Toshikazu Shibata

The dispersion-free filters for DWDM systems using 30 mm long symmetric fiber Bragg gratings

The dispersion-free FBG is designed by applying the optimized cosine-progression to the apodization profile. As experimental results show that it offers the suitable filter, with 25 dB crosstalk, 15 ps group delay, for high bit-rate DWDM systems.

Development of 3-Phase 1kA Class High Tc Superconducting Power Cable Prototype

A 3-phase HTSC(Bi-2223 silver sheathed) cable prototype[1] was developed. This prototype consists of three cable cores housed together in a thermally insulated pipe. Each cable core has a magnetic shield made with HTSC. The electrical performance of this prototype has been evaluated at 77K with 3-phase transport currents. The measurement of AC losses and inductance show that the dominant loss due to current loading is hysteretic loss, and that magnetic shields confine self magnetic fields within each cable core, and avoid inducing the eddy current loss in the thermally insulated pipe. The total current loading loss at 3-phase 1kA operation was 3.5W/m • cct.

A temperature-insensitive erbium-doped fiber amplifier for terrestrial wavelength-division-multiplexing systems

We have evaluated a variation in the temperature dependence of an erbium-doped fiber gain spectrum by a pump wavelength in the 980-nm band for the first time. By optimizing both the pump wavelength in the 980-nm band and a temperature-sensitive gain flattening filter, the gain change of an erbium-doped fiber amplifier was successfully suppressed to 0.18 dB/sub pp/ in the temperature range between 0/spl deg/C and 65/spl deg/C and the wavelength range of 37.0 nm.

Development of HTS cable Conductor with Multi-layer Structure

Alloy-sheathed Bi2223 multi-filamentary tape was developed for the application of high Tc superconducting (HTS) cable. We investigated the mechanical properties of alloy sheathed tape and designed HTS cable conductor with multi-layer structure. The pitch in new designed HTS cable conductor was determined for the purpose of suppressing the unbalanced current distribution in ac current loading. The conductor with alloysheathed tapes which is high tolerance for the mechanical strain has advantage of the current capacity in this design.

Initial Loading Test of 30m Long High Tc Superconducting Power Cable Prototype

A 30m long 66kV-lkA high-Tc superconducting prototype cable system was developed. This system consists of a single phase cable (made with cable manufacturing machines with some additional improvement), terminations, a 66kV XLPE cable for current loop, and a closed cycle liquid nitrogen cooling system. After cooled down, loading tests was performed. The Ic of this cable is 1600A(over the peak value of AClkA). AC40kV-lkA was successfully applied in sub-cooled liquid nitrogen (72K,1.2kg/cm2 bs) regardless of mechanical history, such as handling in the factory, transportation, laying, and the axial force due to contraction during cool down.

Implementation of 2000A Class High-Tc Current Leads for the Superconducting Compact SR Ring “NIJI-III”

We implemented the 2000A class current leads using the High-Tc superconductor for our superconducting compact SR ring “NIJI-III” built in our Harima Laboratory. They are composed of the part of copper at the temperature above 77K and the part of silver-sheathed High-Tc superconducting tape below 77K. In order to reduce the heat leak, a larger number of the High-Tc tapes are stacked for the higher temperature part and a fewer number of them are used for the lower temperature part. We measured the heat leak of these current leads operating at 2000A and obtained the result that the heat leak is 0.7 W/lead. This value corresponds to 1/3 of the heat leak of the conventional copper leads. We installed these current leads and developed a lead monitoring system for “NIJI-III ”. These current leads are now under operation for a year.

Development of 2kA-Class High-Tc Superconducting Current Lead

We made and practically used 350A current lead for SMES magnet, and developed the lead into a large current carrying lead. The leads were made by stacking the Bi-based silver-sheathed wires thick in a high temperature region and thin in a low temperature region to reduce the heat conduction through the silver sheath. They were fixed on a FRP by a resin to improve the mechanical properties. The overall Jc at 77K was about 5,000–6,000A/cm 2 showing that the compactness can be achieved. The heat leak was 0.14W/lead when the lead carried 500A. For a large current carrying lead, 4 units were connected in parallel to increase the current capacity. The heat leak of the large current carrying lead was 0.345–0.412W/(kA•lead) when the lead carried 2.5kA. This proves that the high-Tc current leads using the Bi-2223 silver-sheathed wire are available even for a large current carrying lead, and has low heat leak property.

Amplified coarse WDM system employing uncooled fiber Bragg grating lasers with 600 GHz channel spacing

We propose a cost-effective 8-channel coarse WDM system employing uncooled fiber Bragg grating lasers with 600 GHz channel spacing. Gigabit Ethernet transmission experiment using a conventional EDFA supports feasibility of this system even over dispersion-shifted fibers.

10 Gb/s transmission performance of cascaded group-delay-flattened fiber Bragg gratings

For the purpose of applying 10 Gb/s DWDM systems, the group-delay-flattened FBGs, which have both square spectral response and linear phase response, are developed. The conventional FBGs have the large group delay variation in the reflective bandwidth, and the accumulation of the dispersive effects is serious problem in cascading. On the other hand the group-delay-flattened FBGs has linear phase response, and the power penalty in cascaded 5 FBGs is under 0.1 dB independently of wavelength. These results confirm that the group-delay-flattened FBGs reflect the 10 G/s signals keeping the original waveform well. It therefore results that the group-delay-flattened FBGs are suitable for ADM used in 10 Gb/s DWDM optical transmission system, and these FBGs may be ideal devices for more complicated DWDM network systems.