Published papers

インターネット加入者の爆発的増加とともに、オフィス・家庭内においても数百Mbit/s以上の高速データ通信の要求が高まってきており、このような、中・短距離通信網に対しても高速光ネットワークインライフを構築する事が望まれている。この高速ネットワークメディアとして世界規模で検討が進められている石英系光ファイバは、コア径が数µm程度であるためにシステム構築に関してのコスト面が大きな問題となっている。これに対して、本稿では、近年注目を集めている大口径、低損失、広帯域ポリマー光ファイバ(POF)の現状と今後の展開についてまとめた。

Neodymium, praseodymium and erbium ions are successfully incorporated into the core of deuterated polymer-based optical fibers. The spectra of three fibers have several strong absorption bands in the visible and infrared regions. The fluorescence lifetime at 1060nm of Nd-chelate doped POF with an uncooled photodiode is obtained.

Photosensitivity in a perfluoropolymer (CYTOP) optical fiber is investigated. Significant diffraction has been observed from transmission gratings made from the fiber. A maximum diffraction efficiency of 1.6% has been achieved corresponding to an index change ≏3/10000. This study demonstrates for the first time the existence of significant photosensitivity and the feasibility of writing Bragg grating in CYTOP fiber.

Plastic optical fiber (POF) which has distinguished features such as high bandwidth, low loss like silica optical fiber and easy handling similar to copper cable, is expected to be a high speed network medium. It has been reported that the GI POF enabled gigabit data transmission. Furthermore, it was also confirmed that higher bandwidth than silica base multimode fiber can be achieved by the perfluorinated polymer base GI POF because of the small material dispersion. In this paper, the recent development of the GI POF is described in detail.

Plastic optical fiber (POF) which has distinguished features such as high bandwidth, low loss like silica optical fiber and easy handling similar to copper cable, is expected to be a high speed network medium. It has been reported that the GI POF enabled gigabit data transmission. Furthermore, it was also confirmed that higher bandwidth than silica base multimode fiber can be achieved by the perfluorinated polymer base GI POF because of the small material dispersion. In this paper, the recent development of the GI POF is described in detail.

GI型POFの現状として、石英系に匹敵する伝送損失の可能性が明らかにされ、また全フッ素化ポリマーにより低材料分散化され高速化が実現していることを紹介。今後として、基礎的な研究を深めることで、さらなる低損失化の実現を見込めることについて述べた。

Recent status of the POF for high-speed data communication and telecommunication is reviewed. The GI POF was proposed for the first time at Keio University, and currently, several methodologies to fabricate GI POF have been proposed. In this paper, we clarified the great advantage of perfluorinated (PF) polymer as the polymer matrix of low-loss and high bandwidth GI POF. It is generally known that the PF polymer can decrease the intrinsic absorption loss compared with PMMA, which is the conventional material for POF. Furthermore, it was found that low material dispersion of the PF polymer is another advantage to obtain the high bandwidth GI POF. It was clarified for the first time that power distribution of the modes formed by the mode dependent attenuation was the dominant factors of the higher bandwidth of the GI POF than theoretically predicted bandwidth, while the effect of the mode coupling was small.

The dopant system GI POF for high temperature stability both in bandwidth and in attenuation is reported for the first time. We confirmed that the Numerical Aperture (NA) of the GI POF strongly influences the temperature stability of the GI POF in the attenuation. It was confirmed in this paper that the attenuation increment was mainly induced by the bending loss, since the GI POF drawn by high tension tended to show its length shrinkage, resulting in irregular bending due to the orientation relaxation of polymer chain. We clarified optimum drawing tension which maintains high mechanical properties and minimize the length shrinkage of the GI POF at high temperature, and the optimum fabrication conditions of the GI POF for high temperature stability both in bandwidth and in attenuation.

We report on the lasing action of the graded-index polymer optical fibers containing dyes, such as Rhodamine B, Rhodamine 6G, Perylene orange and Pyrromethene 567. These dyes have been incorporated into poly(methyl methacrylate-co-2-hydroxyethyl methacrylate). These fibers were transversely pumped at 532 nm with a frequency-doubled Q-switched Nd-YAG laser. Slope efficiency of 24% and output of 1.2 mJ were obtained with a Rhodamine 6G-doped fiber. Lifetime of 200,000 pulses at 10 Hz was achieved with a Rhodamine B-doped fiber.

光と高分子物質の相互作用という視点の下に原子レベルからマクロな不均一構造に至るまで光学ポリマーにおける光作用の基礎原理とその応用につき紹介する。

GI型POFを用いた情報家電インターフェースの国際標準化動向や、PFポリマー系GI型POFのLAN導入実施例など最近のPOFによる高速通信関連技術に関してを紹介した。

PMMA based GI POF containing a ND-chelate have been fabricated. The absorption spectrum of the fiber exhibited several strong bands in the visible and infrared regions. We have observed infrared fluorescence of the ND3+ ion of the fiber at room temperature when it was pumped with an Ar+ -pumped dye laser at 480nm.

It is clarified for the first time that the effect of the mode coupling on the bandwidth characteristics is very small in the GI POF compared with in the SI POF. Although there have been several trials regarding the theoretical prediction of bandwidth characteristics of GI POF, a disagreement between measured and estimated properties was observed. The origin of disagreement has bees generally explained as the mode coupling effect. However, it is clarified in this paper that the effect of differential mode attenuation is the dominant factor of disagreement between measured and predicted bandwidth characteristics, while the effect of the mode coupling is small. In order to clarify the reason why the calculated bandwidth characteristics of the GI POF shows a disagreement with that measured, differential mode delay and differential mode attenuation were investigated. It was found that the highest order mode in the PMMA based GI POF attenuated 17dB compared with the lowest order mode through 100m transmission. By taking into account this differential mode attenuation, an excellent agreement is observed between calculated and measured result of both the bandwidth characteristics and group delay, in which no mode coupling was considered.

High bandwidth PMMA based GI POF with high thermal stability is proposed. No distortion of bandwidth was observed even after more than 10000 hours aging at 85℃ by selecting the large size aromatic dopant which has the stable secondary interaction with PMMA matrix and maintains the high glass transition temperature (Tg) of the core of GI POF. The relationship between the heat-drawing condition from the GI preform to the fiber and the thermal stability in the attenuation was investigated. It was clarified that the length shrinkage of the fiber during the aging at high temperature caused large attenuation increase. On the other hand, the degree of shrinkage could be tightly controlled by changing the heat-drawing tension. It was confirmed that the GI POF drawn with optimized heat-drawing tension had no shrinkage of the fiber during aging at 70℃ and no attenuation increase was observed.

これまで、慶應大学で研究を続けてきたPMMA系GI型POFの低伝送損失特性、広伝送帯域特性（伝搬モード特性）に加えて、高温、高湿下での伝送特性の経時変化が全くないという優れた信頼性について解説した。

分子内に全く水素原子を含まない全フッ素化ポリマーは、屈折率の波長依存性が極めて小さい低材料分散性を有していることから、石英系光ファイバが伝送することの出来ない世界最高速の伝送を可能にするのはポリマー光ファイバであることを紹介した。

A GI POF containing Rhodamine 6G in poly (MMA-co-2-hydroxyl methacrylate) has been fabricated. Lasing behavior of the fiber was observed by pumping with a frequency-doubled Q-switched Nd: yttrium-aluminum-garnet laser. A slope efficiency of 43% and a lifetime of 110000 shots at a repetition rate of 10 Hz have been observed. With 1.5mJ pump energy, output energy of 640µJ was produced.

ポリマー光ファイバー増幅器とポリマー光ファイバーレーザーの構成、作製方法、増幅・発信特性について解説した。

The significant advantages in bandwidth and low material dispersion of perfluorinated (PF) polymer-based GI POF are theoretically and experimentally reported for the first time. It is confirmed that the low attenuation and low material dispersion of the PF polymer enables 1 Gb/s km and 10Gb/s km transmission at 0.85µm and 1.3µm wavelength, respectively. The PF polymer-based GI POF has very low material dispersion, compared with those of the conventional PMMA-based POF and of multimode silica fiber. Since the PF polymer-based GI POF has low attenuation from the visible to near infrared region, not only the 0.65µm wavelength which is in the low attenuation window of the PMMA-based POF, but other wavelength such as 0.85µm or 1.3µm etc. can be adopted for the transmission wavelength. It is clarified in this paper that wavelength dependence of the optimum index profile shape of the PF polymer-based GI POF is very small, compared to that of silica-based multimode fiber. As a result, the PF polymer based GI POF has greater tolerance in index profile variation for higher speed transmission than multimode silica fiber. The impulse response function of the PF polymer-base GI POF was accurately analyzed from the measured refractive index profile using a Wentzel, Kramers, Brillouin (WKB) numerical computation method. By considering all dispersion factors involving the profile dispersion, predicted bandwidth characteristics of the PF polymer-based GI POF agreed well with that experimentally measured.

A lot of research interests are focused on the introduction of optical fiber even in the access network because of the growing demand for accessing Internet with high bit rate. Since inexpensive total system cost is strong]y required for LAN or access network, we have proposed a large-core, low-loss and high-bandwidth graded-index polymer optical fiber (GI POF) as a promising candidate of physical media. In this paper, we describe the recent development of the GI POF in its attenuation and bandwidth achieved by investigating a new polymer material and by theoretical analysis.