Presentations

In this paper, we theoretically analyze the optical loss in multimode waveguides based optical links including optical path conversion via a 45-degree mirror using a ray-trace simulator. We focus on some waveguide structural parameters: the cladding thickness, the core size, and the refractive index of the core and cladding material, and confirm the optimum waveguide parameters for GI circular-core waveguides for realizing low-loss light coupling. In addition, we experimentally investigate the optical loss of GI circular-core polymer optical waveguides fabricated using the Mosquito method. The fabricated waveguide exhibits low optical insertion loss and low inter-channel crosstalk even after mirror fabrication on its one end.

Using the Mosquito method, we fabricate low-loss multimode polymer optical waveguides with graded-index (GI) perfect circular cores for the applications to on-board optical interconnection. Originally we used siloxane based monomers. In this paper, novel organic-inorganic hybrid materials (SUNCONNECT®) are selected to confirm the applicability of wide-range polymers to the Mosquito method. Here, a dip is observed on the upper perimeter of the obtained core cross-sections particularly when using a straight needle with a wall-thickness of more than 75 m. Such a core-shape deformation increases the coupling loss with circular-core optical fibers. So, the flow of core and cladding monomers while dispensing the core with the needle scan is visually observed. It is confirmed that the edge of the straight needle chips off the upper perimeter of the core when the core monomer is dispensed, leading to the dip. Therefore, the straight needle is replaced for a curved one to change the dispensing direction for eliminating the dip. Finally, we successfully demonstrate a 1.65-dB lower loss in a 5-cm long waveguide compared to the one having the core with a dip.

We have reported a fabrication technique for multimode GI circular-core polymer parallel optical waveguides named the “Mosquito method”, and demonstrated not only straight parallel waveguides but also horizontally and vertically curved designs with excellent optical characteristics. For higher density interconnection, multilayer waveguides are expected. The Mosquito method is capable of fabricating such a multilayer waveguide very easily. However, the core position accuracy is a concern because the liquid state monomer flows due to the needle scan for dispensing the cores. In this paper, we successfully fabricate multilayer GI-circular core polymer parallel optical waveguides by optimizing the needle scan program, and realize a high core-position accuracy with a 125-m horizontal pitch. Then, we measure the optical characteristics of these waveguides and discuss the effect of core position error on the loss.

In this paper, we report on the applications, as SM optical waveguides as well as lens arrays for optical connectors, of our organic-inorganic hybrid material, “SUNCONNECT®”. With respect to waveguide application, fabrication and optical property of GI (graded-index) optical waveguide and SI (step-index) optical waveguide was explained. In addition, lens array for optical coupling was fabricated by using conventional imprint mold.

We theoretically analyze the optical loss in multimode waveguide based optical links including optical path conversion via a 45-degree mirror using a ray-trace simulator. We demonstrate a benefit of GI circular-core waveguides over the conventional SI square-core waveguide.

We present a pitch conversion structure (250 - 125 μm pitch) in multimode polymer optical waveguides for high density interconnects, and investigate how to improve the coupling efficiency with a 12-ch. MMF ribbon.

We fabricate multilayer graded-index circular core multimode polymer parallel optical waveguides using the Mosquito method by optimizing the needle scan program, and realize a high core-position accuracy with a 125-μm vertical and horizontal pitch.

Optical loss of waveguides caused at the connection points with other optical components and the accuracy of the alignment at the connection points are important issues to apply the waveguides for on-board interconnects. In this research, GI-circular-core polymer tapered waveguides are fabricated, in which a taper structure in which the core diameter gradually decreases along with the waveguide axis is formed. The GI circular core tapered polymer waveguides are fabricated using the Mosquito method. The GI cores are formed utilizing the diffusion between the core and cladding monomers. Polymer waveguides with a tapered structure maintaining a circular core cross-section is successfully fabricated. Meanwhile, we discuss the refractive index profile calculated from the diffusion equation: simulated and measured index profiles are compared.

For the application to optical printed circuit boards, we developed the“Mosquito method,”as a fabrication technique for GI circular core polymer optical waveguides utilizing a microdispenser. However, multilayered waveguide using the Mosquito method has high crosstalk to the vertical neighbor cores. In this paper, we suppress this interchannel crosstalk for densely-aligned multilayered polymer optical waveguide.

High performance computing (HPC)のさらなる高性能化を見据え，光インターコネクト技術の導入が期待されており，マルチモードポリマー光導波路を用いた光配線板が検討されている．光配線板では，光源としてVCSEL(垂直面発光レーザ)を用いることが想定されているため，光源-導波路間・導波路-受光器間の結合部に，導波路端に形成した45°ミラーによる直角光路変換が必要とされる．この45°ミラーを介した光結合の際に生じる損失は，光配線板上の導波路ベース光リンクを構成する上で懸念事項となっている．本研究では，45°ミラーを形成した光導波路による，オンボード・ボード間光配線のリンクロスを，光線追跡シミュレーションにより計算し，低リンクロスを実現する光導波路の最適構造を議論する．

我々は，データセンタネットワーク配線の主流であったマルチモードファイバ（MMF）との高い接続性に重きを置いてポリマー光導波路の研究開発をを進めてきた．その中から考案したモスキート法は，マルチモードのみならずシングルモード導波路，さらには，従来のリソグラフィを応用した手法では作製が困難な導波路素子を容易に作製できることが分かってきた．本稿では，これまでに我々が報告してきたポリマー光導波路のオンボード光配線への適合性について紹介する．

ボード上の自由な光配線パターンの実現に向け，交差構造と曲げ構造両方を併せ持つ，シャフリング構造を有する低損失屈折率分布（GI）型ポリマー光導波路の作製を試みた．初めに，S字曲げ光導波路と交差光導波路をそれぞれ単独に作製することで，曲げ損失と交差損失を個々に見積もり，その結果を基にシャフリング構造を最適設計して作製した．得られたGI型シャフリング光導波路は，損失が交差角度に依存しないため，交差角度を低角にすることで，シャフリング構造に要する面積を低減でき，高密度化にも貢献することが明らかになった．更なる高密度配線化を目指し，最密シャフリング光導波路を作製した結果，GI型コアにて交差角度を30oにすることで，シャフリング損失が0.28 dBという非常に低損失な最密シャフリング光導波路の作製に成功した．