Kentaro Kobayashi

On-chip optical interconnection by using integrated III-V laser diode and photodetector with silicon waveguide

On-chip integration of III-V laser diodes and photodetectors with silicon nanowire waveguides is demonstrated. Through flip-chip bonding of GaInNAs/GaAs laser diodes directly onto the silicon substrate, efficient heat dissipation was realized and characteristic temperatures as high as 132K were achieved. Spot-size converters for the laser-to-waveguide coupling were used, with efficiencies greater than 60%. The photodetectors were fabricated by bonding of InGaAs/InP wafers directly to silicon waveguides and formation of metal-semiconductor-metal structures, giving responsivities as high as 0.74 A/W. Both laser diode and the photodetector were integrated with a single silicon waveguide to demonstrate a complete on-chip optical transmission link.

Development of 765kV transformer protection relay

Currently, ultra-high-voltage (UHV) systems are under development in many countries around the world in order to accommodate the increasing levels in demand for electric power. In Korea, the commercialization of a 765kV ultra-high-voltage system has been ongoing since 2002. We have developed a number of protection relays suitable for the UHV system to enable us to make a contribution to the 765kV UHV projects in Korea. During the development of the protection relays for the 765kV UHV system we encountered several technical issues of particular interest in relation to the transformer protection relay. In this paper, we introduce a number of technical issues, such as a development undertaken in response to the need for an increase in transformer capacity to overcome consequent transmission restrictions, the implementation of a CT saturation countermeasure and the requirement for high-speed operation of the current differential elements. In order to provide solutions to these issues, we have undertaken several developments, which we explain in this paper. Furthermore, with the development of this UHV transformer protection technology, we have been able to complete the commercialization of the transformer protection relay for the 765kV UHV system.

High responsivity and low dark current operation of ultra-small InGaAs MSM photodetector integrated on Si waveguide

We demonstrated a small footprint of 2 × 10 µm2 InGaAs MSM photodetector integrated on Si waveguide with high-efficiency and low dark current property. The detectors have responsivities of 0.94 A/W and the dark current of less than 20 nA, and are capable of 10 Gbps data rate.

Ultralow EMI interconnection module for mobile devices using 3D-flexible hybrid multi-fin optoelectronic FPC

An optoelectronic interconnection module for mobile devices is required to have not only optical interconnection for high-speed and noise-free signal transmission but also many electrical wirings for multiple power supplies and low-speed signal transmission. It leads to great challenges of cost increase, flexibility degradation and electromagnetic noise emission. We propose a novel optoelectronic interconnection module for mobile devices in this paper. A hybrid configuration of an optoelectronic flexible printed circuit (OE-FPC) and an electrical FPC enables to minimize the cost, and a multi-fin structure fabricated by splitting the interconnection area realizes 3D flexibility which is not feasible with a conventional FPC. Magnetic near-field intensities of the optoelectronic interconnection module for mobile devices are shown for the first time. An ultralow-power and ultralow electromagnetic interference (EMI) optical signal transmission performance is demonstrated. It proves that the module developed in this work is highly promising for mobile devices in which signal integrity and EMI are growing into serious problems.