Details of a Researcher - Ishigure, Takaaki

Papers - Ishigure, Takaaki

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Fabrication for Y-branched multimode polymer optical waveguides using the Mosquito method

Nakayama T., Ishigure T.

2018 IEEE CPMT Symposium Japan, ICSJ 2018 (2018 IEEE CPMT Symposium Japan, ICSJ 2018) 155 - 158 2019.01

ISSN 9781538654422

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Graded-index polymer optical waveguide for restricted mode launch device enabling high-bandwidth, longer-reach multimode fiber link

Hatai R., Ishigure T.

2018 IEEE CPMT Symposium Japan, ICSJ 2018 (2018 IEEE CPMT Symposium Japan, ICSJ 2018) 71 - 74 2019.01

ISSN 9781538654422

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Directly inscribed multimode polymer waveguide and 3D device for high-speed and high-density optical interconnects

Xu X., Ma L., Shi Y., Ishigure T., He Z.

Optics Express (Optics Express) 27 ( 16 ) 22419 - 22428 2019

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement A 75-cm-long circular-core polymer waveguide compatible with standard 50-µm-core multimode fibers (MMFs) is designed and fabricated by using a direct inscribing method for high-speed and high-density optical interconnects. The fabricated waveguide has low loss (<0.044 dB/cm at 850 nm) and low crosstalk (<-34 dB with a core pitch of 62.5 µm) with a negligible coupling loss with the MMFs. It also exhibits a low bending loss (<0.08 dB/mm with a bending radius of 4 mm), which agrees well with calculated results. Error-free NRZ data transmission over the 75-cm-long waveguide at 25 Gb/s is demonstrated, and 4 × 25 Gb/s short wavelength division multiplexing (SWDM) is realized on a straight waveguide. Moreover, a two-layer waveguide and a 3-dimensional (3D) Y-splitter/combiner are also fabricated for 3D integration.

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Circular core single-mode 3-dimensional crossover polymer waveguides fabricated with the Mosquito method

Rasel O., Ishigure T.

Optics Express (Optics Express) 27 ( 22 ) 32465 - 32479 2019

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement We experimentally fabricate circular core 3-dimensional (3D) crossover single-mode polymer optical waveguides using a photomask free unique fabrication technique named the Mosquito method for realizing channel shuffling. The 3D crossover structure is accomplished by forming four cores (2 ch. × 2 ch.) with different heights: the last two channels cross over the first two channels with horizontal and vertical core bending. We compare the insertion losses between the fabricated 3D single-mode crossover waveguide and 3D S-bend core waveguides fabricated separately, which correspond to the lower and upper channels in the crossover waveguide. Then, we investigate the effect of the core crossover on the loss, and find that almost negligible additional loss is observed. The average insertion losses of this 6-cm long 3D crossover single-mode waveguide are 3.95 and 3.81 dB at 1310 nm, and 5.74 and 4.80 dB at 1550-nm wavelength, for the lower and upper channels, respectively. The interchannel crosstalk in this crossover waveguide is observed to be lower than −40 dB, while the 1 dB radial alignment tolerance is ± 1.7 and ± 2.1 µm at 1310 and 1550 nm, respectively. These results suggest that the fabricated circular core single-mode 3D crossover polymer waveguides could have a great impact for high-bandwidth-density on-board and inter-chip optical interconnect applications.

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Design and Fabrication of Broadband Polymer Mode (De)Multiplexer Using a Direct Inscribing Method

Xu X., Ma L., Marushima C., Ishigure T., He Z.

IEEE Photonics Journal (IEEE Photonics Journal) 10 ( 6 ) 2018.12

© 2009-2012 IEEE. We demonstrate the design and fabrication of a mode (de)multiplexer based on the tapered mode-selective coupler. The proposed device is directly inscribed in the substrate material by a needle-type liquid micro-dispenser and a three-axis robot stage using commercially available UV-curable resins. The fabricated mode (de)multiplexer has an excess loss less than 0.3 dB, a coupling ratio higher than 0.93, and an extinction ratio higher than 23 dB within a broadband of 100 nm around 1550 nm. The near field patterns of LP{11} mode at different wavelengths were successfully observed using an infrared charge-coupled-device camera. The fabrication tolerance on the spacing, core diameter deviation, and core circularity were investigated and the results imply that our fabrication process can satisfy the requirements on it. The proposed method is capable of fabricating functional devices for high-speed on-board optical interconnects.

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Direct Fabrication for Polymer Optical Waveguide in PMT Ferrule Using the Mosquito Method

Ishigure T., Masuda H., Date K., Marushima C., Enomoto T.

Proceedings - Electronic Components and Technology Conference (Proceedings - Electronic Components and Technology Conference) 2018-May 1103 - 1108 2018.08

ISSN 9781538649985

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Accurate core alignment for polymer optical waveguide in the mosquito method for high-efficient coupling

Morimoto Y., Date K., Ishigure T.

Proceedings - Electronic Components and Technology Conference (Proceedings - Electronic Components and Technology Conference) 2018-May 2444 - 2449 2018.08

ISSN 9781538649985

© 2018 IEEE. We demonstrate the importance of vertical position accuracy of formed core in the polymer optical waveguides fabricated using the Mosquito method for 3-dimensional wiring. We theoretically confirm the core vertical position deviation from the designed position is caused by the several fabrication parameters, the needle size and the needle-scanning speed. As an example of 3-dimensional wiring, we focus on the optical path conversion by 45-degree mirrors, and experimentally investigate the influence of the core vertical position on the coupling efficiency to other components via a 45-degree mirror. By forming the cores on appropriate height in the cladding, graded-index core optical waveguides exhibit a slight loss increment as low as 0.2 dB due to mirror structure, realizing the high efficient coupling via a 45-degree mirror.

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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 ) 2018.07

Research paper (scientific journal), Joint Work, Accepted

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 2018.07

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 2018.06

© 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

Kumi Date, Koji, Fukagata, and Takaaki Ishigure

Proceeding of SPIE (Proceedings of SPIE - The International Society for Optical Engineering) 10535 105351Y-1 - 105351Y-8 2018.02

Research paper (international conference proceedings), Joint Work, ISSN 9781510615557

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

Ryosuke Hatai, Takaaki Ishigure

Proceeding of SPIE (Proceedings of SPIE - The International Society for Optical Engineering) 10560 105600V-1 - 105600V-7 2018.02

Research paper (international conference proceedings), Joint Work, ISSN 9781510616059

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 m, 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

Kohei Abe, Yutaro Oizumi, and Takaaki Ishigure

Optics Express (OSA) 26 ( 8 ) 4512 - 4521 2018.02

Research paper (scientific journal), Joint Work, Accepted

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 resist
ance 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 2017.09

Research paper (scientific journal), Joint Work, Accepted

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.

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

Kazuki Yasuhara, Feng Yu, and Takaaki Ishigure

Optics Express (OSA) 25 ( 8 ) 8524 - 8533 2017.03

Research paper (scientific journal), Joint Work, Accepted

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 2016.03

Research paper (international conference proceedings), Joint Work

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 2016.03

Research paper (international conference proceedings), Joint Work

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

Yoshie Morimoto and Takaaki Ishigure

Optics Express (OSA) 24 ( 4 ) 3550 - 3561 2016.02

Research paper (scientific journal), Joint Work, Accepted

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

Takaaki Ishigure, Keishiro Shitanda, and Yutaro Oizmi

Optics Express (OSA) 23 ( 17 ) 22262 - 22273 2015.08

Research paper (scientific journal), Joint Work, Accepted

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

ISHIGURE TAKAAKI,SUGNUMA DAISUKE

Optics Express 23 ( 2 ) 1585 - 1593 2015.01

Research paper (scientific journal), Joint Work

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．

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