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Fujikura Technical Review

No.47 November, 2017

CONTENT

Non-metallic Aerial Distribution Optical Cables for FTTH Networks

One of the common practices to construct economical and efficient Fiber To The Home (FTTH) networks is to share “electric poles” by optical fiber networks and power lines. For safe deployment of optical cable close to power lines and lightning strike prevention, we have proposed the non-metallic FTTH networks solution.

To achieve the proposal solution, we have developed non-metallic self-supporting highdensity aerial distribution optical cables that allow easy and simple mid span access installation in a short time and non-metallic drop optical cables that are compatible with conventional field assembled connectors. In particular, the lineup of the aerial optical cables is now extend to 48-fiber. This paper presents the details of these new non-metallic optical cables.

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High-Numerical-Aperture Optical Fibers for Low-Loss Coupling with Silicon Photonic Waveguides

We have developed high-numerical-aperture (NA) single-mode fibers and polarization-maintaining fibers that are suitable for low-loss coupling with silicon photonic waveguides. They have a mode field diameter (MFD) of 4 μm to match those of the edge-coupling spot size converters (SSCs) formed in the silicon photonic waveguides. We utilized the thermally expanded core (TEC) technique to reduce the splice losses between the high-NA fibers and standard fibers with an MFD of 10 μm. Some dopants were co-doped into the inner cladding region of the TEC fibers, increasing the expansion speed of the fiber core. Lower-loss splicing was achieved by increasing the co-doping concentrations. The fiber coupling with the silicon photonic waveguides using an inverted tapered SSC was tested. The measured coupling loss was as low as 3 dB/2 facets using these fibers and it is possible to further reduce this loss.

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Low-Driving-Voltage Silicon DP-IQ Modulator

Silicon photonics is a promising technology to bring drastic reduction in cost and size for various kinds of optical devices. In this paper, we report a low-driving-voltage silicon dual polarization (DP) in-phase quadrature modulator especially for a digital coherent transmission system requiring low power consumption. The modulator includes a newly developed phase shifter and polarization multiplexing waveguide. The phase shifter employs a p-n junction formed in vertical direction, which enhances modulation efficiency and provides a low Vp of 2.5 V. The polarization multiplexing waveguide enables polarization rotation and combination at a low insertion loss of less than 0.5 dB in a broad wavelength range of C- and L-bands. A packaged modulator has exhibited high-speed modulations such as DP 16- and 32-quadrature amplitude modulations, and achieved 2000-km standard SMF transmission in DP quadrature phases shift keying well used in commercial optical fiber networks.

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Highly reflective materials processing by 3 kW single-mode Yb-doped fiber laser with 20-m long delivery fiber

High output power and a long delivery fiber are important requirements for many practical applications of a high power single-mode fiber laser. In Fujikura, a 3 kW all-fiber single-mode Yb-doped fiber laser with a 20-m long delivery fiber has been developed. The fiber length of 20 m is long enough to use our single-mode fiber laser in most of laser processing machines. Stimulated Raman Scattering (SRS), which is most important issue in high power single-mode fiber lasers, is well suppressed. The stokes light power is 30dB below the laser light power at the output power of 3 kW. Excellent beam quality is also confirmed. The M-squared factor is 1.3. In Bead on Plate (BoP) demonstration onto a pure copper, stable processing with deep penetration and narrow bead is achieved.

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Yttrium-based Coated Conductors With Artifitial Pinning Centers

Yttrium (Y) -based coated conductors (CCs) are known as helium-less materials and are expected to be applied to the systems such as MRIs and accelerators which need high critical currents (Ic). In this work, we fabricated Y-based CCs with artifitial pinning centers (APCs), which are known to improve in-field Ic, and uniform high in-field Jc by Hot-Wall heating PLD system.

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Silicone Module-type Termination with Salt Damage Resistance

Silicone module-type termination was developed to instead of ceramic-type termination that generally used in contamination conditions. Developed termination has divided skirt with under-ribs, it can be adapted to arbitrary voltage or environment. Sufficient performance has been confirmed by evaluation test.

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Fine-Electrode Foil for Particle Physics Experiment

Recently, various electronic devices have decreased in size and increased in functionality, as typified by smart phones. In step with this, flexible printed circuit (FPC) boards, which are used as a wiring material in these devices, have been making progress in production techniques, especially, to form finer and denser traces. Using Fujikura’s proprietary FPC production techniques, we are working on new products. As an example of these newly developed products, this report describes a fine-electrode foil, which is used in a detector for particle physics experiments.

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Two Chips Vertical Direction Embedded Miniaturized Package

Continuous efforts have been made to achieve seemingly conflicting goals of reducing the size of electronic devices and increasing their functionality, especially in the growing industries including those of wearable computers and medical and healthcare devices. To meet the needs in these areas, we have developed a die embedded package, called WABE (Wafer and Board Level Embedded) Package, which is thin and embedded with one IC chip, by combining a multilayer FPC technology and a thin WLP technology. This package is fabricated by a single step co-laminating process using conductive-paste-filled vias for establishing z-axis interlayer electrical connections. In addition, we also have developed a chip-stack embedded package that has two IC chips embedded vertically in a circuit board and put it to practical use for the first time in the world to meet the demand for smaller packages. This new chip-stack embedded package can be fabricated by almost the same process as a single IC embedded package. We evaluated the reliability of the package (4.35 by 3.00 with 0.40 mm thickness) with seven wiring layers and two EEPROMs embedded in a stacked configuration. We conducted MSL 3 (Moisture Sensitivity Level 3) test as pre-conditioning. After MSL3 test, these packages were put through a temperature cycle test, a temperature humidity bias test and a high temperature storage test. All the modules were tested for diode characteristics and functionality and met the requirements for the tests. We believe this chip-stack embedding technology is promising to downsize the footprint especially for a package with high functionality and a complex structure.

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High Performance Ultra Thin Heat Pipe Cooling Module for Mobile Hand Held Electronic Devices

In recent years, heat pipes have been widely used in various hand held mobile electronic devices such as smart phones, tablet PCs and digital cameras. With the development of technology these devices have different user friendly features and applications; which require very high clock speeds of the processor. In general, a high clock speed generates a lot of heat, which needs to be spreaded or removed to eliminate the hot spot on the processor surface. However, it is a challenging task to achieve proper cooling of such electronic devices mentioned above because of their confined spaces and concentrated heat sources. Regarding this challenge, we introduced an ultra-thin heat pipe; this heat pipe consists of a special fiber wick structure named as “Center Fiber Wick” which can provide sufficient vapor space on the both sides of the wick structure. We also developed a cooling module that uses this kind of ultra-thin heat pipe to eliminate the hot spot issue. This cooling module consists of an ultra-thin heat pipe and a metal plate. By changing the width, the flattened thickness and the effective length of the ultra-thin heat pipe, several experiments have been conducted to characterize the thermal properties of the developed cooling module. In addition, other experiments were also conducted to determine the effects of changes in the number of heat pipes in a single module. Characterization and comparison of the module have also been conducted both experimentally and theoretically.

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Effects of Magnetocaloric Wire on Increase in Magnetic Refrigeration Cycle

We are working on the development of an environment-friendly, next-generation magnetic refrigerator focusing on magnetic refrigeration technology. Since conventional magnetic refrigerators have the problem of insufficient cooling, we aim to develop a new system with increased cooling power by increasing their cycle frequency. To achieve the goal, we have developed a magnetocaloric material (MCM) consisting of thin wires with the world’s smallest diameter using wire drawing, which is one of Fujikura’s core technologies. As a result of using the wire-shaped MCM in a magnetic refrigerator and operating this device at a cycle frequency of 10 Hz, the system achieved the world’s top-level specific cooling power in a weak magnetic field of 0.6 T. This paper provides a summary of the results from experiments.

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