No abstract

We have succeeded in observing sprites for winter lightning in the Hokuriku area (Japan Sea side) of Japan in the winter of 2001/2002. The optical results on three days are compared with the corresponding characteristics of parent (causative) lightning with particular attention to the significant diferences between Hokuriku winter lightning and the more widely studied continental lightning. Despite significant differences with Hokuriku winter lightning. We have found nearly the same sprite properties as already observed in the US. continent with a signiJicant difference (simpler shape for Hokuriku winter sprite). Then, we have also discussed the criteria for sprite occurrence. Specifically, two similar criteria are found: ( I ) cloud-to-ground discharges of positive polarity and (2) the presence of a certain threshold in vertical charge moment(2000-300C km) (roughly consistent with that for the U.S. continent ). Mesoscale convective systems are not necessary to store the charge necessaly for sprites, but the parent Hokuriku winter clouds are substantia& smaller than the minimum scale for sprite occurrence in the continental lightning, but it is larger in area than ordinaly summer thunderclouds. However, there may exit another condition such as clustering or self-organizing effect of thunderclouds for sprite production.

This paper reports a hybrid integrated light source fabricated on a Si platform using a spot-size converter (SSC) with a trident Si waveguide. Low-loss coupling for 1.55 μm and 1.3 μm wavelengths was achieved with merely the simple planar form of a Si waveguide with no use of complicated structures such as vertical tapers or an extra dielectric core overlaid on the waveguide. The coupling loss tolerance up to a 1 dB loss increase was larger than the accuracy of our passive alignment technology. The coupling efficiency was quite robust against manufacturing variations in the waveguide width compared with that of a conventional SSC with an inverse taper waveguide. A multi-channel light source with highly uniform output power and a high-temperature light source were fabricated with a 1.55 μm quantum well laser and a 1.3 μm quantum dot laser, respectively. The integration scheme we report can be used to fabricate light sources for high-density, multi-channel Si optical interposers.

Engineers are currently facing some technical issues in support of the exponential performance growths in information industries. One of the most serious issues is a bottleneck of inter-chip interconnects. We propose a new "Photonics-Electronics Convergence System" concept. High density optical interconnects integrated with a 13-channel arrayed laser diode, silicon optical modulators, germanium photodetectors, and silicon optical waveguides on single silicon substrate were demonstrated for the first time using this system. A 5-Gbps error free data transmission and a 3.5-Tbps/cm(2) transmission density were achieved. We believe that this technology will solve the bandwidth bottleneck problem among LSI chips in the future.