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R & D Review


No.100 April 2003

Development of High Efficiency Waveguided Green 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 the high efficiency waveguided green SHG devices based on Periodically Poled Magnesium Oxide doped Lithium Niobate (PPMgLN).
SHG from periodically poled crystal, generated by Quasi-Phase Matching, is a promising technology, because of the wideband harmonic wavelength ranging from ultraviolet to infrared and high conversion efficiency.
Research on LN as a periodically poled crystal, has been very popular, regardless of such inadequacy as the weakness against photo-refractive damages. Therefore high temperature operation has been must for the LN crystals. On the other hand, MgO doped LN crystal has good endurance against photo-refractive damage, and PPMgLN shows high conversion performances without heating the crystal.
Green SHG devices in this report were manufactured from this MgO doped LN crystal with the optical waveguides fabricated on the +z surface by proton exchange process to attain higher conversion efficiency than the bulk crystals.
Dimensions of the device is 10 mm (L) × 5 mm (W) × 0.3 mm (t). Poled domain grating period is 6.9 micro-meter and domain duty cycle is 56.9%.
Using 1064 nm Nd:YAG laser of 50 mW as an incident light source, we confirmed the strong green light emission of 4.1 mW as the converted second harmonic light from the other end of the device at room temperature.
[Key words] Quasi-Phase Matching (QPM), PPMgLN, Second harmonic generation (SHG), Short wavelength, Optical waveguide

Development of Ultraviolet AlGaN Photodiodes(2)
- Properties of the Responsivity in Vacuum Ultraviolet Region -

As the finer and higher integrated semiconductor technologies progress, the shorter exposure light sources for lithograph to satisfy more demanding requirements have been developed. Nowadays, KrF excimer lasers (5.0 eV,λ= 248 nm) are widely operated in many mass production lines of lithography. Manufacturing lines utilizing ArF excimer lasers (6.5 eV, λ= 193 nm) are also becoming available. As the next generation technology, lithograph systems using F2 lasers (7.9 eV, λ= 157 nm) or Extreme Ultraviolet (EUV 95 eV, λ= 13 nm) as their light source are now being developed at many R&D centers. As for the ultraviolet light photodetector, Si (Silicon) based photodiode sensors have been widely accepted regardless of their insufficiency such as requirement of visible - cut - filters or vulnerability to high energy ultraviolet light exposure. In this report, we introduce AlGaN based photodiode and its responsivity properties in the vacuum ultraviolet region (λ<200 nm). The responsivity measurements were carried out by using synchrotron radiation launched from UVSOR.
As a result, we confirmed ;

  • Photodiodes with comb - shaped electrodes can not detect the light exactly in the region of ≥ 10 eV (λ ≤ 124 nm), because of the photoemission from the device surface.
  • Photodiodes covered with transparent Schottky electrode (Au / Ni) to prevent the photoemission can detect superb wide spectrum of ultraviolet light at 3.5 - 25 eV (λ= 354 - 50 nm).
  • The maximum responsivity of the latter is 0.15 A/W at 3.5 eV (λ= 354 nm).

[Key words] AlGaN,Ultraviolet,Potodetector,Vacuum ultraviolet, Responsivity

Development of Optical Fiber Amplifiers for SNMP-Based Network Management Systems (FA155RN)

In recent years, broadband Internet using xDSL, CATV network, and FTTH as an access system is increasing rapidly by the e-Japan strategy led by the Japanese government and the project for regional intranet. With it, a broadband Metro Network using the GbE (Gigabit Ethernet) technology, which is flexible at low price with a simple solution, will be formed in MAN (Metropolitan Area Network) or SAN (Storage Area Network). It is desirable for the EDFA used in the broadband Metro Network to be managed in the same manner as other Ethernet apparatus.
Therefore, we have developed and manufactured EDFA applicable to SNMP (Simple Network Management Protocol) and Telnet that are a standard network management protocol as TCP/IP network apparatus.
It is the EIA standard 1U size unit which can be mounted on a 19 inch rack with high reliability by rendering a double power supply. It is most suitably designed for practical use, with such functions as Light Emitting Diode display / relay output during alarm, trap transmission by network management when rendering alarm, and a log function.
[Key words] Optical fiber amplifier, EDFA, Er doped optical fiber, EDF, SNMP, Telnet

The Characteristics of WDM Transmission Systems with Add/Drop Nodes Using Low Noise AGC Optical Amplifiers

Photonic-networks are presently in the spot light of optical transmission networks. In a photonic-network, optical fibers are made in a ring or spread in a mesh. In the fiber, WDM (Wavelength Division Multiplexing) signals are transmitted, to the add/drop nodes on the optical route. Part of the WDM signals are dropped in other lines, or added from there. This is how the number of waves in the fiber is changed in a photonic-network with add/drop nodes. Many optical amplifiers are placed to compensate for the fiber loss. The input power to the optical amplifier also changes.
Normally, optical amplifiers are controlled to maintain constant total output power. Therefore the output power of each channel is changed by the fluctuated input power. OAGC (Optical Automatic Gain Control) optical amplifier, which keeps the gain to be constant, is being considered instead of controlling the total output power in order to suppress the fluctuated gain caused by fluctuated input power.
We have developed a new type of AGC optical amplifier called the HAGC (Hybrid Automatic Gain Control), which has low noise figure equal to normal amplifiers by electrical feed-back added to optical feed-back.
We estimated the characteristics of the gain fluctuation and the transmission with add/drop nodes during WDM transmission. We estimated the gain-wavelength characteristics when eight out of sixteen signals were dropped. The gain varies only 0.14 dB MAX, and the gain deviation varies only 0.062 dB MAX. Although the power in the fiber is fluctuated by the signal add/drop in the photonic-network, the output power of each signal is stable by the HAGC optical amplifier.
The transmission characteristics by bit error rate of the HAGC optical amplifier is 0.5 dB better than that of normal optical amplifiers, when half of WDM signals were dropped. Because there are some optical amplifiers in the route, the difference of the characteristics is clear.
Our evaluations of WDM amplified characteristics by HAGC optical amplifiers clearly shows it is useful in photonic- networks with add/drop.
[Key words] Add/Drop, Optical AGC, WDM, Photonic-network, Low noise Figure, Gain deviation

Examination Regarding Wavelength Characteristics of the Wide Band Optical Amplifier Operating in the 1 µm Region

An amplifier for laser light sources of the 1 µm region such as the Nd-YLF (1047, 1053 nm) and the Nd-YAG (1064 nm) used in industrial and optical measuring fields is required. Though characteristics of the amplifier operating in the 1 µm region using Nd-doped fibers have been studied, wavelength characteristics of the gain and the noise figure regarding Yb- doped fibers which also have an amplification range in the 1 µm region have not been studied yet.
By optimizing the YDF parameters such as cutoff wavelength and the Yb concentration, we succeeded in developing a highly efficient Yb-doped fiber amplifier (YDFA) that has a conversion efficiency of 66%. Furthermore, we developed a tunable fiber laser operating in the 1 µm region using YDFs as the amplification medium and used this laser as a signal light source for the YDFA.
As a result of evaluating the wavelength characteristics of the gain and the noise figure of the YDFs, we found that the peak wavelength of the Yb gain exists at around 1030 nm. Small signal gain is over 42 dB, and noise figure is under 5.0 dB.
In addition, YDFAs are maintenance free, constructed entirely of fibers assuring high quality and stability. They can be used not only as an amplifier for lasers of the 1 µm region but also as an oscillator for pulse light sources.
[Key words] 1 µm region, YDFA, Wavelength characteristics, Fiber laser, Low noise figure, Cutoff wavelength, Maintenance free

Development of ITS Technologies (2)

ITS (Intelligent Transport Systems), that solves various problems on road traffic by networking person, vehicle and road, is in steady progress. VICS (Vehicle Information and Communication System) and ETC (Electronic Toll Collection System) are being spread for common use and proving tests on actual roads are being conducted for AHS (Advanced Cruise-Assist Highway Systems) projects.
For this ITS business field, we have been developing technologies classified into three networks systems; wired, wireless, and in-vehicle networks.
We report on the main results and related trends on IP (Internet Protocol) network systems, anti-icing system for roads, electromagnetic wave absorbers, leaky wave guide, ITS data bus, and Inter-vehicle communication systems which were developed by these technologies.
[Key words] ITS, Vehicle, Road, Wired network, Wireless network, Inter-vehicle network

Copper Oval Leaky Waveguides for the 5.8 GHz Frequency Bands

Wireless communication systems which use 5.8 GHz band such as the DSRC (Dedicated Short Range Communication) are developed as communication systems for vehicles and the roadside for the ITS (Intelligent Transport Systems). Beacon antenna and LWG (Leaky Waveguide) methods are examined as the sending and receiving antenna for the roadside of the system. Because LWG has excellent characteristics in which electric waves can be uniformly radiated in extensive communication areas, it is expected to be widely used in vehicle to roadside communications system such as the DSRC.
Our LWG has zigzag and periodically arranged slots on the walls of the waveguide to radiate the electromagnetic field. We have obtained the electric characteristic shown as follows by appropriately designing the slot size and intervals. The results are ; radiation angle for LWG axis : 45° (Direction of backfire), directivity for cross section : ± 49°, coupling loss : 61 dB , attenuation characteristic : 0.076 dB/m.
[Key words] ITS, DSRC, 5.8 GHz band, Leaky Waveguide (LWG), Wireless communication

Corrugated Leaky Coaxial Cables

Low pricing of radio communication systems has extended the use of radio communications. The operating frequency is becoming a microwave band with improvement in the access speed. LCX (Leaky Coaxial Cable) is used as an antenna for transmission and reception in confined areas such as tunnels or underground. However, the characteristic in demand ranges from several MHz to several GHz.
The corrugated LCX (W-LCX:Wideband Leaky Coaxial Cable) has holes for radiating electric waves on external conductors of the conventional corrugated coaxial cable. Therefore, it can be expected to have wideband characteristics by radiation of coupled mode. We experimented with a corrugated LCX to clarify many characteristics.
Compared to the conventional LCX using radiation mode, the corrugated LCX is applicable to wideband use. Furthermore, it excels also in flexibility and economical efficiency. Applications to various radio communications systems can be expected.
[Key words] Wideband, Radio communication, Confined areas, Leaky coaxial cable (LCX), Corrugate, Coupled mode

Development of Low-Loss Materials for Coaxial Cables Used under High Frequency Bands
-The Investigations of Dielectric Characteristics for Insulation Materials of Coaxial Cables by the Cavity Perturbation Method at Ultra High Frequency (GHz) Bands-

According to a spread of communication networks (e.g. cellular phone, cable television), the demand for coaxial cables used under high frequency bands has been increasing .
Furthermore, the new demand for intelligent transport systems (ITS) has been growing rapidly. Coaxial cables are required for being applied in higher frequency and lower transmission loss from such a background.
The cause of loss in coaxial cable used under high frequency bands is related to inner and outer conductors, besides the dielectric loss from insulation materials. However at the giga-hertz band ,we have not been able to measure the dielectric loss of insulation materials directly. We could only measure the whole loss of coaxial cable.
In this paper we introduce a measurement system applying the cavity perturbation method, which enables us to measure the dielectric loss of materials directly, to find the differences of dielectric characteristics against density of polyethylene, heating treatment of polytetrafluoroethylene and the kinds of end groups of tetrafluoroethylene- perfluoroalkylvinylvinylether copolymer. Improvements on the transmission loss of coaxial cables were made.
For faster development of insulation materials for coaxial cables it is necessary to find out which factor influences dielectric characteristics. We are confident that the cavity perturbation method should become very useful.
[Key words] Polyethylene, Polytetrafluoroethylene, Tetrafluoroethylene-perfluoroalkylvinylether copolymer, Giga-hertz, Coaxial cable, Cavity perturbation method, Low-loss, Ε, Tan δ

Development of Heat Resistant UV Transmission Optical Fibers (2)

Recently, Deep Ultraviolet (DUV) light, ex. excimer laser, is used for the semiconductor process. When usual optical fibers for ultra violet region are exposed to DUV light, many defects are induced in the core glass, and transmission loss are increased by these defects. Therefore, these optical fibers cannot be used for the DUV region.
We have developed the excellent DUV transmission and high heat resisting silica core optical fibers by developing a new hydrogen doping technique into aluminum coated optical fibers. The technique keeps high DUV transmission over an extended period of time.
In this paper we describe the mechanism of transmission loss of the optical fibers by DUV irradiation, improvement of DUV resistance by hydrogen, and effect of the heat-treatment to the newly developed optical fiber.
[Key words] Excimer laser, DUV, Optical fiber, Defect, Aluminum, Silica glass, Hydrogen, Ultraviolet radiation resistant

Development of Highly Damage Resistant Anti-Reflection Coating

High power laser is an important tool for industry. MITSUBISHI CABLE INDUSTRIES, LTD. is supplying optical glass fibers for high power lasers. It is very important to supply for the edge face of the optical glass fiber with anti- reflection coating (AR) to reduce reflection loss. However, there is not AR coating for high power laser, further the AR coating is of no practical use.
We have developed a highly resistant AR coating for high power YAG laser of more than 4 kW. In this paper, we studied an AR with a high damage resistance by Taguchi method and laser annealing. This AR coating has a reflectance of for ≤ 0.2% at 1064 nm (Nd:YAG laser) and a damage threshold of 14.7 J/cm2 at 1064 nm (τ=7 ns). It is possible for the AR coating to use YAG laser guide of the 10 kW class.
[Key words] Anti-reflection (AR), YAG laser guide, Ion-assisted deposition (IAD), Damage threshold, Laser annealing

Development of "PRESET HANGER" for Cable Bundling

Recently, rapid service and construction of domestic information-infrastructure is being promoted. On the installation of overhead cables which are indispensable for infrastructure services, various methods, such as usual hanger or spiral hangers had been adopted. Most of these methods force the workers to operate at dangerous heights, and are time consuming.
Under these situations, we have developed "PRESET HANGER" as an unprecedented product for efficient cable installation, reducing the construction cost of facilities, and making use of space effectively with cable bundling.PRESET HANGER is a factory assembled messenger wire with folding hangers. As the hangers are able to rotate around the messenger-wire, it is possible to construct a longer overhead cable- route without intermission by using guide rollers.
As the installation of PRESET HANGER is completed in one-process, it enables drastic reduction of lead time, and also decreases operations at heights. With the usual methods, the following three-processes are enforced separately, installing messenger wire, attaching hangers to the messenger wire, and installing rope into the hangers. PRESET HANGER is also suitable for cable bundling, as it is easy to install the rope into the hangers by using exclusive rope installers.
[Key words] Information-infrastructure, Overhead cable, Cable hangers, PRESET HANGER, Rope installer, Cable bundling, Multi-cable installation

Development of New Metal Seals
- Metal Seals with Low Compression Force -

In recent years, the use of industrial equipment in severe conditions are growing. The seals applied in such conditions must endure high and very low temperatures, various kinds of fluid and gases. In addition, in the semiconductor industry, seals using elastomer or plastic materials cannot endure out gas and gas penetration. Therefore, elastomer or plastic seals are being replaced with metal seals represented by metal-O-rings.
However, it is difficult for engineers to apply metal-O-rings to various equipments, because of their larger compression force, smaller spring back and their tend to damage the flange surface. Therefore, metal seals are used only in limited situations.
We have developed three kinds of new metal seals. These seals are improved to overcome the weak points of metal- O-rings.

  • "SUNLIMES I " ····· Larger spring back, lower compression force, easy to handle than metal-O-rings.
  • "SUNLIMES II " ····· Lowest compression force, high performance for sealing capability without surface treatment (plating and coating), suit to the center-ring application of vacuum seal.
  • "SUNLIMES III " ····· Lower compression force than metal-O-rings, suit to small size seals as semiconductor specification "SEMI 2787.1".

[Key words] Metal seal, Compression force, Spring back, High vacuum, Corrosion resistance

Development of Junctions Module for the Car Wiring System

The recent trend surrounding the car industry is changing to emphasize environmental protection and toward value added multiplexed functional performances. Under these circumstances, wiring systems tend to be larger and more complex with the increase of car electronics.
Carmakers domestic and abroad are deploying competition for survival in an attempt to reduce substantial cost reduction. One of the measures to reduce costs is implementation of modules in car assembling. Modularization is considered in a wide range from small parts such as switches, to parts of the car body such as bumpers.
The biggest theme in the implementation of module is considered as the connection reliability and workability of each module products. We have paid much effort in developing a new wiring system for cockpit modules and as a result, we have succeeded in developing a special junction module implement cockpit modules.
Junction module is designed to achieve automatic connection of the wiring of the cockpit and body by applying the newly developed float-mount connector and a system that consists of a junction block which is the essential part of wiring function and ECU(Electric Control Unit)of the car LAN. At the same time, by applying the newly developed wall-mount connector, we have succeeded in relinquishing hole wiring which is considered as one of the biggest problems at the time of dismantling wire harnesses.
We will introduce a new wiring system where the new junction module is applied.
[Key words] Wire harness, Module, Float-mount connector, Wall-mount connector, Water-proof

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