研究者詳細 - 石榑　崇明

論文 - 石榑　崇明

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Low-Loss 3-Dimensional Shuffling Grand-Index Polymer Optical Wave-guide for Optical Printed Circuit Boards

Md. Omar Faruk Rasel, Akira Yamauchi, Takaaki Ishigure

IEICE Transactions on Electronics （電子情報通信学会） E101-c （ 7 ） 2018年07月

研究論文（学術雑誌）, 共著, 査読有り

Low-loss 3-dimensional shuffling graded-index polymer optical waveguides for optical printed circuit boards

Rasel O., Yamauchi A., Ishigure T.

IEICE Transactions on Electronics （IEICE Transactions on Electronics） E101C （ 7 ） 509 - 517 2018年07月

ISSN 09168524

© Copyright 2018 The Institute of Electronics, Information and Communication Engineers. This paper introduces a formation method for 3- dimensional 6 ch. ×6 ch. shuffling structures with graded-index (GI) circular core in a multimode polymer optical waveguide for optical printed circuit boards (OPCBs) using a unique photomask-free fabrication technique named the Mosquito method. The interchannel pitch of the fabricated waveguides is 250 μm, where all the channels consist of both horizontal and vertical bending structures and the last 6 channels in parallel cross over the first 6 channels. We also report 3-dimensional S-shaped polymer waveguides. In the S-shaped waveguides, the first and last 6 channels with both horizontal and vertical core bending composing the above 3-dimensional shuffling waveguide are separated, in order to evaluate the effect of over-crossing on the loss. It is experimentally confirmed that there is no excess insertion loss due to the shuffling structure in the 3-D shuffling waveguide. The evaluated crosstalk of the 3-D shuffling waveguide is lower than -30 dB. The 3-D shuffling waveguide proposed in this paper will be a promising component to achieve high bandwidth density wiring for on-board optical interconnects.

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Core position alignment in polymer optical waveguides fabricated using the Mosquito method

Date K., Fukagata K., Ishigure T.

Optics Express （Optics Express） 26 （ 12 ） 15632 - 15641 2018年06月

© 2018 Optical Society of America. We fabricate multimode polymer optical waveguides with circular graded-index (GI) cores which are aligned in parallel at desired positions using the Mosquito method. In the Mosquito method, three-dimensional wiring patterns can be formed with a simple process. However, the core position is likely to deviate from the designed position because of multiple fabrication factors. Hence, in this paper, the dominant parameters to influence on the core height in the cladding are investigated both theoretically and experimentally. In particular, a linear relationship between the core height and the needle-tip height is confirmed with theoretical fluid analysis. Using this relationship, we succeeded in fabricating a waveguide in which the maximum variation of the core height from the designed value is controlled to be less than 10 µm.

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Precise core alignment in fabrication of polymer optical waveguides using the Mosquito method for three-dimensional optical circuits

Date K., Fukagata K., Ishigure T.

Proceedings of SPIE - The International Society for Optical Engineering （Proceedings of SPIE - The International Society for Optical Engineering） 10535 105351Y-1 - 105351Y-8 2018年02月

研究論文（国際会議プロシーディングス）, 共著, ISSN 9781510615557

© 2018 SPIE. Polymer optical waveguides fabricated using the Mosquito method are expected to realize high bandwidth density 3-dimensional (3-D) on-board wiring. In the Mosquito method, the waveguides are fabricated by dispensing a liquid core monomer into a liquid cladding monomer using a microdispenser. Hence, for the on-board applications particularly 3-D wiring, the core position and alignment accuracies are important to couple the waveguides with the other optical components with high efficiency. We already succeeded in fabricating graded-index core multimode polymer optical waveguides with low propagation loss using the Mosquito method. However, the positions of the formed cores tended to deviate from the original design, since both the core and cladding monomers are in the liquid state during the Mosquito process. In this paper, we apply a fluid analysis simulation using a COMSOL Multiphysics® in order to theoretically simulate the influence of several fabrication parameters on the core position. The calculated core height deviation from the designed height is dependent on the needle-Tip height, because the core positions are influenced by the pressure distribution of cladding monomer caused by the monomer flow. Meanwhile, we find that the monomer wetting on the needle outer wall also affects the core height. When the effect of monomer wetting is taken into account, the simulated core heights are different from the results without the effect of monomer wetting and we can theoretically predict the height of the formed core. Finally, we confirm that the core height can be controlled by adjusting the needle-Tip height setting in which the effect of the monomer flow and wetting theoretically calculated is taken into account in the Mosquito method.

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Design and fabrication of restricted mode launching device for high-speed multimode fiber link

Hatai R., Ishigure T.

Proceedings of SPIE - The International Society for Optical Engineering （Proceedings of SPIE - The International Society for Optical Engineering） 10560 105600V-1 - 105600V-7 2018年02月

研究論文（国際会議プロシーディングス）, 共著, ISSN 9781510616059

© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. The IP traffic in datacenter has rapidly increased over the last couple of years because of the wide deployment of cloud computing services. Hence, multimode fiber (MMF) links are already deployed in the rack-to-rack networks particularly in large-scale datacenters to sustain the rapid growth of data traffic. In recent years, the network topology in datacenters shifts from the legacy tree-type to fabric-type: the leaf and spine structure is requiring higher-bandwidth distant product for the MMF links to maintain low latency. However, the modal dispersion has been a large issue to realize high bandwidth links.To address the problem, we focus on the restricted mode launch (RML) approach, by which optical power is coupled to limited numbers of propagating modes in MMFs. Key parameters for the RML are the numerical aperture (NA) and the spot size on the MMF launch end: both of them should be small to reduce the modal dispersion. These are difficult to achieve with small-size launch systems composed of microlenses. Thus, in this paper, a new compact RML device without using microlenses is designed and fabricated: an axially tapered graded-index (GI) core polymer optical waveguide is applied to the RML exciter. Firstly, the launch condition for a 1000-m long OM3 fiber is investigated by calculating the effective modal bandwidth (EMBc). To realize OM4-grade EMBc, we find that the NA and the spot size of the launching beam should be lower than 0.118 and 33.2 μm, respectively. Also, the polymer waveguides are designed to meet the above conditions. The optimum refractive index profile of the tapered core is calculated by solving the Fick's diffusion equation, and then using the beam propagation method (BPM), the spot sizes and NAs from the tapered polymer waveguides are simulated. Finally, we fabricate GI core tapered waveguides using the imprint method.

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Low-loss graded-index polymer crossed optical waveguide with high thermal resistance

Abe K., Oizumi Y., Ishigure T.

Optics Express （Optics Express） 26 （ 8 ） 4512 - 4521 2018年02月

研究論文（学術雑誌）, 共著, 査読有り

© 2018 Optical Society of America. Abstract: In this paper, crossed polymer waveguides with graded-index (GI) square cores are fabricated using the soft-lithography method. We experimentally demonstrate that the fabricated GI-core crossed waveguides exhibit a much lower insertion loss than conventional step index (SI)-core counterparts, which is almost independent of the cross angle. We also show in this paper that the crossed waveguides fabricated applying organic-inorganic hybrid resins show remarkably high thermal resistance compared to the waveguides fabricated utilizing an acrylate resin and a dopant system we previously reported.

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Competitive Evaluation of Planar Embedded Glass and Polymer Waveguides in Data Center Environments

Richard Pitwon,, Kai Wang,Akira Yamauchi, Takaaki Ishigure,Henning Schröder,Marcel Neitz, and Mayank Singh

Applied Science （MDPI） 7 940 2017年09月

研究論文（学術雑誌）, 共著, 査読有り

Optical printed circuit board (OPCB) waveguide materials and fabrication methods have
advanced considerably over the past 15 years, giving rise to two classes of embedded planar graded
index waveguide based on polymer and glass. We consider the performance of these two emerging
waveguide classes in view of the anticipated deployment in data center environments of optical
transceivers based on directly modulated multimode short wavelength VCSELs against those based
on longer wavelength single-mode photonic integrated circuits. We describe the fabrication of graded
index polymer waveguides, using the Mosquito and photo-addressing methods, and graded index
glass waveguides, using ion diffusion on thin glass foils. A comparative characterization was carried
out on the waveguide classes to show a clear reciprocal dependence of the performance of different
waveguide classes on wavelength. Furthermore, the different waveguide types were connected into
an optically disaggregated data switch and storage system to evaluate and validate their suitability
for deployment in future data center environments.

Access to Document (DOI)

Circular core single-mode polymer optical waveguide fabricated using the Mosquito method with low loss at 1310/1550 nm

安原和貴，於豊，石榑崇明

Optics Express （OSA） 25 （ 8 ） 8524 - 8533 2017年03月

研究論文（学術雑誌）, 共著, 査読有り

We fabricate low-loss single-mode (SM) polymer optical waveguides using a
photomask-free simple technique named the Mosquito method. The insertion losses of a 5-cm
long SM polymer waveguide fabricated are 2.52 dB and 4.03 dB at 1310- and 1550-nm
wavelengths, respectively. The coupling loss between a single-mode fiber and the waveguide
is as low as 0.5 dB including the Fresnel reflection. The 0.5-dB misalignment tolerance in the
radial direction is ± 2.0
μ
m at 1550 nm. The Mosquito method is promising for fabricating
SM polymer optical waveguides compatible with silicon photonics chips.

Planar polymer and glass graded index waveguides for data center applications

Richard Pitwon, Akira Yamauchi, Lars Brusberg, Kai Wang, Takaaki Ishigure, Henning Schröder, Marcel Neitz, Alex Worrall I

Proceeding of SPIE 9753 97530I-1 - 97530I-11 2016年03月

研究論文（国際会議プロシーディングス）, 共著

Embedded optical waveguide technology for optical printed circuit boards (OPCBs) has advanced considerably over the
past decade both in terms of materials and achievable waveguide structures. Two distinct classes of planar graded index
multimode waveguide have recently emerged based on polymer and glass materials. We report on the suitability of
graded index polymer waveguides, fabricated using the Mosquito method, and graded index glass waveguides, fabricated
using ion diffusion on thin glass foils, for deployment within future data center environments as part of an optically
disaggregated architecture. To this end, we first characterize the wavelength dependent performance of different
waveguide types to assess their suitability with respect to two dominant emerging multimode transceiver classes based
on directly modulated 850 nm VCSELs and 1310 silicon photonics devices. Furthermore we connect the different
waveguide types into an optically disaggregated data storage system and characterize their performance with respect to
different common high speed data protocols used at the intra and inter rack level including 10 Gb Ethernet and Serial
Attached SCSI.

Low-loss polymer optical waveguides with graded-index perfect circular cores for on-board interconnection

Yuki Saito,Koji Fukagata, and Takaaki Ishigure

Proceeding of SPIE 9750 975005-1 - 975005-6 2016年03月

研究論文（国際会議プロシーディングス）, 共著

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. We already developed the Mosquito method utilizing a microdispenser, as a fabrication technique for GI circular core polymer waveguides. In the Mosquito method, a liquid-state core monomer is dispensed from a syringe needle into a liquid-state cladding monomer while the needle horizontally scans. 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. 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. It is experimentally found that an almost circular core (50-μm diameter with 1.09 vertical to horizontal ratio of diameter) is formed when a curved needle is used. Finally, we successfully demonstrate a 1.73-dB lower loss in a 5-cm long waveguide compared to the one having the core with a dip.

Low-loss light coupling with graded-index core polymer optical waveguides via 45-degree mirrors

森本祥江，石榑崇明

Optics Express （OSA） 24 （ 4 ） 3550 - 3561 2016年02月

研究論文（学術雑誌）, 共著, 査読有り

We experimentally investigate
the optical loss of graded-index
(GI) core polymer optical waveguides with a 45-degree mirror on their one
end fabricated using the photo-addre
ssing method. In addition, we also
theoretically analyze the loss of GI
square-core waveguides with mirrors
using a ray-trace simulation tool. Then, in the waveguide based optical link
including the optical path conversions
via 45-degree mirrors, we show that
GI waveguides realize lower total optical loss than conventional step-index
(SI) core waveguides. The lower loss in the GI waveguide link is attributed
to the tight optical confinement at the co
re center even after reflection at the
mirrors.

Index-profile design for low-loss crossed multimode waveguide for optical printed circuit board

石榑崇明，四反田圭史郎，大泉悠太郎

Optics Express （OSA） 23 （ 17 ） 22262 - 22273 2015年08月

研究論文（学術雑誌）, 共著, 査読有り

We present an index profile design for remarkably low loss
multimode optical crossed waveguide.
In this paper, we theoretically
calculate the light propagation loss in crossed waveguides with step-index
(SI) and graded-index (GI) square co
res utilizing a ray tracing simulation.
In this simulation, we focus on the index exponent values for the GI profile,
which allows low crossing loss even if the number of crossing is as large as
50 or even if the crossing angle is as low as 20°. It is revealed that an index
exponent of 2.0 for the GI core strongly contributes to exhibit 35 times
lower loss (0.072 dB after 50-perpendicula
r crosses) compared to the loss of
the SI-core counterpart (2.58 dB after the same crossings). The GI cores
with a smaller index exponent exhibit better loss in crossed waveguides
with a wide range of crossing angles from 30° to 90°. Furthermore, we
discuss the effect of the refractive i
ndex profile at the intersection on the
optical loss of crossed waveguides.

Fan-in/out polymer optical waveguide for a multicore fiber fabricated using the Mosquito method

石榑崇明,菅沼大輔

Optics Express 23 （ 2 ） 1585 - 1593 2015年01月

研究論文（学術雑誌）, 共著

超高速光通信の実現に向けて，1本の光ファイバ内に複数コアを集積したマルチコアファイバの研究が盛んに行われている．本論文は，この各コアに信号光を入射する/各コアからの信号光を取り出す技術の一つして，ポリマー製のFan-in/out導波路を独自の方法で作製し，その光学特性について明らかにしたものである．作製法として用いたモスキート法は，3次元のコア配線を可能にし，これまでのポリマー光導波路では困難であったFan-in/out構造が得られることを示した．

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

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