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  4. No.38 January,2009
Fujikura Technical Review

No.38 January,2009



A Multiband Antenna Consisting of One Element for Mobile Phone Applications
Compactness and multiband operation are usually required for antennas used in mobile phones. In addition, other features such as flexibility, light weight, simple structure, and low cost are also important for practical design. In this paper, we report a new multiband antenna which operates for the Global System for Mobile Communications (GSM:880-960 MHz), Digital Cellar System (DCS:1710-1880 MHz), Personal Communication Service (PCS:1850-1990 MHz), and Universal Mobile Terminal System (UMTS:1920-2170 MHz) bands. This antenna can be made of metal wires, plates, or thin films. From a fabricated antenna, it is shown that the antenna covers the four bands of GSM, DCS, PCS, and UMTS and has almost omni-directional radiation patterns at each band.
Photodarkening Phenomenon in Yb-Doped Fibers
Photodarkening phenomenon in ytterbium (Yb)-doped fibers is a serious issue for fiber lasers from a practical viewpoint. However, the mechanism of photodarkening has not been elucidated in detail yet. In the present paper, we report on the experimental results of Yb-doped fibers and Yb-doped bulk glasses by measurements such as electron spin resonance (ESR), X-ray absorption fine-structure (XAFS), and optical transmittance. The results indicate that the formation of Al-oxygen hole center (OHC) by the incidence of pump light is the prime cause of the photodarkening loss.
Highly Environmental-resistant Fusion Splicer
Recently, the installation works of optical fiber cable are shifting from developed countries to BRICs and developing countries where the environment for such works is harsh and the infrastructure is not so advanced. As a result, the market requires a fusion splicer that can maintain high performance even in harsh environment. To meet this market requirement, we have developed a new fusion splicer FSM-60 series.
Field Installable Optical Connector for Cables
With the rapid expansion of fiber to the home (FTTH) in Japan, mechanical splices and field-installable optical connectors have become important components widely deployed in a FTTH network. To date, we have developed and commercialized these components for various fibers as well as drop cables. Applying this technology and expertise, we have developed a new field-installable optical connector for cables. This connector exhibits excellent optical characteristics and reliability tests results. We have designed a low cost jig also to improve the ease of installation.
New Design of Optical Fiber Cable for Easy Mid-span Access
We have developed a new optical fiber cable for access network. The cable is designed to achieve the easier mid-span access as well as smaller diameter and light weight. In order to enhance these characteristics,
the cable has the following features:
+Straight C-slotted rod
+Non-concentric sheath
+Design of strength member
+Dry structure
The cable is optimized with consideration of low temperature characteristics. For evaluation of the cable, the mid-span access time is compared with conventional access cables. We verified that the C-slotted core cable has good workability for mid-span access. In this paper, we describe the design concept and design parameters for minimizing the cable diameter. Moreover, we demonstrate not only that the trial cable has good mechanical characteristics and attenuation properties, but also that the mid-span access work is achieved about 2 minutes, which is 50 % shorter time than SZ-slotted core cables.
New Chip Mounting Technology on Membrane
The membrane used for circuit boards in operation switches is getting smaller due to the miniaturization of digital home appliances. Accordingly, the chip mounting area is required to be smaller. The chip mounting technique currently used for the membrane uses the encapsulation resin to increase bonding strength, but this has obstructed the reduction of the mounting space. To satisfy downsizing requirements, a mounting method in which encapsulation resin is not used has been developed. We have applied this technology, and mass production has been launched.
Long-Range Human-Body-Sensing Modules with Capacitive Sensor
Our company has been developing automotive capacitive sensor modules to sense human body proximity or contact. Our recent study aiming at increased accuracy achieved 2 fF or better capacitance sensing accuracy, making it possible to detect a human body 300 mm away, a distance longer than that possible with existing capacitive sensors. In addition, the sensor electrode structure used in a vehicle cabin was optimized to increase noise resistance and directivity. Furthermore, we made a prototype sensor module and assessed its sensitivity in the vehicle cabin, with the finding that the prototype module is able to sense a hand at a distance of 300 mm or more from the sensor electrode.
Epitaxial Growth of Zinc Oxide for Ultraviolet Light-Emitting Devices
We achieved a high temperature growth of Zn-polar ZnO homoepitaxial film using a high power laser diode module and a novel structure zinc-ionizer. The film grown at 850 °C showed an island structure, which consisted of steps and terraces with a monolayer step-height of 0.26 nm. The full width at half maximum (FWHM) values of X-ray rocking curve (XRC) for ZnO (0002) and ZnO (1012) were 30.9 arcsec and 53.9 arcsec, respectively. The high temperature growth of ZnO homoepitaxial film is an excellent method to improve its surface morphology and its crystalline quality.
Single Crystal Growth of Aluminum Nitride
Single crystalline aluminum nitride (AlN) is a promising material used as a substrate for the purpose of improving the performance of AlN-based III-nitride semiconductors that are expected to be used in high power, RF electronic devices and deep UV LEDs/LDs. Sublimation method with open-system crucibles was chosen for single crystal growth of AlN because open-system growth is helpful in understanding the effects of parameters on crystal growth and has the extended degree of freedom in the selection of growth conditions. As a result of the crystal growth, millimeter-sized AlN single crystals with a dislocation density less than 107 cm-2 were grown on SiC substrates.
RE123 Coated Conductors
RE123 superconductor is known to exhibit superconductivity at the temperature of liquid nitrogen (77 K) and also to have excellent current property in magnetic fields. Therefore, it is expected to be used for various electric applications, so R&D of the wire using RE123 superconductor is now actively promoted all over the world. We have been adopting and developing the wire of thin film type with crystal grain highly aligned in-plane, the so called RE123 coated conductor. We introduced the large apparatus and made all improvements on each process, resulting in successful fabrication of the long wire of 500 m-length with critical current of over 300 A at the rate of over 5 m / h in February 2008. It showed world record performance and reached practical level.
Highly Durable Dye-sensitized Solar Cells
Dye-sensitized solar cell is expected to be one of the next-generation photovoltaics because of its low-cost and environment-friendly properties. Although we have developed some technologies and materials aiming to enhance its practical utility, the cell does not have sufficient reliability for out-door applications so far. The present study investigates newly developed robust solar cells with a novel protection layer of metal circuit and tightly sealed package. The resulting cells showed extremely high stability to pass several endurance tests standardized in JIS for stability of solar submodules, including an endurance test under the heat and humidity environment (85 °C, 85 % RH, 1000 h).
Determination of Alcohol by Partition Chromatography Using an Indirect Electrical Conduction Detector
The partition chromatography method of electrochemical detection is the commonly used method for quantitative analysis of alcohol. In the present, the standard detectors of high-performance liquid chromatography and ion chromatography are ultraviolet-visible detector, differential refractive index detector, and electrical conduction detector. Therefore, we need to prepare new detectors for the analysis of alcohol. We examined the quantitative analysis of alcohol by the partition chromatography method of indirect electrical conduction detection, that based on the phenomenon of alcohol's signal appearing as a negative peak while using the electrical conduction detector of ion chromatography. The calibration curve obtained by using this method is a straight line whose coefficient of correlation was 0.9967-0.9999 in the range of 0.5 mg/L-100 %, thus allowing us to analyze alcohol in a very wide range. In addition, it was found that we could also analyze organic acid and saccharide by the same method.
Ultra-Small Absolute Pressure Sensor Using WLP
Recently, as the miniaturization and weight saving of the information appliances such as cellular phones are getting advanced, the further miniaturization of electronic devices such as ICs and MEMS sensors has come to be demanded. Especially, attention is paid to the application of small pressure sensor for portable appliances, which can measure the atmospheric pressure. We have developed the ultra small absolute pressure sensor applying the wafer level package (WLP) technology to satisfy market needs. The sensor chip has the unique sealed reference cavity, which is formed inside Si chip, so the chip can be made in very small size. In this report, the feature and the characteristics of the WLP ultra small absolute pressure sensor are described.