研究者詳細 - 石榑　崇明

論文 - 石榑　崇明

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Analysis of interchannel crosstalk in multimode parallel optical waveguides using the beam propagation method

Takuya Kudo and Takaaki Ishigure

Optics Express 22 （ 8 ） 9675 - 9686 2014年04月

研究論文（学術雑誌）, 共著, 査読有り

We theoretically analyze the origin of inter-channel crosstalk in
densely aligned multimode parallel optical waveguides for on-board
interconnects using the Beam Propagation Method. In this paper, we
demonstrate that the inter-channel crosstalk due to mode coupling is very
low in graded-index (GI) circular-core waveguides because the propagation
constants of the propagating modes are discrete. Additionally, it is also
found that the waveguides with GI-type circular cores is sensitive to the
optical confinement in the cladding: low-power cladding modes largely
decrease the mode conversion.

Accurate interchannel pitch control in graded-index circular-core polymer parallel optical waveguide using the Mosquito method

Ryota Kinoshita, Daisuke Suganuma, and Takaaki Ishigure

Optics Express 22 （ 7 ） 8426 - 8437 2014年04月

研究論文（学術雑誌）, 共著, 査読有り

We successfully fabricate polymer optical waveguides with graded-index (GI) circular cores whose diameter and interchannel pitch are accurately controlled using the Mosquito method: GI-core waveguides with 250-, 125- and 62.5-μm pitches are successfully obtained. The Mosquito method utilizing a microdispenser is a very simple technique for fabricating GI-circular-core polymer optical waveguides. The accurately controlled pitch is confirmed by a high connectivity with a commercially available multimode fiber (MMF) ribbon with a 125-μm pitch. Furthermore, by inserting the waveguide between two 12-channel MMF ribbons, we experimentally demonstrate 11.3 Gbps × 12 Ch. parallel signal transmission through a GI-core waveguide with a 125-μm pitch for the first time to the best of our knowledge.

Polymer Optical Waveguides With GI and W-Shaped Cores for High-Bandwidth-Density On-Board Interconnects

木下遼太，守谷公雄，長木　浩司，石榑崇明

Journal of Lightwave Technology （IEEE/OSA） 31 （ 24 ） 4004-4015 2013年12月

研究論文（学術雑誌）, 共著

We fabricate polynorbornene-based graded-index
(GI) core polymer optical waveguides using the photoaddressing method, and demonstrate that the GI-core polymer waveguides are capable of realizing high-bandwidth-density on-board optical interconnects. Because of the tight optical confinement effect of the parabolic refractive index profile, the fabricated GI-core polymer waveguides exhibit superior optical properties compared to stepindex (SI) core polymer waveguides: low propagation loss, low connection loss with GI multimode fiber (MMF) with wide misalignment tolerance, and low interchannel crosstalk even under a small pitch size are experimentally confirmed. Furthermore, interchannel crosstalk due to multicore operation is experimentally evaluated, and a method to estimate the interchannel crosstalk in multimode polymer parallel optical waveguides under multicore
operation is proposed for the first time, to the best of our knowledge. The photoaddressing method capable of fabricating even low-loss GI-core polymer waveguide circuits will pave the way for realizing low-cost and high-bandwidth-density optical printed circuit boards.

Photonic bandgap Bragg fiber sensors for bending/displacement detection

Hang Qu, Tiberius Brastaviceanu, Francois Bergeron, Jonathan Olesik, Ivan Pavlov, Takaaki Ishigure, and Maksim Skorobogatiy

Applied Optics （OSA） 52 （ 25 ） 6344-6349 2013年09月

研究論文（学術雑誌）, 共著, 査読有り

We demonstrate an amplitude-based bending/displacement sensor that uses a plastic photonic bandgap
Bragg fiber with one end coated with a silver layer. The reflection intensity of the Bragg fiber is
characterized in response to different displacements (or bending curvatures). We note that the Bragg
reflector of the fiber acts as an efficient mode stripper for the wavelengths near the edge of the fiber
bandgap, which makes the sensor extremely sensitive to bending or displacements at these wavelengths.
Besides, by comparison of the Bragg fiber sensor to a sensor based on a standard multimode fiber
with similar outer diameter and length, we find that the Bragg fiber sensor is more sensitive to bending
due to the presence of a mode stripper in the form of a multilayer reflector. Experimental results show
that the minimum detection limit of the Bragg fiber sensor can be as small as 3 μm for displacement
sensing.

Analysis of Connection Loss for a GI Waveguide Based Optical Link Using the Finite Difference Beam Propagation Method

徐祥瀚，石榑崇明，中川茂

Journal of Lightwave Technology （IEEE/OSA） 31 （ 12 ） 2036-2042 2013年06月

研究論文（学術雑誌）, 共著, 査読有り

The connection loss which occurs when light transfers
from one medium to another attracts additional attention in highspeed and low-power optical links. In this paper, we not only experimentally apply graded index polymer optical waveguide (GIPOW) in the optical link, but also theoretically address some key parameters which largely influence on the connection loss. The experimental setup of this optical link is composed of a VCSEL module, a GI polymer optical waveguide for the transmitter side(WGTx), a GI multimode fiber (GI-MMF), a GI polymer optical waveguide for the receiver side (WGRx), and a detector. We assume that WGTx is launched by a single mode fiber and then measure the connection losses at the interface between any two components. The results show the connection loss between the GI-MMF and the WGRx is approximately 0.4 dB higher than that of the WGTxto theGI-MMF. For the theoreticalmodeling, we start from the fundamental scalar wave equation, and apply the finite difference beam propagation method (FD-BPM) to simulate the behavior of light inside the waveguide. Furthermore, Fresnel reflection between two media and the scattering effect within polymer optical waveguides are also taken into account. The simulated results show a similar trend to the measured values. Finally, we conclude that the scattering effect could be one of the key issues of GI-POW for maintaining low connection losses with other waveguides
and fibers.

Fabrication of a Graded-Index Circular-Core Polymer Parallel Optical Waveguide Using a Microdispenser for a High-Density Optical Printed Circuit Board

相馬　一友　石榑崇明

IEEE Selected Topics in Quantum Electronics （IEEE） 19 （ 2 ） 3600310 2013年04月

研究論文（学術雑誌）, 共著, 査読有り

A simple fabrication method for multimode polymer optical waveguides with graded-index (GI) circular cores is introduced for use in optical printed circuit boards (O-PCBs). The new method, named “Mosquito method,” utilizes a microdispenser to dispense a viscous monomer directly onto the substrates. By optimizing the dispensing conditions, 12-channel parallel waveguides with circular GI-cores (core diameter of 40 μm) are successfully fabricated using the Mosquito method. The advantages of GI-core waveguides for O-PCB applications are discussed by comparing the optical characteristics of the fabricated waveguides with those of conventional step-index (SI) square-core polymer waveguides, and even with those of silica-based GI multimode fibers (MMFs), as an ideal case. To the best of our knowledge, this is the first comparison of SI- and GI-core multimode polymer waveguides that are composed of the same polymer materials and that have similar core and pitch sizes. We experimentally demonstrate that the GI circular-core polymer waveguides fabricated by the Mosquito method have sufficiently low propagation loss (0.033 dB/cm at 850 nm), low connection loss with GI-MMFs, and low interchannel crosstalk. We observe approximately −50 dB of interchannel crosstalk in the 250-μm pitch GI-core waveguide fabricated, which is almost 10 dB lower than in the SI counterpart. Furthermore, sufficiently low crosstalk is maintained in a half-pitch GI-core waveguide fabricated by the Mosquito method.

Carbon nanotube/polymer composite coated tapered fiber for four wave mixing based wavelength conversion

Bo Xu, Mika Omura, Masato Takiguchi, Amos Martinez, Takaaki Ishigure, Shinji Yamashita, and Takahiro Kuga

Optics Express （OSA） 21 （ 3 ） 3651-3657 2013年02月

研究論文（学術雑誌）, 共著, 査読有り

Brillouin Gain Spectrum Characteriza-tion in Perfluorinated Graded-Index Polymer Optical Fiber with 62.5-μm Core Diameter

水野洋輔，石榑崇明，中村健太郎

IEEE Photon. Technol. Lett., （IEEE） 23 （ 24 ） 1863-1865 2011年11月

研究論文（学術雑誌）, 共著, 査読有り

We characterize the Brillouin gain spectra (BGS) in perfluorinated graded-index polymer optical fibers (PFGI-POFs) with 62.5-μm core diameter. First, we show that the Stokes power is extremely high compared to that of a standard PFGI-POF with 120-μm core, and discuss the Brillouin threshold power. Then, we demonstrate that the PFGI-POF length has little influence on the BGS when the length is longer than 50 m. We also predict that, at 1.55-μm wavelength, it is difficult to reduce the Brillouin threshold power of PFGI-POFs below that of long silica single-mode fibers even if their core diameter is sufficiently reduced to satisfy the single-mode condition. Finally, we confirm the Brillouin linewidth narrowing effect.

Fabrication and inter-channel crosstalk analysis of polymer optical waveguides with W-shaped index profile for high-density optical interconnections

徐祥瀚，廣部佑介，石榑崇明

Optics Express （Optical Society (OSA)） 19 （ 15 ） 14018-14030 2011年07月

研究論文（学術雑誌）, 共著, 査読有り

Observation of stimulated Brillouin scattering in polymer optical fiber with pump-probe technique

水野　洋輔，岸，保立　和夫，石榑崇明，中村　健太郎

Optics Letters （Optical Society （OSA)） 36 （ 12 ） 2378-2380 2011年06月

研究論文（学術雑誌）, 共著

Stimulated Brillouin scattering (SBS) in a perfluorinated graded-index polymer optical fiber (POF) with 120 μm
core diameter was experimentally observed for the first time, to the best of our knowledge, at 1:55 μm wavelength
with the pump–probe technique. Compared to spontaneous Brillouin scattering previously reported, the Brillouin
gain spectrum (BGS) was detected with an extremely high signal-to-noise ratio, even with a short POF (1m) and
scrambled polarization state. We also investigated the BGS dependences on probe power and temperature, which
indicate that SBS in a POF measured with this technique can be utilized to develop high-accuracy temperature
sensing systems.

GI-core polymer parallel optical waveguide with high-loss, carbon-black-doped cladding for extra low inter-channel crosstalk

宇野　久　/　石榑崇明

Optics Express （Optical Society (OSA)） 19 （ 11 ） 10931-10939 2011年05月

研究論文（学術雑誌）, 共著, 査読有り

屈折率分布型コアポリマー並列光導波路に関する学術誌論文である．光導波路のクラッド部に，光吸収性の高いカーボンブラック粒子を添加することにより，屈折率分布型ポリマー光導波路の利点である「低クロストーク特性」をさらに向上できることを実験的に示した論文である．既存の光導波路構造では，コア部の吸収損失が増大してしまうため，本法を用いることはできなかった．

Polymer optical waveguide with multiple graded-index cores for on-board interconnects fabricated using soft-lithography

石榑崇明 / 新田陽介

Optics Express （Optical Society (OSA)） 18 （ 13 ） 14191-14201 2010年06月

研究論文（学術雑誌）, 共著

We successfully fabricate a polymer optical waveguide with
multiple graded-index (GI) cores directly on a substrate utilizing the softlithography method. A UV-curable polymer (TPIR-202) supplied from Tokyo Ohka Kogyo Co., Ltd. is used, and the GI cores are formed during the curing process of the core region, which is similar to the preform process we previously reported. We experimentally confirm that near
parabolic refractive index profiles are formed in the parallel cores (more than 50 channels) with 40 μm x 40 μm size at 250-μm pitch. Although the loss is still as high as 0.1 ~0.3 dB/cm at 850 nm, which is mainly due to scattering loss inherent to the polymer matrix, the scattering loss attributed to the waveguide’s structural irregularity could be sufficiently reduced by a graded refractive index profile. For comparison, we fabricate step-index (SI)-core waveguides with the same materials by means of the same process. Then, we evaluate the inter-channel crosstalk in the SI- and GI-core waveguides under almost the same conditions. It is noteworthy that remarkable crosstalk reduction (5 dB and beyond) is confirmed in the GI core waveguides, since the propagating modes in GI-cores are tightly confined near the core center and less optical power is found near the core-cladding boundary. This significant improvement in the inter-channel
crosstalk allows the GI-core waveguides to be utilized for extra high-density on-board optical interconnections.

High-density channel alignment of graded index core polymer optical waveguide and its crosstalk analysis with ray tracing method

徐祥瀚 / 石榑崇明

Optics Express （Optical Society (OSA)） 18 （ 13 ） 13368-13378 2010年06月

研究論文（学術雑誌）, 共著

We fabricate graded index (GI) multi-channel polymer optical
waveguides comprised of poly methyl methacrylate(PMMA)-poly benzyl methacrylate copolymer for the purpose of achieving high thermal stability
in the GI profiles. The waveguides obtained show slightly higher propagation loss (0.033 dB/cm at 850 nm) than doped PMMA based GI core polymer waveguides we have reported, due to the excess scattering loss inherent to the mixture of copolymer and homo-polymer in the core area. In this paper, we focus on the influence of the excess scattering loss on mode conversion and inter-channel crosstalk. We simulate the behavior of light propagating inside the core with and without the scattering effect.
Using the simulation, the excess loss experimentally observed in the copolymer-core waveguide is successfully reproduced, and then, we find that the excess scattering loss of 0.008 dB/cm could increase the inter channel crosstalk from −30 dB to −23 dB which agrees with the
experimentally observed value. Although the simulation of the inter channel crosstalk was performed only on our GI-core polymer optical waveguides, it is capable of modeling the conventional SI rectangular-core waveguides. Some amount of excess scattering is generally observed in the conventional SI-core waveguides, and thus, the application of this simulation to SI-core waveguides allows a feasible design for high-density alignment of the waveguides.

Carbon Nanotube-Doped Polymer Optical Fiber

内田　翔，マルチネス　アモス，ソン　ヨンドン，石榑崇明，山下真司

Optics Letters （Optical Society (OSA)） 34 （ 20 ） 3077-3079 2009年10月

研究論文（学術雑誌）, 共著, 査読有り

Polymer parallel optical waveguide with graded-index rectangular cores and its dispersion analysis

小杉友哉，石榑崇明

Optics　Express （Optical Society (OSA)） 17 （ 18 ） 15959-15968 2009年08月

研究論文（学術雑誌）, 共著, 査読有り

High-Density 2 X 4 Channel Polymer Optical Waveguide with Graded-Index Circular Cores

武吉　祐佑，石榑崇明

Journal of Lightwave Technology （IEEE/OSA） 27 （ 14 ） 2852-2861 2009年

研究論文（学術雑誌）, 共著, 査読有り

Fabrication of Carbon nanotube poly-methyl-methacrylate composites for nonlinear photonic devices

アモス　マルチネス / 内田翔 / ヨンウォン　ソン / 石榑崇明,　山下真司

Optics Express （Optical Society of America） 16 （ 15 ） 11337-11343 2008年07月

研究論文（学術雑誌）, 共著, 査読有り

Polymer Parallel Waveguide with Circular W-shaped Index Profile Cores

武吉佑祐 / 石榑崇明

IEEE Photonics Technology Letters （IEEE） 19 （ 22 ） 1795-1797 2007年11月

研究論文（学術雑誌）, 共著, 査読有り

Densely Aligned Multichannel Polymer Waveguide With Low Inter-Channel Crosstalk

武吉　佑祐　/　石榑崇明

IEEE Photonics Technology Letters （IEEE） 19 （ 19 ） 1430-1432 2007年10月

研究論文（学術雑誌）, 共著

屈折率分布型円形コアを有するポリマー並列導波路は，従来の均一屈折率コア型導波路に比べて，屈折率分布によりコア部への光の閉じ込め効果が強く，従って，より高密度に並列配線を施しても，チャネル間のクロストークが十分に低減できることを実験的に明らかにした．また，コア部への光の入射位置ずれに対しても許容が大きく，低クロストークを保てることを確認した．

Polymer waveguide with 4-channel graded-index circular cores for parallel optical interconnects

石榑崇明　/ 武吉祐佑

Optics Express （Optical Society of America） 15 （ 9 ） 5843-5850 2007年04月

研究論文（学術雑誌）, 共著, 査読有り

ハイエンドルータやサーバ，HPCなどの筐体内光インターコネクションを実現する低損失で高密度・高速伝送ポリマー並列光導波路を初めて提案した論文である．従来型のポリマー導波路は半導体プロセスによる作製法をベースとしているため，コア部が矩形で均一屈折率コアを有するが，本提案の導波路は，円形で屈折率分布型コアを有する．このため，従来導波路に比べ，十分な低損失性と広帯域性，さらに，強いコア部への光閉じ込め効果を有することを示した．

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