論文 - 石榑　崇明

Fabrication of graded-index core polymer optical waveguides enabling low loss with small bend radius (∼1 mm) using high ∆ resins

Karakawa M., Ishigure T.

Optics Express 34 （ 4 ） 6895 - 6907 2026年02月

　概要を見る

In this paper, circular graded-index (GI) core polymer optical waveguides are fabricated using the Mosquito method, applying a combination of resins with a high refractive index difference (∆) for their core and cladding materials. Optical properties of the fabricated waveguides are thoroughly evaluated. These waveguides are expected to exhibit strong optical confinement in their cores due to the synergistic effects of the high ∆ and GI refractive index profile. Notably, the experimentally fabricated multimode polymer optical waveguides achieve a bending loss of less than 0.1 dB, even under extreme conditions involving a 90° bend with a bend radius as small as 1 mm.

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Biogenic design of silicious architectures on Moso bamboo culm

Kazama M., Watanabe H., Hasekura C., Wakabayashi T., Ishigure T., Oaki Y., Imai H.

Scientific Reports 15 （ 1 ）  2025年12月

　概要を見る

Biosilicas that are produced in vascular plants (plant opal), such as Poaceae, have a variety of shapes and functions and are regarded as an excellent model for the architectural design of artificial amorphous materials. In this work, we studied the micro- and nanostructures and mechanical and optical functions of plant opals on the bamboo culm, which is available as an important natural material. The surface of the culm wall is totally covered with silicified epidermal cells containing silica wedges. The biogenic silicious architectures, such as silicified cell walls and wedges, are composed of nanoscale particles ~ 20–80 nm in diameter with cellulose nanofibrils. Silica wedges, which have a relatively low organic content and relatively high hardness and Young’s modulus, are initially formed on cellulose nanofibrils in an organic frame as a scaffold within a few weeks after the emergence of a bamboo shoot. Several months after the formation of the wedges, the epidermal cell walls, which protect the culm surface, are lightly silicified with cellulose nanofibrils. According to a numerical simulation, the silica wedges would have an optical function delivering sunlight to chloroplasts located under the epidermal cells.

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PDMS-based tactile sensing: distributed sensor with a multiple-core polymer waveguide

Yin Y., Ishigure T.

Optics Express 33 （ 20 ） 42573 - 42585 2025年10月

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In this paper, we create a planar polymer optical waveguide sensor with four parallel cores. This four-core array features an optimized geometry obtained through a beam propagation method simulation. UV-curable polydimethyl siloxane is selected for the cladding, while a UV-curable acrylate resin is selected as the waveguide core. When pressure is applied to the core at different locations, precise sensing of the pressure value and location is achieved through changes in the output light intensity from the pressurized cores. The experimental results show that the sensitivities of four cores, Ch.1 to 4, in a fabricated waveguide sensor in a pressure range of 0-1.13 MPa, are 8.7 dB/MPa, 10.73 dB/MPa, 9.2 dB/MPa, and 10.88 dB/MPa, respectively. Additionally, we propose a 3D crossed core structure as a potential direction for future development. Optical waveguide structures not only demonstrate good flexibility and high sensitivity, but also have broad application potential, especially in the fields of flexible electronics and smart sensing.

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Temperature dependence of the coupling loss between polymer optical waveguides and SMF for co-packaging

Kinoshita R., Ishigure T.

Optics Express 33 （ 1 ） 1271 - 1286 2025年01月

　概要を見る

We theoretically calculate the coupling loss between single-mode fibers (SMFs) and polymer optical waveguides with different refractive index profiles. Temperature resistance is one of the concerns when integrating polymer optical waveguides near the electronics and photonics chips where they are highly likely to dissipate heat. Hence, the calculation focuses on the core size variations due to changes in operating temperature. The calculated results show that the refractive index variation with respect to temperature has a greater impact on coupling loss compared to the temperature-dependent core size variation. Then, polymer optical waveguides are experimentally fabricated and characterized. The temperature dependence of the output light intensity distribution from the fabricated waveguides is observed, as it is estimated by the theoretical calculation. In addition, it is also found that graded-index cores in polymer waveguides demonstrate slightly higher temperature stability in connection with SMF than their step-index counterparts. Such a low coupling loss with SMF could be maintained even in an environment at 100 °C, making polymer optical waveguides promising for the application of co-packaged optics.

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Extremely Low Bending Loss (<0.5 dB at 1-mm Bending Radius) GI Core Polymer Optical Waveguide

Karakawa M., Ishigure T.

14th IEEE CPMT Symposium Japan Icsj 2025 Advanced Electronics Packaging Technology for Digital Twin    9 - 12 2025年

　概要を見る

In this paper, we fabricate GI-core single-mode and multimode polymer optical waveguides with remarkably high Δ by applying newly developed resins with high index contrast to the Mosquito Method. The fabricated single-mode waveguides exhibit high optical confinement, achieving a mode field diameter (MFD) of less than 3μ m.

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Core Position Accuracy Improvement of Polymer Optical Waveguide Fabricated Using the Mosquito-Method

Nakao A., Ishigure T.

14th IEEE CPMT Symposium Japan Icsj 2025 Advanced Electronics Packaging Technology for Digital Twin    140 - 141 2025年

　概要を見る

In this paper, we report on the improvement of core dispense position accuracy (both horizontal and vertical) in polymer optical waveguides fabricated using the Mosquito method.

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Application of Graphene-Doped Polymer Optical Waveguides to Wavelength Convertor

Kuboyama K., Yamaguchi N., Set S.Y., Yamashita S., Ishigure T.

14th IEEE CPMT Symposium Japan Icsj 2025 Advanced Electronics Packaging Technology for Digital Twin    100 - 103 2025年

　概要を見る

Polymer optical waveguides with nanocarbondoped cores are fabricated using the Mosquito method, and their wavelength conversion efficiency based on four-wave mixing (FWM) is investigated. Waveguides doped with carbon nanotubes (CNTs), graphene, and graphene oxide (GO) exhibit FWM in all devices. The measured conversion efficiencies are -44.0 dB for CNT, -43.0 dB for graphene, and -46.0 dB for GO, showing improvements compared with the back-to-back configuration of -46.9 dB. Waveguide length dependence is also investigated, confirming the influence of propagation loss and the limited effect of length extension on conversion efficiency. These results demonstrate the potential of nanocarbon-doped polymer waveguides as practical wavelength convertors in photonic networks.

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Low Wavelength Dependent Polymer Waveguide Type Multiplexer for MDM Link

Kanai T., Ishigure T.

14th IEEE CPMT Symposium Japan Icsj 2025 Advanced Electronics Packaging Technology for Digital Twin    104 - 107 2025年

　概要を見る

To expand optical fiber transmission capacity by combining mode division multiplexing (MDM) and wavelength division multiplexing (WDM), we reduce the wavelength dependence in the insertion loss of waveguide-type MUX/DEMUX devices expected to be applied to MDM. This is achieved by introducing an axial tapered core into the device.

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Steeply Bent Core Single-Mode Polymer Waveguide with Low Bending Loss Fabricated Using the Mosquito Method

Tanimoto A., Ishigure T.

14th IEEE CPMT Symposium Japan Icsj 2025 Advanced Electronics Packaging Technology for Digital Twin    142 - 143 2025年

　概要を見る

Steeply bent core single-mode polymer optical waveguides are fabricated by varying the bending radius and core diameter using the Mosquito method. Then, we confirm that the small bending radius contributes to satisfy the singlemode condition even when the waveguide has high Δ. The bending loss under 1-mm bending radius can be reduced by designing slightly larger core size as 8.0 μ m.

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Quantum Dot Doped Polymer Optical Waveguide Amplifier

Kitta H., Ishigure T.

14th IEEE CPMT Symposium Japan Icsj 2025 Advanced Electronics Packaging Technology for Digital Twin    138 - 139 2025年

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In this paper, we fabricate polymer optical waveguides doped with CdSe/ZnS quantum dots by applying the Mosquito method. The dependence of insertion loss and fluorescence intensity on the doping concentration is evaluated, and the potential application of these waveguides to optical amplifier devices is investigated.

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Polymer Waveguide-Based Optical Tactile Sensor Fabricated by the Mosquito Method

Yin Y., Ishigure T.

IEEE Sensors Journal 25 （ 18 ） 34636 - 34645 2025年

ISSN  1530437X

　概要を見る

In this article, optical waveguides are designed for ultrasensitive tactile sensing with fast response and high sensitivity. We create a polymer-based optical waveguide sensor that has been innovatively developed to address the limitations of conventional optical fiber-based sensors, particularly their flexibility and tactile capabilities. The principle of the sensor is output light intensity variation due to core bending. Our optical waveguides consist of polydimethylsiloxane (PDMS) as the cladding. An acrylate resin (XCL-02) is used for the core by dispensing its monomer into the PDMS (cladding) monomer using the Mosquito method. We demonstrate that there is a nearly linear relationship between the extra pressure and the insertion loss of the waveguide. The PDMS-based sensor exhibits high repeatability in the measurement pressure range. The sensor shows a sensitivity of 9.12 dB/MPa and a measurement range of 0–2.3 MPa, with a core diameter of approximately 100 &mu;m and a light wavelength of 850 nm. This investigation sheds light on crucial factors influencing the sensor’s performance and response to the applied forces. We believe that this sensor can be applied in various fields, such as medical applications, wearable devices, and robotic tactile systems.

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Polymer Optical Waveguide for Display Applications

Ishigure T.

Springer Proceedings in Physics 429 SPPHY   29 - 30 2025年

ISSN  09308989

　概要を見る

We present a unique polymer optical waveguide with circular cores fabricated by our proprietary technology, the Mosquito method. We demonstrate how to form 3D wiring patterns with perpendicularly bent cores with very small bending radii. We discuss the operability of polymer waveguides in the visible wavelength range for display applications.

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Polymer Composite Based No-Core Fiber Structure as Refractive Index Sensor

Saris N.N.H., Razali N.M., Fukui T., Ishigure T., Othman M., Hamzah A., Daud N.A.

Materials Science Forum 1153   77 - 82 2025年

ISSN  02555476

　概要を見る

This study theoretically proposes a refractive index (RI) sensor based on a polymer composite with a no-core fiber (NCF) design structure. Sensor designs with diameter variations of 125 urn, 105 urn, and 85 urn are simulated using the Wave Optics Module of COMSOL Multiphysics® software. The sensors are characterized within an analyte range of 1.470 RIU to 1.500 RIU, at intervals of 0.005 RIU. The results demonstrate effective interaction between the structure and the sensing medium. The highest recorded sensitivity is 4>10~6 (dimensionless) for the 85 um sensor, followed by 2><10~6 for the 105 um sensor, and 1>10~6 for the 125 um sensor. This study offers valuable insights, guiding the optimal design of polymer-based RI sensors for future environmental monitoring, chemistry, and biomedicine applications.

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Miniaturization of 1 × 2 1 × 4 Branched Multimode Polymer Optical Waveguide for MUX Device in SWDM Links

Atsumi K., Ishigure T.

14th IEEE CPMT Symposium Japan Icsj 2025 Advanced Electronics Packaging Technology for Digital Twin    108 - 111 2025年

　概要を見る

Subminiature 1×2 branched multimode polymer optical waveguides with circular GI cores are fabricated using the Mosquito method for application as MUX devices in SWDM links. Then, we evaluate their performance, including the insertion loss dependence on the launch condition. For further dense integration of devices, subminiature 2D 1×4 branched and 3D 1×4 branched waveguides are successfully fabricated.

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Optimum core structural design of the polymer optical waveguides as edge couplers for co-packaging

Kinoshita R., Ishigure T.

Optics Express 32 （ 14 ） 24415 - 24431 2024年07月

　概要を見る

We simulate the optical properties of polymer optical waveguides with different refractive index profiles in their cores as coupling components (edge couplers) between single-mode fiber and SiOx waveguides. In this paper, we focus on the single-mode operation of graded-index (GI) core polymer waveguides, for which we previously demonstrated low propagation loss under multimode operation. We design the optimum core structure (size and index contrast) for different refractive index profiles, and then demonstrate the unique optical properties of GI waveguides contributing to the low optical loss compared to the step-index counterparts, in particular, mode field diameter variation and taper angle tolerance.

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Polarization manipulation on step-index composite polymer beam splitters for photonics circuitry

Afsary N., Tasnim F., Rasel M.O.F., Ishigure T.

Heliyon 10 （ 3 ）  2024年02月

ISSN  24058440

　概要を見る

This paper presents composite beam splitters realized with polymer materials for developing photonic integrated circuits. We used organic-inorganic hybrid polymer materials to form this composite beam splitter realized with step-index (SI) core profiles. We used the alternating direction implicit technique of the Rsoft CAD BeamPROP solver to design and analyze these beam splitters. We successfully examined and manipulated the beam splitter's polarization dependency to obtain a 99% output efficiency with a 50:50 splitting ratio. The SI beam splitter exhibits an excess loss of 0.014 dB. When we apply polarized light in this beam splitter, the excess loss increases to 2 dB, and this loss gradually decreases as the angle of incident light increases. The excess loss reduces to 0.05 dB at the 31-degree angles of the incident polarized light. We also investigated the crosstalk of this beam splitter by varying the wavelength, and it is evident that the lowest crosstalk is −19.77 dB at the polarized angle of 31°.

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3D Polymer Optical Waveguide-based Fan-in/out Device for Silicon Photonics Chips

Ito A., Ishigure T.

British and Irish Conference on Optics and Photonics, BICOP 2024 in Proceedings British and Irish Conference on Optics and Photonics 2024 2024年

　概要を見る

To achieve a subminiature low-loss adiabatic coupler to silicon photonics chips, we design a PMT connector-integrated polymer waveguide device with circular single-mode cores to fabricate it using the Mosquito method.

3D Polymer Optical Waveguide-based Fan-in/out Device for Silicon Photonics Chips

Ito A., Ishigure T.

13th IEEE CPMT Symposium Japan: Innovation of Packaging Technology for Advanced Heterogeneous Integration, ICSJ 2024    162 - 163 2024年

　概要を見る

To realize a subminiature low-loss adiabatic coupler to silicon photonics chips, we design a PMT connector- integrated polymer waveguide device with circular single- mode cores to fabricate it using the Mosquito method.

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Thermally reliable compact electro-optic modulators with a low half-wave voltage

Afsary N., Alam M.K., Rasel M.O.F., Ishigure T.

Optics Continuum 3 （ 6 ） 1012 - 1024 2024年

　概要を見る

Recent advancements in thin-film lithium niobate have led to the development of high-performance integrated electro-optic modulators, which are crucial for modern optical communication systems. These modulators offer tighter mode confinement, a smaller physical footprint, and reduced modulating voltages. This study presents a Mach-Zehnder modulator (MZM) on a silicon nitride-loaded lithium niobate platform using a few-mode waveguide structure. By harnessing the exceptional thermo-optic and electro-optic effects of LiNbO3, we design and simulate this modulator employing multilayer structures with the BeamPROP solver. The modulator has a length of 3.94 mm, a Vπ value of 0.96 V, and a transition temperature (Tg) of 80 °C at 1.55 µm. This proposed modulator exhibits a crosstalk of approximately-42 dB, an extinction ratio of approximately 24 dB, and a maximum transmission of-28 dB for the first-order phase shift. These findings demonstrate the significant potential of this modulator for deployment in high-speed optical communication systems, where maintaining thermal stability and optimizing energy efficiency are paramount.

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Structural Investigation of Microchannel and Optical Waveguide Co-integrated Sensor Devices

Ichizuka T., Ishigure T.

13th IEEE CPMT Symposium Japan: Innovation of Packaging Technology for Advanced Heterogeneous Integration, ICSJ 2024    156 - 157 2024年

　概要を見る

In this paper, we design a device that integrates a microchannel and optical waveguide core, and fabricate it using the Mosquito method. Then, the light output is detected from the core after transmitting through the microchannel.

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