Published papers

© 2009-2012 IEEE. We develop a graded-index plastic optical fiber (GI POF) that can significantly stabilize a multimode fiber (MMF) link with a vertical-cavity surface-emitting laser (VCSEL) subject to external optical feedback. It is demonstrated that the dominant mechanism for this stabilization effect is the strong mode coupling of the GI POF, which is closely related to the polymer-specific microscopic heterogeneities in the GI POF core material. Such mode coupling decreases correlation between the problematic reflected light field and VCSEL cavity field, increasing tolerance of the MMF link for external optical feedback. Our developed GI POF with specific microscopic heterogeneities prevents the external-optical-feedback-induced critical destabilization observed for silica GI MMFs. These results suggest that the stabilization effect can be controlled by microscopic properties regardless of the fiber attenuations and core refractive indices.

© 1983-2012 IEEE. Internet traffic continues to grow with the increase of network-connected smartphones, tablets, televisions, and monitoring devices in the Internet-of-Things (IoT) era. This trend will be significantly accelerated by the introduction of ultrahigh-definition (UHD) imaging technologies in various applications, and existing optical networks including datacenter networks are under urgent development to accommodate this traffic. However, optical fibers have not been introduced into households located in optical network terminal areas, even though UHD device connections require decompressed high-volume data transmission at more than 100 Gb/s, where a multilevel modulation scheme is vital. In UHD applications, very short optical cables (typically less than several meters) are connected and disconnected by consumers in a manner similar to metal interface cables. Under such conditions, a data transmission quality is predominantly limited by noise and instability rather than bandwidth and loss. Here, we propose low-noise graded-index plastic optical fibers (GI POFs) that enable significantly stable and robust data transmission through strong mode coupling, whose mechanism is fundamentally different from that of silica optical fibers. The low-noise GI POF link eliminates the need for the precise fiber alignment, angled fiber facets, and optical isolators typically used in conventional links. Our proposed GI POF material paves the way for quick optical fiber connections for multilevel UHD video transmission, becoming the first 'capillaries of light' from optical network terminals in the IoT era.

© 1983-2012 IEEE. This paper presents a study on the influence of the polarization of the pump beam on the emission properties of dye-doped polymer optical fibers. The fiber samples, which are pumped transversely with linearly polarized light, are graded-index polymer optical fibers doped with rhodamine 6G. The variation of the intensity and angular distribution of the output emission are theoretically and experimentally analyzed as the polarization direction of the pump is changed. The analysis is carried out both in the regime of fluorescence and in the regime of amplified spontaneous emission. It is shown that a pump polarization perpendicular to the fiber symmetry axis yields not only higher emission efficiency but also narrower axial angular width. The effect of the polarization of the pump beam on the properties of the amplified spontaneous emission is also measured, including its threshold-like energy, relative efficiency, and optical gain. The results indicate that the pump polarization determines the light-emitting performance of dye-doped polymer optical fibers.

© 2018 The Author(s). We investigate the influence of reflection noises in graded-index plastic optical fiber link based on ballpoint-pen interconnect. The results suggest that the link quality tend to improve through reflection noises reduction despite system loss increase.

© 2019 OSA. We develop plastic optical fibers that significantly improve TV transmission qualities compared with conventional multimode fibers despite their higher attenuation. This improvement is attributed to mode coupling that is closely related to microscopic core-material properties.

© 2019 IEEE. We experimentally demonstrate that a graded-index plastic optical fiber (GI POF) can significantly reduce transmitted signal distortion caused by the nonlinear response of a multimode fiber (MMF) link based on a vertical-cavity surface-emitting laser (VCSEL). The low distortion of the signal transmission is attributed to the strong mode coupling in the GI POF, which suppresses the increment in signal distortion due to the external optical feedback, by reducing the self-coupling of problematic back-reflected light into the VCSEL cavity. The strong mode coupling is closely associated with polymer-specific microscopic heterogeneous structures in the fiber core materials, suggesting that the signal distortion can be further reduced by controlling the microscopic properties. The nonlinear distortion reduction effect of our developed GI POF will be invaluable for next-generation MMF links based on multilevel modulation in the ultrahigh-definition era.

© 2019 Elsevier Inc. We describe a comprehensive analysis of the nano-creep deformation of an epoxy adhesive used in physical-contact optical fiber connectors. To design a highly reliable multicore fiber connector and predict the long-term reliability of commercially installed optical connectors, we focus on the change in fiber withdrawal, which is a key parameter for achieving physical-contact connection. We also propose an adhesive creep model that includes long-term time dependence by detailing through a finite element analysis the parameters that influence the fiber withdrawal, such as shear stress with connection, thermal stress, residual stress, swelling, and cure shrinkage. The measurement results for fiber withdrawal under several environmental conditions provided in this paper support the behaviors considered in our proposed model. From our obtained short-term results and rheological approach, we predict the nano-creep deformation observed in the connector over the long term by applying the time-temperature superposition principle, and discuss the correspondence with exposure test results. Our verified mechanism and estimated values of creep deformation prove the high reliability of the optical connectors and also provide guidelines for determining the need to update installed connectors and for designing future connection devices such as physical-contact multicore fiber connectors.

© 2018 International Display Workshops. All rights reserved. We proposed the novel film, random depolarization film, which is the polymer film doped with the birefringent crystal particles. With using this film, we succeeded to solve the "blackout problem " of displays and to achieve much lower chromaticity change with polarized sunglasses.

© 2020 Optical Society of America We developed a graded-index plastic optical fiber (GI POF) that enables lower-noise radio frequency (RF) transmission than conventional multimode fibers for short-distance household applications (<100 m). It is shown that reflection noise degrades RF transmission, regardless of the carrier frequency, through the spurious generation that accompanies the RF modulation of a vertical-cavity surface-emitting laser. The GI POF with distinctive mode coupling, which is closely related to its microscopic polymer structure, suppresses noise and spurious generation to improve transmission quality. Our low-noise radio-over-GI-POF technology will offer significant advantages for optical wiring systems for broadcast and communication in small- and medium-scale buildings.

© 1989-2012 IEEE. We demonstrate that a graded-index plastic optical fiber (GI POF) enables higher-quality radio-over-fiber (RoF) transmission of an orthogonal frequency-division multiplexing (OFDM) signal, compared with a conventional multimode fiber, for short-distance household applications (< 100 m). It is shown that the improvement in OFDM signal transmission, using the GI POF, can be attributed to the reduction in noise and intermodulation distortion, owing to the external optical feedback from the transmission fibers. The low noise and low distortion in the signal transmission are mainly due to the strong mode coupling in the GI POF, which is closely related to the microscopic heterogeneous structures in core polymer materials. The developed GI POF will be invaluable for RoF networks in households as a solution for indoor broadband wireless communications in the upcoming 5G era.

© 2019 Elsevier Inc. We describe a new physical-contact optical fiber connector/receptacle that can withstand a solder-reflow process with a maximum temperature of 260 °C for advanced pluggable transceiver packaging such as the co-packaging of photonic and electronic chips using the reflow process. We experimentally clarify the problems that occur in the conventional simplex optical connector through the reflow process while discussing the glass-transition behavior of the adhesive used in the connector. We then present an improved receptacle structure with glass-based ferrules whose coefficients of thermal expansion are closer to that of the fiber compared to the conventional zirconia ferrule. We demonstrate through testing that our proposed receptacle results in a dramatic decrease of permanent fiber withdrawals after the reflow process. The proposed connector, which is composed of a glass-ceramic ferrule, a polyimide tube, and a mechanical clip, achieved physical-contact connection and maintained satisfactory connection and return losses of below 0.3 dB and over 45 dB, respectively, even after six reflow processes. We examined the withdrawal behaviors for both the zirconia and the glass-ceramic ferrules during reflow based on the online measurement of connection and return losses, and observed the multiple reflections caused by the change in the air-gap width between the mated connectors. We also confirmed that the developed simplex optical connectors based on the glass-ceramic ferrule yielded sufficient environmental durability even after multiple reflow processes.

© 2020 SID. We have developed a 17.3-inch 8K wide color gamut in-plane switching LCD (IPS-LCD) with a polarized laser backlight. By applying a zero–zero-birefringence polymer, the polarized laser backlight emits polarized light with 88% polarization. The IPS-LCD with the developed polarized laser backlight achieves a wide color gamut with high efficiency.

© 2020 SID. Our proposal, the random depolarization film (RDF), prevents blackout and color change of the display image viewed through polarized sunglasses. We demonstrated that the RDF doped with micro-sized particles realized the real-color display without the blackout and the color change, and the clear display.

© 2020 SID. We propose two types of temperature-independent zero–zero-birefringence polymers (TIZZBPs), which have different Tgs of 194°C and 156°C. These TIZZBPs also exhibit sufficient mechanical strength and high transparency. These TIZZBPs will achieve real-color images not only for vehicle-mounted displays but also for flexible displays.