研究者詳細 - 石榑　崇明

論文 - 石榑　崇明

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Formation of 3D Polymer Optical Waveguides

Yakabe S., Manabe K., Sasaki D., Ishigure T.

SEI Technical Review （ 95 ） 5 - 10 2022年10月

ISSN 13434349

The Mosquito method, a polymer optical waveguide fabrication method invented by Professor Ishigure at Keio University, enables the three-dimensional (3D) formation of core patterns in cladding using a commercially available micro dispenser and a multi-axis syringe-scanning robot. This fabrication method is expected to be used to realize devices required for 3D waveguides such as Fan-in/Fan-out (FIFO) devices, which are essential for the introduction of multicore fibers (MCF). On the other hand, prior studies have mainly examined multimode waveguides, and several issues need to be solved for making single-mode devices. In particular, the core shape tends to deteriorate from circular due to monomer flow caused by needle scanning in the cladding, which is a factor that increases the connection loss with the optical fiber. This paper presents a theoretical and experimental study on the fabrication of single-mode waveguides by the Mosquito method and the formation of circular cores using the method to reduce connection loss with single-mode optical fibers.

Fabrication of Y-Branched GI Core Polymer Waveguide and its Application to CWDM MUX Device for Multimode Fiber

Hatai R., Nakazaki F., Nakayama T., Ishigure T.

Journal of Lightwave Technology 40 （ 9 ） 2915 - 2925 2022年05月

ISSN 07338724

This paper describes the characteristics of graded-index (GI) core Y-branched polymer optical waveguides as optical couplers for multimode fibers (MMFs) in coarse wavelength division multiplexing links with a restricted mode launch function. In this paper, we compare two GI-core Y-branched waveguides fabricated using different methods: the Mosquito method and the imprint method. Error free transmission is confirmed when transmitting a 25.6125-Gbps NRZ optical signal (PRBS31) at 850-nm wavelength through a 100-m long OM3 fiber using the waveguide as an optical coupler. We also discuss the function of a restricted mode launch exciter for a 1-km long MMF. From the effective modal bandwidth analysis, realizing higher bandwidth-distance product in long MMFs should be possible by reducing the core size of the waveguide coupler.

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90°-bent graded-index core polymer waveguide for a high-bandwidth-density VCSEL-based optical engine

Kohmu N., Ishii M., Hatai R., Ishigure T.

Optics Express 30 （ 3 ） 4351 - 4364 2022年01月

In this paper, we present a low-loss optical assembly utilizing a 90°-bent graded-index (GI) core polymer optical waveguide on vertical cavity surface emitting laser (VCSEL) based optical transceivers. The proposed assembly can replace conventional components such as mirrors and lenses for realizing subminiature optical engines applicable to on-board integration. To minimize the total insertion loss of the waveguide when connected to a high-speed VCSEL and a GI-core multimode fiber (MMF) at each end, the characteristics of the beam emitted from VCSELs are measured and taken into consideration for the waveguide design. In order to confirm the effect of insertion loss reduction by the waveguide numerical aperture control, 90°-bent GI-core polymer waveguides are fabricated applying the Mosquito method. The fabricated waveguide exhibits a total insertion loss as low as about 2 dB at 850-nm wavelength, which includes the coupling losses at both ends, bending, and propagation losses. We also investigate a way to reduce the insertion loss when a gap exists between the waveguide and VCSEL chip. We theoretically and experimentally confirm that filling the gap with a high index resin can reduce the coupling loss by 5 dB.

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Fabrication for single/few-mode Y-branch waveguide using the Mosquito method

Hatai R., Hama H., Ishigure T.

Optics Express 30 （ 3 ） 3524 - 3537 2022年01月

In this paper, Y-branched circular core single-mode/few-mode polymer optical waveguides are designed and fabricated using the Mosquito method we have developed. They comprise a low loss multiplexing (MUX) device for mode division multiplexing. In the Mosquito method, since a liquid core monomer is dispensed into another liquid cladding monomer while the needle scans along the path of the wiring patterns, it was difficult to form in-plane core crossings and core branches. In this paper, to form single-mode/few-mode Y-branched cores, we apply a unicursal needle-scan path for the Y-branch structure with the Mosquito method. For MUX device applications, cores satisfying the single-mode condition are successfully formed on the two-port side while the one-port side has a few-mode core.

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High-Density Electrical and Optical Assembly for Subminiature VCSEL-Based Optical Engine

Kohmu N., Ishii M., Ishigure T.

IEEE Transactions on Components, Packaging and Manufacturing Technology 12 （ 1 ） 27 - 36 2022年01月

ISSN 21563950

In this article, we propose a subminiature (10.9 mm $\times56.6$ mm) vertical cavity surface-emitting laser (VCSEL)-based optical engine with a low crosstalk penalty for onboard applications. When applying optical engines to onboard interconnects, ICs [laser drivers and transimpedance amplifiers (TIAs)] and active optical devices (light sources and photodetectors) must be mounted densely to make the footprint as small as possible. It is a concern that such a high-density integration could increase the crosstalk between transmitter (Tx) and receiver (Rx) devices, which could be caused by the supply current difference between the circuit from laser drivers to light source and the circuit from photodetectors to TIAs. In this article, by inserting a gap in the ground electrode, a compact optical engine (less than half of the footprint of quad small form-factor pluggable-double density (QSFP-DD) compliant engines) enabling a 25.78-Gb/s error-free optical transmission is successfully fabricated. We optimize the gap width to decrease the crosstalk while maintaining efficient heat dissipation via the electrode. We compare the characteristics of the fabricated optical engine to the engine with the gap-less ground electrode structure formed in the same compact size. Then, we both theoretically and experimentally confirm a link power budget savings of about 1.8 dB, which is sustained even under high-temperature ( $T_{c} = 70\,\,^{\circ }\text{C}$ ) operation. In addition, to realize further high-density assembly, we also represent a lens-less optical coupling by inserting a 90o-bent graded-index (GI) core polymer waveguide between the optical transmitter and multimode fiber. The transmission performance of the 90o-bent GI-core waveguide is preliminarily evaluated, and we successfully transmit 53.125-Gb/s PAM4 optical signals experimentally.

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90-degree bent core polymer optical waveguide coupler for low loss lens-less light coupling between laser / photodetector and fiber

Suemori D., Ishii M., Kohmu N., Ishigure T.

Proceedings - Electronic Components and Technology Conference 2022-May 436 - 440 2022年

ISSN 05695503

In this paper, we present direct fabrication of vertically 90-degree bent core polymer optical waveguide couplers to be integrated in optical engines enabling lens-less light coupling between laser source / photodetector and fiber with low loss. We apply the Mosquito method that we developed as a fabrication technique for single-mode and multimode polymer optical waveguides with circular cores. Because of the unique fabrication procedures of the Mosquito method, three-dimensional core alignment is possible, and thus 90° bent core can be formed directly on a laser chip. We would like to emphasize that the bending radius as small as 2 mm or less could be formed, while the insertion loss of the waveguide is as low as 5 dB.

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Single-mode polymer waveguide for fan-in/fan-out of multicore fiber by the mosquito method

Yakabe S., Ishigure T.

Proceedings of SPIE - The International Society for Optical Engineering 12007 2022年

ISSN 0277786X

In this paper, in order to apply to optical connection components such as fan-in-fan-out (FIFO) devices for multicore fibers (MCFs), we design polymer optical waveguides with circular cores satisfying the single-mode condition, which are fabricated using the Mosquito method, and experimentally demonstrate that the optimum S-shape bent core waveguide can be fabricated as designed. The Mosquito method is a technique we have developed to form circular cores in both multimode and single-mode waveguides using a commercially available microdispenser and multi-axis syringe scanning robot. We have demonstrated that single-mode waveguides fabricated by the Mosquito method can be coupled with SMF with low loss. However, in order to realize a waveguide type FIFO device for MCFs by the Mosquito method, it is necessary to maintain micron-order positioning accuracy for the cores while three dimensionally aligning multiple cores in FIFO patterns. Since the pitch between the cores on the MCF side is very narrow, the core position is likely to deviate from the design value due to the liquid monomer flow caused by needle scan. We statistically confirm the possible amount of deviation from the design position by needle scan and feed it back to the program of needle scan path for the FIFO. We successfully fabricate a four-core FIFO with a desired core pitch. It is experimentally confirmed that the insertion loss is 1.4 dB on average. From these investigations, we confirm that the Mosquito method has an ability to fabricate small and low-loss FIFO devices.

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Investigation of fabrication conditions for Y-branched polymer optical waveguides using the Mosquito method

Sekitani K., Hatai R., Ishigure T.

2022 IEEE CPMT Symposium Japan, ICSJ 2022 100 - 101 2022年

In this paper, the conditions for fabricating Y-branched optical waveguides using the Mosquito method are discussed, focusing on the viscosity of the monomer and the branch angle. With increasing the viscosity of core monomer, the Y-branching structures tend to be distorted particularly when the branching angle is larger than 0.5 degree. After finding out the appropriate fabrication conditions, Y-branched optical waveguides in which two-port cores are vertically stacked are fabricated, taking the advantage of the Mosquito method: the ability to form three-dimensional core wiring patterns. Single-mode and multimode cores are successfully formed in which we could confirm the light propagation.

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GI-core Multimode and Single-mode Polymer Waveguides for High-density Co-packaging

Ishigure T.

2022 Optical Fiber Communications Conference and Exhibition, OFC 2022 - Proceedings 2022年

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GI-core Multimode and Single-mode Polymer Waveguides for High-density Co-packaging

Ishigure T.

Optics InfoBase Conference Papers 2022年

Fabrication for Y-branched Polymer Optical Waveguide Using the Imprint Method and Its Application for Mode Division Multiplexing Devices

Ono S., Ishigure T.

2022 IEEE CPMT Symposium Japan, ICSJ 2022 45 - 48 2022年

We propose an asymmetric polymer Y-branched waveguide for a multiplexer of TE01 and TE11 modes to a few-mode fiber in mode division multiplexing links, in this paper. Fabricated waveguides have square cross-sectional graded-index (GI) cores which exhibit strong optical confinement to the core center. Theoretical loss calculation by BPM shows that the GI core exhibits higher mode splitting ratio and about 1 dB lower insertion loss than the conventional SI core. The measurement results of the fabricated waveguide elucidate that the GI core shows an insertion loss about 1.5 dB lower than the SI core, showing a more pronounced low loss advantage. We also demonstrate in this paper that a square approximation for the core cross-section allows to reduce the coupling loss with fibers and realize a low-loss mode multiplexer, compared to the rectangular cross-sectional core.

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Fabrication for Polymer Optical Waveguide and Its Application for Co-Packaged Optics

Ishigure T.

Journal of Japan Institute of Electronics Packaging 25 （ 2 ） 157 - 161 2022年

ISSN 13439677

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Fabrication for low-loss polymer optical waveguide with vertically 90° bent core

Suemori D., Ishii M., Kohm N., Ishigure T.

2022 IEEE CPMT Symposium Japan, ICSJ 2022 92 - 93 2022年

In this paper, we directly fabricate vertically 90-degree bent core polymer optical waveguide right above a VCSEL chip to be applied to an optical coupler in subminiature on-board optical engine. We have proposed the Mosquito method for fabricating polymer optical waveguide utilizing a microdispenser. In the procedure of the Mosquito method, the vertically 90-degree bent cores are dispensed just above VCSEL chips by taking the advantage of the Mosquito method: ability to form three-dimensional core wiring pattern. We emphasize in this paper that the number of the vertically bent core is increased to three that are aligned in parallel and small bending radius with the 3 parallel core structure can be formed.

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Fabrication for Circular Cross-Sectional Microchannels and Their Application for On-off Valves

Uehara K., Hori Y., Ishigure T.

2022 IEEE CPMT Symposium Japan, ICSJ 2022 119 - 122 2022年

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Design and Fabrication of Three-dimensional Polymer Optical Waveguide-based Fan-in/out Device for Multicore Fibers

Yamaguchi Y., Yakabe S., Ishigure T.

2022 European Conference on Optical Communication, ECOC 2022 2022年

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Design and Fabrication of Three-dimensional Polymer Optical Waveguide-based Fan-in/out Device for Multicore Fibers

Yamaguchi Y., Yakabe S., Ishigure T.

2022 IEEE CPMT Symposium Japan, ICSJ 2022 41 - 44 2022年

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Waveguide length and pump power effects on the amplification of europium aluminum doped polymer

Saris N.N.H., Yoshida Y., Horie T., Hamzah A., Ambran S., Mikami O., Ishigure T., Fukui T.

Optik 239 2021年08月

ISSN 00304026

Mosquito method is used to fabricate a 50 μm core diameter graded index (GI) multimode Eu-Al doped polymer composite optical waveguide amplifier. In this paper, waveguide length and pump power are varied with an input signal of - 30 dB m. Under a 532 nm laser excitation, 16.27 dB optical gain under an optimal 10 cm waveguide length is observed from forward pumping amplification for a threshold pump power of 23 dB m. Also, the waveguide has been characterized to be 0.83 dB/cm at 617 nm wavelength.

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Mosquito method based polymer tapered waveguide as a spot size converter

Kobayashi Y., Sakaguchi Y., Yasuhara K., Ishigure T.

Optics Express （Optics Express） 29 （ 6 ） 9513 - 9531 2021年03月

We create a compact low-loss spot-size converter (SSC) which utilizes a tapered core polymer optical waveguide with circular cross-sectional graded-index (GI) core using the Mosquito method we developed. First, we theoretically analyze the mutual diffusion between the core and cladding monomers, which is a feature unique to the Mosquito method when forming GI cores. The monomer diffusion effect depends on the initial core diameter that is dispensed by a microdispenser and the diffusion time before UV curing: in a small core the monomer diffuses more rapidly than in a large core. Using this diffusion dependence on the initially dispensed core diameter, it is theoretically found that a tapered polymer waveguide based SSC can adiabatically convert the mode-field diameter between 4.0 and 8.6 µm at a 1550-nm wavelength waveguide as short as 4 mm. Next, the tapered waveguide based SSC with the designed structure is experimentally fabricated using the Mosquito method, and we confirm an 8-mm long tapered waveguide with an insertion loss of 1.83dB functions as a SSC that converts the MFD from 4.7 µm to 7.5 µm at 1550-nm wavelength.

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Low loss single-mode polymer optical waveguide with circular cores

Yakabe S., Kobayashi Y., Matsui H., Saito Y., Manabe K., Ishigure T.

OSA Continuum （OSA Continuum） 4 （ 3 ） 1070 - 1085 2021年03月

We experimentally demonstrate that the Mosquito method is capable of fabricating single-mode polymer optical waveguides with multiple cores while maintaining an identical mode-field diameter among them. The Mosquito method we developed is a technique to form circular cores in polymer waveguides using a commercially available microdispenser and multi-axis syringe scanning robot. However, the core shape tends to deteriorate from a circle because of the monomer flow due to the needle scan. We also demonstrate both theoretically and experimentally for the first time in this paper that the needles with a tapered outer form or just titled straight needles enable to form cores with a high circularity even if those cores are dispensed on any heights from the substrate surface.

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Multi-Channel Single-Mode Polymer Waveguide Fabricated Using the Mosquito Method

Yakabe S., Matsui H., Kobayashi Y., Saito Y., Manabe K., Ishigure T.

Journal of Lightwave Technology （Journal of Lightwave Technology） 39 （ 2 ） 547 - 556 2021年01月

ISSN 07338724

We experimentally demonstrate that the Mosquito method is capable of fabricating polymer optical waveguides with single-mode cores. The Mosquito method we developed is a technique to form planar polymer waveguides using a commercially available microdispenser. In this article, the flow of the core monomer dispensed from the tip of the needle is simulated using fluid analysis software. The results show that the shape of the needle periphery significantly affects the fabrication of perfectly circular cross-sectional cores. In addition, we demonstrate that the Mosquito method is capable of reducing the MFD variation to 0.4 μm. We find such a small MFD fluctuation is comparable to that of typical single-mode optical fibers.

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