Yoshihiro Sekimoto

Fabrication Method of Double-Microlens Array Using Self-Alignment Technology

A fabrication method for double-microlens arrays with self-alignment technology (SAT) is proposed. To satisfy the tolerance of the alignment of a two-layer-lens array, we developed a new fabrication method without an alignment process. Using SAT, we achieved a brightness increase of 30% compared with the conventional single-layer microlens array.

Water Purification Using the Adsorption Characteristics of Microbubbles

Recently, technology using microbubbles has been studied for water purification. However, the mechanism and physical parameters of the purification process have not yet been sufficiently clarified. The purpose of this study is to clarify the physical parameters of microbubbles that influence water purification. Firstly, we measured and analyzed the purifying performance using various millimeter-sized bubbles, and we obtained the equilibrium constant of the pollutant adsorbed on the bubble surface from the experimental results. Secondly, we experimented with purifying the polluted water using microbubbles and clarified that the purification performance of microbubbles agreed with that theoretically expected using the equilibrium constant obtained in the preparatory experiment. We assume that an important parameter affecting adsorption on the surface of microbubbles is the equilibrium constant in the chemical potential. Because the equilibrium constant is derived from the surface chemical potential, it is equal to the bulk chemical potential of the liquid. In the microbubbles diameter (70 µm) range in this study, we have found that the most significant factor determining the adsorption is the surface area. The surface tension of microbubbles is not significant factor.

Micromachined Silicon Submount for Optical Communication Devices

In this paper, we report the development of a new surface mount structure for optical communication devices using micro-electro-mechanical system (MEMS) technologies. We have designed and fabricated a silicon submount by wet anisotropic micromachining techniques. We have surveyed the main design parameters of this submount as an example against optical and thermal effects by computer simulations and experiments. We have mounted a light-emitting diode (LED) for plastic optical fiber (POF)-based optical communication systems on the silicon submount and evaluated the optical and thermal properties of this submount, indicating that the radiation half width at full maximum (HWFM) angle of the LED decreased from 60 to 40°. Additionally, we have observed a 60% reduction in the thermal resistance of the LED while keeping its thermal reliability.

Mini Disc Optical Pickup Integrated with a Birefringence Wedge and a Holographic Optical Element

Using a compound prism with a holographic optical element and a birefringence wedge, we have developed a twin-spot method pickup for a Mini Disc player. Since tolerance sharing is optimized by ray trace simulation, servo signal offsets caused by assembly error and fabrication error are compensated simply by positioning and rotating the compound prism in a plane; however, all servo and magneto-optical (MO) signals are detected by a photodiode. Although two half-wave plates are placed in the diverging light beam, it is theoretically and experimentally revealed that they hardly deteriorate the MO signals. The jitter value of the MO signal reproduced by this pickup reached 19 ns.