the preparation condition and the optical characteristics was clarified. The region having quadratic-index distribution and the numerical aperture were remarkably improved by the ternary monomer system.

The light-focusing rod (LFR) was prepared by the photocopolymerization of MMA with VPAC and VB, using BPO, BN, and BME as an initiator. The LFR with high transparency and steep refractive-index distribution was obtained using MMA-VPAc pair and BME. The difference in the index distributions under BPO, BN, and BME initiations was clarified in terms of the photoinitiation rate and the accompanying thermal polymerization during the photocopolymerization process. The light scattering intensity from the LFR was related to the heterogeneity of the copolymer composition and the compatibility between the M1 and M2 polymers. The comparison of the light scattering theory with the experimental data indicated that the much less scattering intensity from the MMA-VPAc LFR than the MMA-VB LFR should be attributed to the good compatibility between MMA and VPAc polymers, and scarcely attributed to the index difference between the VPAc and VB polymers.

The light-focusing plastic rod (LFR) and fiber (LFF) were fabricated by Photocopolymerization of MMA with VPAc. The MMA-VPAc LFR has much higher clarity than that of the MMA-VB LFR reported previously. Using the BME as the initiator, which initiates photopolymerization preferentially, led to a much steeper index distribution than using BPO, which initiates thermal- and photochemical polymerization simultaneously. The relationship between preparation condition and optical characteristics were clarified in terms of the index distribution, light scattering, lens function, and attenuation of light transmission.

A doubly-imaging fiber-lens (DIF) was fabricated by the Photocopolymerization of MMA with VB. The core and the outer portions of the DIF form two refractive-index distributions with different gradient-indexes from one another. The DIF, assuring a meridional ray under paraxial condition, led to a simple and feasible method estimating the index-profile of DIF on a basis of its lens function. The validity of this method was verified by the measurement in various conditions and the comparison with the index-profile determined interferometrically.

A light-focusing plastic fiber (LFF) with a parabolic refractive-index distribution was obtained by the continuous heat drawing of the preform prepared from the Photocopolymerization of MMA with VB. The relation between the preparation conditions and the optical and mechanical properties of the LFFs was clarified. The index profile of LFFs is found to be scarcely affected by the continuous heat drawing process compared with that of original preforms. The resulting LFF would be suitable for short-distance communication system due to its attenuation being higher than 103 dB/km.

The Photocopolymerization of MMA with VB containing BPO was carried out in a glass tube to fabricate a light-focusing plastic Rod (LFR, radius Rp) with a parabolic refractive-index distribution (distribution constant A) in the region near the center axis (radius Rc). The dependence of A and Rc/Rp on MMA/VB, BPO concentration and the velocity of the UV lamp was clarified. These relations could be explained using a computer simulation based on the polymerization mechanism.

Two analysis procedures to determine the refractive-index profile using Interphako interference microscopy are compared for accuracy: (I) express the profile as a five-nominal equation; (II) considering ray bending due to the index gradient and using Abel inversion. Computer simulation indicate that the errors of both procedures are comparable except for mismatching between the specimen periphery (np) and immersion oil (n2) where Analysis (I) is more accurate than Analysis (II). The partial splitting method is more practicable than total spotting for a rodlike specimen. In addition, improved partial splitting procedure facilitates reduction of error. The index profiles of the two selected light-focusing plastic rods (LFR) were calculated with these two procedures in various conditions. It is concluded that Analysis (I) is preferable to Analysis (II) when np≠n2 and that the improved partial splitting procedure is a practicable method for determining the index profile of LFR.

A novel TE-TM mode converter using optically active polymer: poly-l-menthylmethacrylate (PMtMA) was studied theoretically and experimentally. In a three-layered slab waveguide consisting of the PMtMA core layer on a fused quartz substrate, a low-loss TE0-TM0 mode conversion with an efficiency of 60 to 70% was easily obtained for the first time at a wavelength of 441.6 nm. The method to achieve a phase-matched operation of this polymer TE-TM mode converter was also discussed.

The optimum refractive-index distribution of the high bandwidth GI POF in which material dispersion is taken into account was clarified for the first time. Since modal dispersion remarkably decreased by GI POF, this paper focuses on the ultimate bandwidth achieved by POF, quantitatively estimating the material dispersion as well as modal dispersion. The results indicated that the bandwidth of the PMMA based GI POF was dominated by material dispersion when the required data rate becomes larger than a few GB/s. It was also confirmed that material dispersion strongly depends on the matrix polymer and that use of fluorinated polymer whose material dispersion is lower than that of PMMA allows for 10Gb/s signal transmission.

プラスチック材料を用いて屈折率分布型光学素子を作製する方法には幾つかあるが、この総説中では特に拡散現象を利用して屈折率分布を形成させる界面ゲル重合法とカーブドモールド法について示した。界面ゲル重合法はプラスチック光ファイバーに応用されており、高伝送帯域を有するファイバーが作製され、またカーブドモールド法では、大口径なレンズの作製に応用されている。

本稿では、癌のphotodynamic診断やphotodynamic治療光源として色素ドーププラスチック光ファイバー（DPOF)を用いる上での動作特性と光感受性物質に対する光化学作用の基礎特性を示す。波長560nm付近で出力が得られるRhodamine 6GドープPOFを光源とし、光感受性物質の亜鉛ポルフィリン化合物の光化学反応により、活性酸素の一種であるスーパーオキシドの発生をルミノール反応を用いて検出する。さらに医用デバイスDPOFの今後の可能性について論じている。

Laser-dye doped plastic optical fiber amplifier (POFA) is fabricated and its basic perfprmances are demonstrated. As doped dye, Rhodamine B (RB) is prepared. Output power os 1kW with a gain of 30dB can be obtained by using RB doped POFA at a concentration of 1ppm. The energy conversion efficiency, which is defined as output signal power normalized by lounched pump power, is 25%. Possibility of plastic optical fiber laser (POFL) is discussed by analyzing a rate equation of laser. It is proved that a RB doped POFL (core diameter ; 100µm, lengtth : 30mm) has high performance around 580nm. As one of the applications of POFA, photodynamic diagnosis (PDD) for medicine is proposed. Fluorecence from Zinc-Porphyrin is confirmed by a Rhodamine 6G doped POFA.

Basic characteristics of organic-dye doped polymer optical fibers (DPOFs) are demonstrated. The devices contain laser dye, such as Rhodamine 6G (R6G) and Rhodamine B (RB) in the core region. Firstly, amplification characteristics of DPOF amplifiers (POFAs) excited by a pulse-operated, doubled Nd:YAG laser are demonstrated, e.g., a 250mm-length of RB-POFA gives 1kW (30dB) of amplified signal at 591nm. Next, an all solid state system of RB DPOF laser (POFL) is discussed by numerical simulation and the experimental result of high-power amplified spontaneous emission (ASE) by strong excitation of DPOF is shown.

A very large GRIN polymer successfully prepared for the first time, to the best of our knowledge, by two methods: the curved mold method and the diffusion copolymerization method. Both methods gave a radial GRIN polymer with a diameter of 70mm and a Δn value greater than 0.02. Ray tracing through these radial GRIN polymers was used to predict that such a GRIN polymer could be a promising candidate for thinner ophthalmic lenses with no spherical aberration of multifocusing characteristics.

High power (620W) and high gain (28dB) amplification was achieved by a Rhodamine B (RB)-doped GI POFA with a 1-m length. A theoretical analysis of the amplification in the RB-doped GI POFA was carried out using the rate equation for the fast three-level system. The calculated gain behavior reasonably fit the experimentally data. The possibility of higher power (more than 620W) and higher gain (more than 28dB) amplification covering a wide range in the visible region is shown from the calculation. Absorption and emission cross section of RB in PMMA bulk were determined and used in the calculation. The values of the cross sections were approximately 10,000 times larger than those of ER3+ in GeO2-SiO2 glass.

We propose a new concept, highly scattered optical transmission (HSOT) polymer, which consists of specific microscopic heterogeneous structure, as a new light source medium. Therefore, the incident beam is efficiently converted to the homogeneous illumination from the surface of the HSOT polymer by effective scattering due to such heterogeneous structures. This HSOT polymer was applied to the LCD backlight that was simpler in system and more than 50% brighter than in a conventional transparent PMMA-based backlight system.

Organic dye-doped POFA are fabricated and their amplification characteristics are fabricated and their amplification characteristics are investigated. Rhodamine 6G, Rhodamine B, and Perylene Red are used as organic dyes for optical amplification. The amplification of optical signals at 571 nm, 591nm, and 621nm wavelength is confirmed through pumping by the second harmonic of a pulse-operated Nd: YAG laser. It is shown that very high output powers can be achieved by increasing the caliber of Rhodamine B doped POFA. One kW optical signal output (30 dB gain) is obtainable at dye doping of 1 ppm, 500-µm core radius, and POFA length of 250mm. The conversion efficiency of such a high output amplifier is 27%. The POFAs are advantageous over liquid-dye laser because they are easily handled. Multistage POFAs ins the form of joint POFAs are proposed as new light source and their oscillation characteristics are discussed.

医療分野で利用できるような、高強度のパルス光を、ポリマー光ファイバー増幅器を用いて発生させることに成功した。ここではその応用例を示した。

通信のための広帯域POFを中心に近年開発された光ファイバー増幅器についても解説した。