Published papers

© 2018 IEEE. In this paper, required specifications to a polymer waveguide based compact restricted mode launch (RML) device for multimode fibers are investigated. We confirm that a smaller spot size on the MMF launch end is necessary to enhance the effective modal bandwidth (EMBc), whereas a lower numerical aperture does not always allow the high EMBc. In addition, we determine the design guideline of polymer waveguide based RML exciters using the beam propagation method simulation.

© 2018 IEEE. We investigate direct implementation of polymer optical waveguides on a chip of surface emitting light sources (VCSEL). After confirming the position accuracy of the core, the core is successfully formed on the chip.

© 2018 IEEE. We develop a fabrication method of polymer optical waveguide in which the cores are aligned in the vertical direction to the substrate. Applying lightwave propagation simulation, several fabrication processes are investigated to realize a low-loss lens-free optical coupler to multimode fibers (MMF). Finally, an about 750-μm long graded-index core is directly formed on a VCSEL chip by which high coupling efficiency between the VCSEL and MMF is attained.

© 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.

© 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.

© 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.

© 2018 IEEE. We have proposed the Mosquito method to fabricate polymer optical waveguides with graded-index (GI) circular cores and demonstrated their excellent optical property. We have employed glass substrate which has a smooth surface for the waveguide fabrication using the Mosquito method. However, waveguides integrated on PCBs are expected for the on-board optical interconnection applications. The Mosquito method have a capability to directly fabricate waveguides on PCBs.In this paper, optical waveguides are fabricated on PCBs directly using FR-4 substrates which are a standard PCB. Here, the waveguide facet termination process is very important. Generally, waveguide ends are cut with the PCB using a dicing saw or polished after fabricating the waveguides separately from PCBs. In this paper, we propose a new waveguide facet termination process, which could be involved in the Mosquito method, and report the improvement of coupling efficiency to other optical components because the waveguide ends have sufficiently smooth surfaces.

© 2018 IEEE. In this paper, we represent an innovative technology for integrating optical devices: direct fabrication for polymer optical waveguide in a PMT ferrule, a ferrule for polymer waveguides connected with a mechanically transferable (MT) connector using the Mosquito method.

© 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.

© 2018 IEEE. For further increase of data rate in multimode fiber (MMF) links widely deployed in datacenters, wavelength division multiplexing (WDM) transmission technology is expected to be introduced. In this paper, we propose a Y-branched polymer waveguide with graded-index core for optical coupler in the MMF WDM links. The low loss structure of the Y-branched polymer waveguide is designed applying BPM simulation, and designed waveguide structures are actually fabricated using an imprint method to confirm their applicability to a low-loss optical coupler in MMF WDM links.

© 2019 IEEE. In this paper, we investigate the fabrication conditions for a polymer waveguide type multiplexer in mode division multiplexing links applying the Mosquito method. A Mach-Zehnder interferometer shaped single-mode waveguide is fabricated and almost 100% light transition by mode coupling is observed at 1550 nm.

© 2018 IEEE. Single-mode polymer optical waveguides applicable to silicon photonics technologies are fabricated using the imprinting method. Organic-inorganic hybrid resins are applied to fabricate the waveguides with low propagation loss at longer wavelengths and with high thermal resistance. The obtained optical waveguides have a graded refractive index distribution, by which the single-mode condition could be satisfied with a larger core size.

© 2019 IEEE. We have developed the Mosquito method for fabricating polymer optical waveguides. By using the Mosquito method, three-dimensional array of circular cores with graded-index (GI) profile can be formed. In this paper, to realize an effective coupling element for multicore fibers (MCF) and singlemode fibers, fan-in/out polymer optical waveguides are focused. For low-loss fan-in/out waveguide, the Mosquito method is applied where the fabrication conditions are investigated to improve the optical properties in multiple cores. Furthermore, fan-in/out structure for 7-core MCF is successfully fabricated.

© 2019 IEEE. For low-loss connection between silicon waveguides and conventional single-mode fibers, single-mode tapered polymer optical waveguides are fabricated using the Mosquito method, which work as a spot-size converter (SSC). In this research, the axially tapered shaped core is formed by accelerating the needle scan during the core dispense. In addition, the degradation of cross-sectional core shape from circle to ellipse is addressed by using a curved needle. The fabricated 12-mm long tapered waveguide with perfect circular core cross section exhibits an effective MFD conversion from 4.1 μm to 8.1 μm.

© 2018 IEEE. In this paper, Y-branched multimode polymer optical waveguides are fabricated using the Mosquito method for applying them to multiplexing (MUX) devices for WDM transmission.

© 2018 IEEE. In this paper, a compact restricted mode launch device for multimode fibers (MMFs) using graded-index polymer optical waveguide is designed and fabricated. We focus on an axially tapered shaped structure and demonstrated that the tapered structure could improve the effective modal bandwidth of MMF. Moreover, the optimum tapered structure is investigated using the beam propagation method simulation.

© 2020, The Author(s). Sapphirinid copepods, which are marine zooplankton, exhibit tunable structural colors originating from a layered structure of guanine crystal plates. In the present study, the coloring portion of adult male of a sapphirinid copepod, Sapphirina nigromaculata, under the dorsal body surface was characterized to clarify the regulation and actuation mechanism of the layered guanine crystals for spectral control. The coloring portions are separated into small domains 70–100 µm wide consisting of an ordered array of stacked hexagonal plates ~1.5 µm wide and ~80 nm thick. We found the presence of chitin-based honeycomb frameworks that are composed of flat compartments regulating the guanine crystal plates. The structural color is deduced to be tuned from blue to achromatic via yellow and purple by changing the interplate distance according to vital observation and optical simulation using a photonic array model. The framework structures are essential for the organization and actuation of the particular photonic arrays for the exhibition of the tunable structural color.

© 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.

© 2018 IEEE. We experimentally investigate the optical properties of single-mode polymer optical waveguides fabricated using two fabrication methods: The direct curing method and the Mosquito method. We demonstrate the characteristic differences between step-index square core single-mode waveguides and graded-index circular core single-mode waveguides composed of the same polymer materials.

© 2020, Springer Nature Singapore Pte Ltd. In this paper, Europium Aluminum Benzyl Methacrylate (Eu–Al/BzMA) optical waveguide amplifier is fabricated with multiple cores of 50 μm diameters by a unique procedure known as the Mosquito method which, utilized a micro-dispenser desktop machine. The waveguides which used the optimum dispensing criteria to fabricate desired core diameter with high precision are then optically tested. The highest optical gain of 1.08 dB/cm with 0.77 dBm/cm insertion loss has been demonstrated in this device at 617 nm amplification wavelength. Suppression of concentration quenching, high compatibility with other materials, ease of fabrication, and low cost make such rare-earth-metal ion-incorporated polymer waveguide amplifiers suitable for providing gain in many integrated optical devices in the communication area.