Papers - Ishigure, Takaaki

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 2025.01

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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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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 2024.07

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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 )  2024.02

ISSN  24058440

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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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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

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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

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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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Low-loss Subminiature Multimode Branched Polymer Optical Waveguide

Atsumi K., Azuma K., Ishigure T.

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

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We design subminiature multimode 1x2 and 1x4 branched polymer optical waveguides with circular cores, and then applying a new needle-scan path to the Mosquito method to experimentally fabricate low-loss waveguide couplers.

Loss Reduction of Single-mode Y-branched Polymer Optical Waveguide for MUX/DEMUX Devices in Mode Division Multiplexing Links

Sakai S., Ishigure T.

13th IEEE CPMT Symposium Japan: Innovation of Packaging Technology for Advanced Heterogeneous Integration, ICSJ 2024    200 - 203 2024

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Using the Mosquito method, we fabricate asymmetric single-mode Y-branched waveguides applicable to MUX/DEMUX devices for MDM technology. In order to reduce the insertion loss of Y-branched waveguides, we reexamine the fabrication conditions of symmetric single-mode Y-branched waveguides.

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Fixed Connection of Single-Mode Polymer Optical Waveguide with Single-Mode Optical Fiber

Toshida S., Ishigure T.

13th IEEE CPMT Symposium Japan: Innovation of Packaging Technology for Advanced Heterogeneous Integration, ICSJ 2024    164 - 165 2024

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We demonstrate forming a waveguide module by adhering a core in a polymer waveguide and a single-mode fiber (SMF) to stabilize the connection at high temperature. We confirm that the connections are stably maintained at 86°C.

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Fabrication of GI core polymer optical waveguides enabling low loss with small bend radius (~1 mm) using high Δ resins

Karakawa M., Ishigure T.

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

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In this paper, we fabricate GI-core multimode polymer optical waveguides with remarkably high Δ (~0.069) applying the Mosquito Method, by which the bending loss as low as 0.4 dB under 1-mm bending radius is attained.

Evaluation and Analysis of Polarization Dependent Polymer Optical Waveguide Characteristics

Wakabayashi T., Ishigure T.

13th IEEE CPMT Symposium Japan: Innovation of Packaging Technology for Advanced Heterogeneous Integration, ICSJ 2024    196 - 199 2024

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We design a measurement system to evaluate polarization dependent characteristics of polymer optical waveguides fabricated by the Mosquito method to be applied to a coupler between a single-mode fiber and silicon photonics chip. We observe the dependence of birefringence in single-mode polymer waveguides on their numerical aperture.

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Direct Connection of Multimode Polymer Waveguide and Multimode Fibers Using the Mosquito Method

Nakamura T., Ishigure T.

13th IEEE CPMT Symposium Japan: Innovation of Packaging Technology for Advanced Heterogeneous Integration, ICSJ 2024    154 - 155 2024

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In this paper, we investigate the monomer dispensing conditions for the Mosquito method to accurately arrange the cores on the desired positions. Then, direct connection of waveguide core and multimode fiber is realized with the Mosquito method.

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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

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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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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

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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.

Step and graded-index core-based polymer multimode interference splitters for photonic integrated circuits

Rasel M.O.F., Afsary N., Alam M.K., Tasnim F., Sakib M.N., Hatai R., Ishigure T.

Optik 290 2023.10

ISSN  00304026

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This paper demonstrates step-index (SI) and graded-index (GI) core-based multimode interference (MMI) splitters realized with polymer materials for photonic integrated circuits (PICs). These SI and GI index-based MMI splitters guide the input light through the multimode waveguide following the self-imaging principles and demonstrate the multiple outputs with the same uniformity when the self-imaging length is obtained. We numerically design and develop (1 ×5) MMI splitters using the beam propagation method (BPM), and we use the RSoft CAD BeamPROP solver for the structural design and waveguide characterization. The structures of the SI and GI MMI splitters are optimized by investigating the structural parameters, particularly the width and length of the multimode waveguide and the core spacing between the output ports with the maximum uniform intensity at the self-imaging length. We also compare the structural design and optical properties of the SI and GI MMI waveguides. The excess losses of the SI MMI splitter are 1.09 and 1.12 dB for transverse electric (TE) and transverse magnetic (TM) modes, respectively, while for the GI MMI splitter, the losses are 0.57 dB and 0.56 dB for TE and TM modes, respectively at 1.55 µm. The power splitting efficiency for the SI MMI splitter is 77%, and for the GI MMI splitter, it is 88%. We also investigate the polarization dependence loss (PDL) for both MMI splitters, and the losses for the SI and GI MMI splitters are 0.024 dB and 0.004 dB, respectively.

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Fabrication of Circular Cross-Section Microchannels with 3-D Lattice Arrangement and Their Use as On-Off Valves

Uehara K., Hori Y., Ishigure T.

Micro 3 ( 3 ) 620 - 631 2023.09

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In this paper, circular cross-section microchannels with 3-D lattice arrangements are designed and fabricated using the Mosquito method in order to construct on-off valves. The 3-D microchannels with on-off valves consist of two types of lines: the flow lines for chemical liquid flow and the control lines to activate the valves. We confirmed that both a circular cross-section and a PDMS with low elastic modulus used as the microchannel material contribute to a valve that can be closed with a lower pressure. Then, we demonstrated liquid flow to evaluate the functionality of the valve. Fluorescein solution was flown into a flow line. We found that the fluorescence intensity decreases at the intersection between the flow and control lines when the flow line is closed by the inflation of the control line, experimentally confirming the functionality of the valve microchannels fabricated via the Mosquito method.

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Graded-index core-based polarization beam splitters realized with symmetric polymer directional couplers

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

Optics Continuum 2 ( 5 ) 1040 - 1052 2023.05

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In this paper, we design and demonstrate polymer-based polarization beam splitters realized with parabolic graded-index (GI) directional couplers at 1550 nm. We design and investigate these beam splitters by using the beam propagation method (BPM) and the RSoft CAD BeamPROP solver is used for model design and characterization. We study the splitting ratio of 50:50 and 100:0 of these beam splitters for both transverse electric (TE) and transverse magnetic (TM) modes of the polarized light. In particular, the 50:50 beam splitters exhibit an output efficiency of 95% due to the absence of polarization. However, in the presence of the polarization effect, the polarization dependency is analyzed and manipulated successfully, and the output efficiency increases by approximately 98% at an incident angle of 31° due to the polarized launch field. Moreover, the 100:0 beam splitters act as the switching devices realized with parabolic GI polymer directional couplers. The insertion losses of the GI beam splitters are 0.162 dB and 0.186 dB, while the excess losses are 0.148 dB and 0.149 dB for TE and TM modes, respectively. Also, the polarization extinction ratio (PER) of the 100:0 beam splitters is >25 dB and >20 dB for TE and TM modes, respectively.

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VCSEL-based optical transceiver with a 90°-bent graded-index core polymer waveguide coupler for 25.78-Gb/s transmission

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

Optics Continuum 2 ( 5 ) 998 - 1012 2023.05

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In this paper, we propose a low-loss assembly of optical elements [vertical cavity surface emitting laser (VCSEL)/photodiode (PD)] and a 90°-bent graded-index (GI) core polymer optical waveguide for compact high-speed optical transceivers. The air gap between the 90°-bent GI-core waveguide and VCSEL/PD chips are filled with a high-index resin, and we demonstrate a reduction not only of the Fresnel reflection loss but also of the coupling loss due to the lower divergence angle of VCSEL and fiber output beams. In this paper, the core size and NA of the 90°-bent GI-core in the polymer waveguide are redesigned to match the specific launch conditions realized with the gap filled with resins, resulting in theoretical estimates of insertion losses as low as 0.82 dB and 1.38 dB for the waveguides on the transmitter and receiver sides, respectively. Such low insertion losses are obtained not by step-index core but GI core waveguides. After redesigning the structure, 90°-bent GI-core polymer waveguides with a bending radius of 1 mm are experimentally fabricated using the Mosquito method, and we experimentally demonstrate that the insertion loss of the waveguide can be reduced by about 4 dB when the 100-µm air gap is filled with an optical adhesive (na = 1.51). In addition, an error-free 25.78-Gb/s data transmission is successfully demonstrated over a 100-m MMF link using the fabricated VCSEL based transceivers with 90°-bent GI core polymer optical waveguides.

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Unique Optical Connect Structure with Polymer Waveguide Fabricated by the Mosquito Method

Furuta Y., Kondo F., Ito A., Ichinose R., Kaneda H., Fujii T., Ishigure T.

2023 IEEE CPMT Symposium Japan, ICSJ 2023    41 - 44 2023

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We develop a unique optical connect structure with polymer waveguide fabricated by the Mosquito method for Co-Packaged Optics. We present the details of this optical connect structure and evaluation results of prototype waveguide.

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Temperature Dependence of Coupling Loss from SMF to Polymer Optical Waveguides with Various Refractive Index Profiles

Kinoshita R., Ishigure T.

2023 IEEE CPMT Symposium Japan, ICSJ 2023    172 - 175 2023

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In this paper, we theoretically estimate the temperature dependence of coupling loss between single-mode (SM) polymer optical waveguides and general-purpose SM fiber (SMF), and discuss about the applicability of polymer optical waveguides to co-packaged optics (CPO). Although SM polymer optical waveguides are expected to be applied as an element of CPO, their small cores require precise mode-field adjustment with precise alignment of the cores. The mode-field and alignment positions of polymer waveguides are conce1ed to be affected by their operation temperature, particularly when integrated with Si photonics chips that could be a heat source. Simulation results show that the properties are maintained even under high-temperature operation.

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Tactile Pressure Sensor Based on Flexible Polymer Optical Waveguides Fabricated by the Mosquito Method

Yin Y., Ishigure T.

2023 IEEE CPMT Symposium Japan, ICSJ 2023    176 - 179 2023

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In this paper, a polymer-based optical waveguide sensor is created to address several issues in optical fiber-based sensors. The unique feature of our optical waveguide is its 3-D core arranged design fabricated using the Mosquito method to which poly dimethyl siloxane (PDMS) is applied as the cladding for a flexible tactile sensor. The core monomer is dispensed into the PDMS monomer to have a 3D lattice structure. We demonstrate that the fabricated waveguide sensors exhibit a high repeatability of the pressure sensing. We find that the measurement range is from 0 MPa to 0.164 MPa when an organic inorganic hybrid resin, NP-C01-KO is used as the main core material. By examining the effect of the numerical aperture and the core size on the sensitivity, we confirm that bending loss could cause the output power variation when a load is applied to the sensor.

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