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R & D Review

No.101

No.101 April 2004

Photonic Crystal Fibers(2)- Nonlinear Properties and Applications -

A photonic crystal fiber has an array of air holes in the silica glass. The cladding, having a structure made of silica and air holes enable characteristics that are quite different from those of conventional fibers. A photonic crystal fiber has very interesting new features including endlessly-singlemode operation, high nonlinearity, wide range of dispersion management and high polarization maintaining property that results from the very high relative refractive index between the fiber core and air holed cladding.
In this paper, we describe nonlinear properties of photonic crystal fibers and also report the reliability of photonic crystal fiber, which is very important for applications. Furthermore, we report various applications of the photonic crystal fiber technology that have achieved practical use such as the supercontinuum light source.
[Key words] Photonic crystal fiber, Nonlinearity, Supercontinuum, Connectorized patchcord, Reliability

Development of Plug-in Type Optical Fiber Amplifiers with SNMP for FTTH

Recently, demand for FTTH is growing day by day. The required transfer speed has exceeded the limit of electrical transfer, and we are now in the era of optical transmission. FTTH is not only used for data transmission but also for CATV transmission. The Video signals are transferred by optical signals all over the system by optical CATV.
We have developed and manufactured a new optical fiber amplifier as a repeater or distribution adapted for FTTH. It is applicable for both data transmission that requires high gain and high output power, and video transmission that requires high output power and low noise. Moreover this optical fiber amplifier is applicable to the SNMP for network management.
The optical fiber amplifier is the EIA standard 5 U size unit, which can be mounted on a 19-inch rack. It holds up to eight units of optical fiber amplifier, a communication unit, a double power unit, and a fan unit for cooling. All front access is realized. All units and all connectors can be distributed from the front side. This optical fiber amplifier is suitable for the multi repetition system of optical CATV because of its low noise; the noise figure is under 6.5 dB at + 8 dBm optical input.
[Key words] Optical fiber amplifier, EDFA, FTTH, CATV, SNMP, Front access

3D Expanded Fluororesin Foam Dielectric Coaxial Cable

In recent years, along with the rapid spread of mobile telecommunications, base antennas are not only installed in towers built exclusively for antennas, but also on roof tops of private buildings where installation conditions are severe. Therefore, demand is growing for small size coaxial cables that can be used as supply lines to the antenna or as jumpers between equipments.
Small size and low attenuation are the outstanding characteristics of our expanded fluororesin foam dielectric coaxial cable "3D-SUNFLEX coaxial cable". Dielectric material with low loss was selected from thermoplastic fluororesin and the high expansion extruder was used. We also decided to use annularly corrugated outer conductors.
Because of its excellent flexibility and thermal performance, our cable can be used in both public welfare and munition apparatus.
[Key words] Expanded fluororesin foam, Coaxial cable, Small size, Flexibility

A Study of Adhesion of UV-Curable Resin

In recent optical fiber cables for communications, ribbon type optical fiber units of multilayered structure are often employed that use UV curable resins between each layer. It is very important that the adhesion between each layer is controlled as the adhesion has a large influence on the long term reliability of the optical fiber, efficiency during splicing operations and handleability during manufacturing processes.
In this paper we introduce the SAICAS (Surface and Interfacial Cutting Analysis System) method as a method to measure adhesion in ribbon type optical fiber units. We confirmed that the adhesion of the joining layers and the ribbon layers could be evaluated handily, quantitatively and also with good reproducibility. We found the method to be very effective in controlling the processing conditions and the quality of ribbon type optical fiber units.
[Key words] Optical fiber,UV curable resin,Optical fiber units,Adhesion,Handleability, SAICAS (Surface and Interfacial Cutting Analysis System)

Development of Double Cladding Fiber Lasers

Double Cladding Fiber Lasers, a kind of rare-earth doped high performance fiber laser, are designed to use high- power multi-mode laser diodes as a pumping light source. By pumping Nd3+ or Yb3+ ions in the core glass, high power 1 µm-band laser light is obtained effectively. Single-mode, multi-mode, and even polarized single-mode beams are available according to core parameter design. These new type lasers are easier to manipulate than the conventional types of lasers because the beam launches from the small core of double cladding fiber lasers.
We developed Air-hole type double cladding fiber lasers by applying photonic crystal fiber manufacturing technique. Air-hole claddings surrounding a pumping guide enable them to be excellent fiber lasers with high NA and high reliability. Optical power conversion efficiency of 63% was obtained from our Yb-doped double cladding fiber laser. There are plans to use them for light sources and in welding usages.
[Key words] Fiber lasers, Double cladding, Laser diode pumping, Air-hole

Development of Blue SHG Device

Development on shorter wavelength laser light source for next generation displays or high-density DVD recorders has been the latest and hottest topic at many R&D centers in the world. One of the technologies to realize a short wavelength light source is SHG (Second Harmonic Generation) from longer wavelength lasers using non-linear optical crystals.
In this paper, we report on a high efficient waveguide Blue SHG device based on Periodically Poled Magnesium Oxide doped Lithium Niobate (PPMgLN).
MgO doped LN crystal has good endurance against photo-refractive damage, and PPMgLN shows high conversion performances without heating the crystal.
Periodically poled structure were fabricated from such MgO doped LN crystal, then optical waveguides were fabricated on the +z surface by proton exchange process to yield higher conversion efficiency. Dimensions of the device is 10 mmL × 5 mmW × 0.3 mmt. Poled domain grating period is 4.6 micrometers and the domain duty cycle is 46.9%.
Using a 940 nm semiconductor laser of 30 mW as an incident light source, we confirmed blue light emission of 1.03 mW as the converted second harmonic light from the other end of the device at room temperature. Normalized conversion efficiency was 114.0%/ Wcm2
[Key words] Blue SHG, PPLN,PPMgLN,QPM,Quasi- Phase Matching, SHG, Second Harmonic Generation, Short wavelength,Optical waveguide

Development of Waveguide SFG Device

Quasi-Phase Matching (QPM) method has been widely implemented in search of novel light sources, which are difficult to realize by conventional technology.
So far we have developed Optical parametric oscillators that have more than 60W average output power, C-L band conversion devices using difference frequency generation, and blue and green second harmonic generation devices. In this paper, we report on the high efficient waveguide SFG (Sum Frequency Generation) device based on Periodically Poled Magnesium Oxide doped Lithium Niobate (PPMgLN).
MgO doped LN crystal has good endurance against photo-refractive damage compared to non-MgO doped LN crystal, and the waveguide PPMgLN shows better conversion performances than bulk LN crystals. Dimensions of the SFG device is 10 mmL × 5 mmW × 0.5 mmt. Poled domain grating period is 19.9 micrometers; the waveguide is fabricated on +z surface.
Using 1530 nm semiconductor laser as a signal light source and 1600 nm band tunable laser as a sampling light source, we measured the sum frequency generation at around 788 nm. Normalized conversion efficiency was 67.9%/W. This figure shows improvement by more than three orders compared to conventional experiments using bulk crystals. Measurements were carried out at 25 degree Celsius. No fluctuation of output power was observed.
[Key words] Quasi-Phase Matching, PPMgLN, Sum Frequency Generation (SFG), Optical waveguide, Optical communication

Micro-Machining Using 10 kW High Peak Power Fiber Pulse Laser

We report on MITSUBISHI CABLE’s high peak power fiber pulse laser, LP155R-10kW. The laser consists of a two- stage erbium doped fiber amplifier (EDFA) designed for pulse amplification. The output of this fiber laser is 1.55 µm, has a transversal single mode laser beam and its peak power and pulse width of FWHM is approximately 10 kW and 2 ns respectively. The high peak power and pulse of nano seconds in this system makes it possible to reduce time for machining. As a result, little damage occurs around the processed regions. The output transversal single mode laser beam can be converged to diameters of minimum theoretical diffraction, allowing high beam densities on the specimens to be adjusted to more than 10 GW/cm2. Furthermore, the transversal single mode beam can micro-fabricate with little non-circularly error. As a result, we found this fiber laser system to be suitable for precise micro-machining.
In this report, thin metal and crystal plates were micro-machined by micro-drilling and micro-scribing. The micro- structures of the processed specimens were observed by a scanning electron microscope and an optical micro scope. As it is well known, it is difficult to process hard and brittle material as tungsten and Diamond-Like-Carbon (DLC) coating using normal cutting tools. However, using this fiber laser, it can micro-drill into these samples without making cracks and dross, and without melted adhesion around the processed portions. Dull fabrication and micro- scribing are also examined on SUS304 sheets. The process behavior is considered through observations of the microstructures of these processed specimens, and the reason for the dross suppression in this laser system is discussed. Furthermore, by increasing the beam densities to 80 GW/cm2 using Φ4 µm converged lense, we found that crystals such as sapphire and lithium niobate could also be micro-scribed.
[Key words] Micro-machining, Micro-drilling, Micro-scribing, Dull, Fiber pulse laser, Tungsten, Diamond-like-carbon, Sapphire, LiNbO3

Development of Automotive Network Components

We have developed an automotive optical connector and a media converter based on the automotive optical network standard "IDB-1394". The "IDB-1394" is a modification of the multimedia network standard "IEEE-1394" that provides infrastructure for multimedia devices in the vehicle. A plastic optical fiber (POF) is used for transmission to realize high-speed communication exceeding 100Mbps and to satisfy EMC (Electro Magnetic Compatibility). Automotive optical connectors satisfy the severe environmental test standard for automobiles. Our optical connector has satisfied the "IDB-1394" standard in both optical and mechanical characteristics. A media converter is used to convert "IEEE-1394" electrical signals to "IDB-1394" optical signals. The IDB-1394 demonstration system was exhibited in the 37th Tokyo motor show where we demonstrated data transmission of motion pictures such as DVDs.
[Key words] Optical Connector, POF, IEEE1394, IDB-1394, MOST, Hot Bond, Media Converter

Development of New Sealed Connectors

In the trend of advance of car electronics required for additional application of electronic requirements, wire- harness volume has been increasingly enlarged. Within automobile wire-harness, most crucial component is apparently connectors and their required quantity becomes more and more. However wire-harness is still a labor-intensive product and therefore handling of connectors plays an important role in its quality and performance. Keeping up with the progress of car electronics, it is essentially required to achieve possible reduction in environmental issues as a result of decrease in power consumption by way of further miniaturization and lighter weight of connectors, based on application of smaller size of wires.
For such problems as its handling and electrically stable contact function in case of adoption of further miniaturization and lighter weight of connectors, it is absolutely expected to consider substantial countermeasures.
On the other hand, it has been occurred in case of wire-harness being installed without protection that there have been occurred crack and/or separation of wire covering at the time of car washing using highly pressurized water, resulted in the problem of ingress of water into the connector and subsequently occurrence of electrical contact failure. Moreover, it has been reported that the same problems have been also happened by bite of small animal.
In comparison with the conventional type of connectors, our newly developed "Sealed Connector" has much improved design constitution composed of the front holder to be pre-set in the connector and the rear protector possibly to be equipped optionally, bringing success in achieving labor-saving and easy maintenance. It goes without saying that our newly developed connector is remarkably effective against possible contact failure caused by ingress of water(, resulted from popularization of the highly pressurized water washing machine for cars) into the connector.
[Key words] Connector, Wire-harness, Front holder, Weight reduction and compact designing, Maintenance, Highly pressurized water washing, Small animal

Development of Transparent Wave Absorbers for ETC Systems

ETC lanes in highway toll gates are expected to increase as the number of vehicles using ETC increases. To avoid the influence of unnecessary waves on the adjacent lane, transparent wave absorbers that have both see-through and lighting effects are required between lanes. We developed a transparent wave absorber for ETC based on a new design concept.
In this report we introduce the design concept, characteristics and construction examples at highway toll gates.
[Key words] ETC, Transparent wave absorber, Urban highway, All light transmittances

Effect on Tribological Behavior by Filler Mixed in Polytetrafluoroethylene Composites

Generally, polytetrafluoroethylene that is filled with various materials is used as material for dynamic seals for their excellent properties, such as low dynamic coefficient of friction, high thermal stability, and chemical resistance. As equipments recently tend to be operated under high pressure and high speed, long term stable control and low torque under severe conditions are required. Therefore seal materials that have long term stable friction and wear resistance are necessary.
This report shows the influence of the filler mixed in polytetrafluoroethylene composites on tribological behavior under high pressure, high speed and high temperature. The result of this study shows that it was possible to classify polytetrafluoroethylene composites into three groups according to coefficient of friction behavior. It was clear that each group had its individual merits. We found out that new material that was designed by combining the profiles of three groups can satisfy the requirements of stable friction for long term and wear resistance under severe conditions.
[Key words] Polytetrafluoroethylene, Filler, Coefficient of friction, Wear resistant, High temperature, High pressure

Developments of Thermoplastic Rollers and Trials of New Mold Systems

Our thermoplastic rollers that are made by technique from cable extrusion have been used in automatic photo- printers and OA machines for several years. In this paper, we introduce rollers designed especially for a new dental X-Ray processor.
Moreover, a new mold system was tried instead of extrusion. To meet recent market demand for longer length rollers, the authors first manufactured rollers by the extrusion method. However, the extrusion method, which has excellent accuracy and length capability, is costly. There is also the injection method, which is low cost but unfortunately poor in accuracy and length capability. As the result of comparing both mold systems and analyzing injection system in detail, we developed a new mold system that has good accuracy, length capability and also good cost performance. The products manufactured by the new system will be global standard in the field of photo-printer, OA machines and X-Ray processors.
[Key words] Thermoplastic roller, Thermoplastic resin, Metal core, Extrusion mold, Injection mold, Thermoplastic elastomer, X-Ray processor

On-site Insulation Diagnosis of XLPE Cables Using the Residual Charge Method

The authors paid attention to the superior, "Residual charge method" as an insulation diagnostic technique for over 22 kV XLPE cable lines, and have improved the technique for on-site diagnosis. Based on the knowledge from the improvements, we have manufactured an on-site diagnosis system for over 22 kV XLPE cable lines.
This system can be applied to approximately 5 km of 22-66 kV class XLPE cable lines. It is constructed into a 3 t vehicle which is capable of small sharp turns. Preparations required on site are, to settle cable ends and to extend and connect lead cables and power supply cables. It can provide highly sensitive measurement even under environments such as EMC or stray DC current noise. This system has been in use for on-site diagnosis since December 2002.
[Key words] Water tree, Deterioration diagnosis, XLPE cable, Residual charge, On-site diagnosis

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