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  4. No.39 January,2010
Fujikura Technical Review

No.39 January,2010



High-Efficiency Linearly Polarized Fiber Laser
Recently, high-power visible light sources by frequency doubling have attracted great interest in display and medical applications. In order to realize these light sources, linearly polarized light sources that have high output power, high energy-conversion efficiency, narrow spectral width and high polarization extinction ratio are required. We have studied a linearly polarized fiber laser for frequency doubling. We evaluated the characteristics of the prototype and confirmed that it was suitable for frequency doubling.
Ultra-Fast Automatic Gain Controlled Optical Fiber Amplifier
With the growth of photonic networks, high-speed automatic gain controlled optical fiber amplifiers (AGC-EDFAs) are required to suppress dynamic gain transients caused by the rapid change in input power level to an EDFA. We developed the AGC-EDFA using high-speed VOA and measured its transient performance in a 40 channel add/drop operation. Owing to its high-speed response, good transient suppressions as the settling time of less than 3 μs and the gain excursion of less than 0.8 dB for the adding condition and 20 μs and 1.2 dB for the dropping condition were obtained.
Bend-insensitive Optical Fiber: FutureGuide®-BIS-B
We have developed a bend-insensitive optical fiber with a trench index profile, which is called FutureGuide®-BIS-B. The bending losses at bending radius of 7.5 mm of the fiber are compliant with ITU-T G.657.B and are one-tenth as large as that of a single-mode optical fiber employing a step index profile with the same MFD as the bend-insensitive fiber. Since the MFD of the fiber is compliant with G.652.D, the splice loss with the conventional single-mode fiber is low enough for practical use. FutureGuide®-BIS-B is expected to be widely used in access networks, in which the conventional single-mode fiber is used.
Fiber-Optic Strain Sensor with a Millimeter Class High Spatial Resolution
Strain measurements of the 6 m scale composite wing structure were demonstrated by means of optical frequency domain reflectometry (OFDR) using fiber Bragg grating (FBG) sensors. Local strain distribution in the wing was successfully measured with a high spatial resolution of 0.6 mm along the 500 mm length FBG sensor. Overall deformation of the wing was also measured over a 4 m span using the 42-point multiplexed FBG sensor. As the validity of these measured strains was confirmed, the success of the strain measurement technique was verified.
Small-Diameter 1000-Fiber Optical Cables
In Japan, lack of duct space for optical cable has become a critical problem, especially around the central office. In order to overcome this problem, it would be effective to redesign optical cables with small diameter and high packing density. Therefore, we developed new 1000-fiber cables. The diameters of new cables were reduced by more than 20% compared with that of the conventional 1000-fiber cables. As a result, three 1000-fiber cables can be installed in a duct (inner diameter φ75mm) that is usually capable of accommodating only two conventional 1000-fiber cables.
Automated Fusion Splicing of Circular and D-shaped Fiber with Elliptical Core
A new method for splicing D-shaped and circular shaped PM fiber with elliptical core using an automated fusion splicer is described. A Fujikura FSM-45PM splicer is used with new alignment techniques developed for achieving consistent splice loss less than 0.5 dB and Polarization Extinction Ratio greater than 25 dB. This process has been implemented into a commercial product and sold in the fiber market.
Light Guide Film for Mobile Phone
Recently, thin LGF that illuminates mobile phone keys uniformly has been attracting attention. We have succeeded in developing and commercializing it. Base films with high optical transparency and flexibility and ink that diffuses light effectively and possesses high durability are used for LGFs. We established the important technologies of optical simulation and evaluation of brightness. We report the development of these fundamental technologies and introduce the variations of products developed on the basis of the technology.
An Investigation of Differential Impedance Controlled Flexible Printed Circuit
When flexible printed circuit (FPC) is used for a high-frequency signal transmission, it is necessary to adjust the impedance. Moreover, a lot of differential signal transmission methods are adopted for high-speed signal transmission. Therefore, FPC needs the design of the differential signal line. However, it is difficult to design the differential signal line with relatively many design parameters compared with the single-end signal line. This time, our company has installed a three-dimensional electromagnetic field simulator to address this problem. The purpose of this paper is to report that the actual measurement value of FPC designed with the simulator was in good agreement with the result of the simulation.
Fine-pitch and High-density Printed Circuit Board
Recently, the demand for high-density printed circuit boards has risen along with the trend of lighter, thinner, and smaller electronic equipment and the mounting parts and that of an increase in the number of multi pins of ICs. Therefore, we established a fine wiring formation technology and a filling plating technology for fine through holes and developed ultra-high-density double-sided printed circuit boards called μ through hole double-sided flexible printed circuit (FPC). We report on the features and technological development of μ through hole double-sided FPCs.
Piezo Fan for Thermal Management of Electronics
In order to satisfy the demand for light-weight, low power consumption, and compact-sized personal computers, portable electronics, LED applied products and audio electronics, we have developed a 'piezo fan' that works on a different principle from that of motor fans. By using the finite-element method for design support, the demands for long life and compact size were achieved. Also, on the basis of the supposed application, the cooling effects and the cooling possibilities of piezo fans were confirmed by applying them to the heat sources of personal computers, portable electronics, and LED applications.
Small DMFC for Portable Applications
Consumers' demand for commercial portable electronics such as laptop computers, digital cameras, PDAs and cell phones has driven the development of advanced portable power technologies in recent years. Direct methanol fuel cell (DMFC), with benefits such as high energy efficiency, quick start capability and instantaneous refueling, is a promising candidate for portable applications. A 10 W DMFC system has been developed at Fujikura. The system generates the 20 W peak power with external dimensions of 100 x 100 x 170 mm. Recent progress in the development of the small DMFC prototype is reported with emphasis on the fuel delivery subsystem and the gas/liquid separator.
Membrane Circuit Connector
We are considering automotive modules using membrane circuits to meet demands for reduction in size, weight and cost. Membranes are used for sensors and switch electrodes because their manufacturing process is simple and the cost of their materials is low. However, the miniaturization of connectors and the coexistence of a smaller pitch and a multi-face connection have been major challenges in the development of membrane circuits. We have developed a membrane circuit connector that is compatible with an automotive standard-type connector and achieved a multi-face connection.
Heat-resistant (UL90°C) Thin-Foamed Insulator for the Transmission Cable
Further improvement in the transmission properties of the transmission cable in high-frequency region has become necessary. In addition, for the transmission cable, the improvements that the insulator should be thinner and the heat-resistant property should be progressed are also required strongly. To achieve good transmission properties, it is important to improve the performance of the insulator. Therefore, materials of low dielectric constant and low dielectric loss tangent are used, and the insulator is foamed. In order to get the finer cable, a thinner foamed insulator is required. But the problem with the thinner foamed insulator is that it is easily crushed. Consequently, we have developed the heat-resistant (UL90°C) thin foamed crush-proof insulator made by using a new material having good dielectric properties.
High-rate and Long-length IBAD Layers for GdBa2Cu3O7-x Superconducting Film
A large-scale IBAD system with the world's largest ion source was employed to fabricate IBAD-MgO film. We successfully fabricated a 1 km-length IBAD-MgO film at a production rate of 1 km/h. We also studied PLD-CeO2 films directly on IBAD-MgO films. From an observation by TEM of the interface between MgO and CeO2 films, it is revealed that CeO2 film has fine-textured structure on IBAD-MgO though lattice mismatch is large (28.5%). Using the CeO2/MgO substrate, we fabricated PLD- GdBa2Cu3O7-x (GdBCO) film and obtained a high-performance superconducting film whose Ic and Jc were over 300 A and 3 MA/cm2, respectively, at 77 K, self-field.
Highly Sensitive Magnetic Field Sensor Utilizing Magneto Impedance Effect
We report experimental results of a thin film MI sensor integrated with a thin film permanent magnet for generating a bias field. We found that a magnetic field from the thin film magnet works as bias magnetic field and that the sensor possessed a sensitivity around zero magnetic fields. In addition, we found that the magnitude of the bias field depended on the magnetizing direction of the permanent magnet. It was demonstrated that the bias field was adjustable even after fabrication of the sensor element by controlling the magnetizing direction.