論文 - 小池　康博

Random depolarization film design for real-color displays

Sasaki S., Udono M., Koike Y.

Applied Optics （Applied Optics）  61 （ 3 ） 669 - 675 2022年01月

ISSN  1559128X

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Liquid crystal displays and organic light-emitting diode displays emit polarized light through polarizers and quarter-wave plates, which cause blackout and color change problems when the displays are viewed through polarizers, such as polarized sunglasses. Random depolarization films (RDFs) are polymer films doped with calcite particles, which randomize the polarization of light emitted from displays to resolve polarization problems. To realize displays without any color change, we investigate the retardation values and fabrication conditions required for RDFs. Analysis of the transmittance spectra and interference colors of different RDFs suggested that retardation values of approximately 600–1200 nm are sufficient to realize real-color displays. In addition, the color change measurements of displays with the RDFs revealed that an optimal dopant particle size exists and that the RDFs doped with 3.6 and 7.3 µm calcite particles achieved chromaticity changes of less than 0.02 for all 24 colors in the Macbeth chart.

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Error-free PAM-4 transmission by a high-speed plastic optical fiber without forward error correction

Koike Y., Muramoto K.

Optics Letters （Optics Letters）  46 （ 15 ） 3709 - 3712 2021年08月

ISSN  01469592

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This Letter reports, to the best of our knowledge, the first study in which error-free four-level pulse-amplitude modulation (PAM-4) transmission has been achieved using a graded-index plastic optical fiber (GI POF) without the use of forward error correction (FEC) techniques, at a high data rate (>50 Gb/s), for short-reach applications (10 m). The GI POF that is developed has the characteristic microscopic heterogeneities in the fiber core material, which provide distinct mode coupling and significantly stabilize PAM-4 data transmission. The results of the study in this Letter indicate that the GI POF achieves highly stable PAM-4 transmission without the need for the current FEC techniques, which seriously increase the communication delay and power consumption of the transmission systems. Our GI POF material is paving the way for “material changes the system” approaches for achieving unprecedented optical interconnects in real time at a high speed and with low power consumption.

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Real-color displays realized by randomized polarization

Sasaki S., Udono M., Koike Y.

Applied Optics （Applied Optics）  60 （ 11 ） 3108 - 3113 2021年04月

ISSN  1559128X

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This study achieves real-color displays using a randomizing effect based on the concept of "natural light."At present, most displays emit linearly polarized light, which causes essential blackout and color degradation problems when the displays are viewed through polarizers such as sunglasses. To address this, complex polarization-control technologies are added to existing displays, but the problems remain unresolved. In contrast, this study randomizes the polarization using a polymer film called a random depolarization film (RDF) that is doped with specific birefringent crystal particles. The RDF placed on a display reproduces colors that are very close to the natural colors seen in reality without the need for complex polarization technologies.We believe that it has the potential to change the approach to color-reproducing technology for displays.

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Proposal of novel temperature-independent Zero–Zero-birefringence polymer with high heat-resistance

Watanabe K., Kobayashi Y., Koike Y.

IEICE Transactions on Electronics （IEICE Transactions on Electronics）  E104C （ 2 ） 59 - 63 2021年02月

ISSN  09168524

　概要を見る

Copyright © 2021 The Institute of Electronics, Information and Communication Engineers. Temperature-independent zero–zero-birefringence polymer (TIZZBP), which exhibits very small birefringence over the wide temperature range, is required to realize real-color images for displays, particularly vehicle-mounted displays. Previously, a TIZZBP was synthesized, but they did not put into practical use because of their too complex composition and low mechanical strength. In this paper, we propose a practical TIZZBP that has high heat resistance, high transparency and sufficient mechanical strength, using a simple binary copolymerization system. Our proposed novel polymer exhibits very low photoelastic birefringence and very low orientational birefringence. Both types of birefringence of this TIZZBP satisfy the negligible levels for displays, which are defined as follows: the absolute values of photoelastic coefficient and intrinsic birefringence are less than 1 ×10−12 Pa−1 and 1 ×10−3, respectively. In addition, temperature dependency of orientational birefringence was very low. Orientational birefringence satisfies the negligible level all over the temperature range from around −40◦C to 85◦C. This temperature range is important because it is the operational temperature range for vehicle-mounted display. Furthermore, our proposed novel TIZZBP showed high heat resistance, high transparency and sufficient mechanical strength. The glass transition temperature was 194◦C. The total light transmittance and the haze value is more than 91% and less than 1%, respectively. The tensile strength of non-oriented films was 35 ∼ 50 MPa. These results suggest our proposed novel TIZZBP has high practicality in addition to very low birefringence. Therefore, this TIZZBP film will be very useful for various displays including vehicle-mounted displays and flexible displays.

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Design of random depolarization film with random retardation for real-color displays

Sasaki S., Udono M., Koike Y.

Digest of Technical Papers - SID International Symposium （Digest of Technical Papers - SID International Symposium）  52 （ 1 ） 1283 - 1286 2021年

ISSN  0097966X

　概要を見る

Our proposal, the random depolarization film (RDF) is highly efficient in preventing color change problem of LCD and OLED displays. We designed the RDF that realizes real-color displays by considering the retardation. The RDF with random retardation above 600 nm achieved much lower color change that human eyes cannot recognize.

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Random Depolarization Film Doped with Calcite Microparticles for Clear Real-Color Displays

Sasaki S., Udono M., Koike Y.

26th Microoptics Conference, MOC 2021 （26th Microoptics Conference, MOC 2021）  2021年

　概要を見る

Random depolarization film, a polymer film doped with birefringent particles, can resolve blackout and color change problems of existing displays. This study optimized the dopant particle size with respect to image sharpness and color change of the display. Calcite microparticles improved the sharpness and color change, and realized real-color displays.

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Low-Noise Graded-Index Plastic Optical Fiber Achieved by Specific Copolymerization Process

Akashi T., Inoue A., Koike Y.

Journal of Lightwave Technology （Journal of Lightwave Technology）  39 （ 11 ） 3553 - 3559 2021年

ISSN  07338724

　概要を見る

Ultra-high-definition (UHD) technologies have recently received attention on account of their practical applications in consumer electronics. UHD devices require uncompressed video transmission at a data rate exceeding 100 Gb/s; thus, an optical fiber connection is essential. In consumer applications, optical fibers are very short. Moreover, their connections must permit variations in the fiber alignment, which accommodates rough handling by consumers. Under this condition, the transmitted signal quality is significantly degraded owing to noise and instabilities that strongly depend on the fiber alignment conditions in optical modules and connectors. Therefore, graded-index plastic optical fibers (GI POFs) are promising optical cables for consumer applications because of their flexibility, safety, and high bandwidth. Recently, the authors experimentally demonstrated that GI POFs can reduce interferometric noise, such as modal noise and multipath interference noise, in a multimode fiber link based on a vertical-cavity surface-emitting laser (VCSEL). This noise reduction effect results from strong mode coupling of GI POFs, which is closely related to microscopic heterogeneous structures of a core polymer matrix. In this paper, a control method of mode coupling using the copolymerization process for fiber core materials is proposed. The formation of composition fluctuations by copolymerization increases the mode coupling in the GI POF core. It thereby enables highly stable and robust data transmission with a large fiber misalignment tolerance in a VCSEL-based multimode fiber link. The proposed method for mode coupling control is expected to contribute to household optical communication systems in the upcoming UHD era.

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Noise and Distortion Reduction in OFDM Radio-Over-Fiber Link by Graded-Index Plastic Optical Fiber

Muramoto K., Inoue A., Koike Y.

IEEE Photonics Technology Letters （IEEE Photonics Technology Letters）  32 （ 13 ） 835 - 838 2020年07月

ISSN  10411135

　概要を見る

© 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.

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Low-noise radio over graded-index plastic optical fiber

Inoue A., Koike Y.

Optics Letters （Optics Letters）  45 （ 12 ） 3192 - 3195 2020年06月

ISSN  01469592

　概要を見る

© 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.

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Reflowable optical connector with glass-ceramic ferrule for advanced pluggable transceiver packaging

Shikama K., Koike Y.

Optical Fiber Technology （Optical Fiber Technology）  54 2020年01月

ISSN  10685200

　概要を見る

© 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.

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A wide color gamut lcd with a polarized laser backlight

Komura S., Okuda K., Onoda K., Kijima H., Tagaya A., Kikutani T., Koike Y.

Digest of Technical Papers - SID International Symposium （Digest of Technical Papers - SID International Symposium）  51 （ 1 ） 5 - 8 2020年

ISSN  0097966X

　概要を見る

© 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.

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Proposal of novel polymer materials with no birefringence over wide temperature range

Watanabe K., Yuma K., Koike Y.

Digest of Technical Papers - SID International Symposium （Digest of Technical Papers - SID International Symposium）  51 （ 1 ） 1600 - 1602 2020年

ISSN  0097966X

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© 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.

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Analysis of random depolarization films with birefringent micro particles for liquid-crystal and oled displays

Sasaki S., Udono M., Koike Y.

Digest of Technical Papers - SID International Symposium （Digest of Technical Papers - SID International Symposium）  51 （ 1 ） 1596 - 1599 2020年

ISSN  0097966X

　概要を見る

© 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.

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Analysis of nano-creep deformation of epoxy adhesive in optical fiber connector for long-term reliability prediction

Shikama K., Aratake A., Koike Y.

Optical Fiber Technology （Optical Fiber Technology）  52 2019年11月

ISSN  10685200

　概要を見る

© 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.

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Nonlinear Distortion Reduction Effect of Graded-Index Plastic Optical Fiber

Muramoto K., Inoue A., Koike Y.

IEEE Photonics Technology Letters （IEEE Photonics Technology Letters）  31 （ 10 ） 791 - 794 2019年05月

ISSN  10411135

　概要を見る

© 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.

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Unconventional plastic optical fiber design for very short multimode fiber link

Inoue A., Koike Y.

Optics Express （Optics Express）  27 （ 9 ） 12061 - 12069 2019年04月

　概要を見る

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement We introduce a graded-index plastic optical fiber (GI POF) design for very short-distance household applications, in which the transmission quality is predominantly determined by system noise rather than the loss and bandwidth. The developed GI POF has strong mode coupling with low accompanying scattering loss, which is closely related to the specific microscopic heterogeneities in the core material. Such characteristic mode coupling significantly decreases reflection noise, improving the transmission quality compared with silica GI multimode fiber (MMF) for lengths below 30 m. Moreover, in the GI POF link, the transmission quality tends to improve with increasing fiber length, despite the increased loss and decreased bandwidth. This feature suggests that the system noise can be controlled by the microscopic heterogeneous properties of the GI POF for a very short MMF link, where the fiber loss and bandwidth are sufficiently low and high, respectively. This unconventional concept for optical-fiber design can advance fiber-optic communication in emerging applications in households located near optical network terminals.

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Low-Noise Radio over Plastic Optical Fiber for TV Broadcasting in Ultrahigh-Definition Era

Inoue A., Koike Y.

2019 Optical Fiber Communications Conference and Exhibition, OFC 2019 - Proceedings （2019 Optical Fiber Communications Conference and Exhibition, OFC 2019 - Proceedings）  Part F160-OFC 2019 2019年04月

ISSN  9781943580538

　概要を見る

© 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.

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Intrinsically Stabilized Plastic Optical Fiber Link Subject to External Optical Feedback

Inoue A., Koike Y.

IEEE Photonics Journal （IEEE Photonics Journal）  11 （ 1 ）  2019年02月

　概要を見る

© 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.

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Low-noise graded-index plastic optical fiber for significantly stable and robust data transmission

Inoue A., Koike Y.

Journal of Lightwave Technology （Journal of Lightwave Technology）  36 （ 24 ） 5887 - 5892 2018年12月

ISSN  07338724

　概要を見る

© 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.

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Development of Graded-Index Plastic Optical Fiber for Significantly Low-Noise Data Transmission

Inoue A., Koike Y.

European Conference on Optical Communication, ECOC （European Conference on Optical Communication, ECOC）  2018-September 2018年11月

ISSN  9781538648629

　概要を見る

© 2018 IEEE. We develop plastic optical fibers (POFs) with microscopic material properties designed for stable data transmissions for ultrahigh-definition applications in households (<30m). In the POF link, transmission quality tends to be improved with increase in link length despite loss increase.

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