Papers by Author: Tomoyuki Sasaki

Abstract: In this paper, we designed and analyzed an efficient taper structure to couple light into and out of photonic crystal waveguides (PhCWs) fabricated by Si-ion implantation and electron beam lithography. The coupling structure employs the gentle refractive-index distribution produced in the SiO₂ layer by Si-ion implantation. A taper structure is designed for effective coupling of transverse electric (TE) polarized light (λ = 1.55 μm) into a submicron size PhCW consisting of triangular lattice of air holes (lattice constant, a = 0.666 μm, radius of air holes, r = 0.232 μm, waveguide width, W1 ~ 0.7 μm). The influence of the taper length on the transmission characteristics is investigated. Efficiency in excess of 95% is demonstrated using the finite-difference time-domain and beam propagation methods. This is important for their practical applications in photonic integrated circuits.

Abstract: Proton beam writing (PBW) has attracted much attention recently as a next-generation micro-fabrication technology. It is a direct-drawing technique and does not need any masks to transfer micro-patterns to sample surfaces. In addition, the refractive index of a poly (methyl methacrylate) (PMMA) can be increased by proton-beam irradiation. In this study, we fabricated the first 1.5-μm-band single-mode, straight-line waveguides and Y-junction waveguides consisting of PMMA layers using the PBW technique.

Abstract: Light propagation in an optical waveguide fabricated by employing a dye-doped liquid crystal (DDLC) was observed. The propagation of a light signal in the waveguide was varied by irradiation with a control light whose wavelength was in the absorption band of the DDLC. By considering the photothermal effect of the DDLC, which enables the change of the refractive index due to temperature variation based on the absorption of light, we qualitatively explained the observed light propagation and demonstrated manipulation of the propagation.

Abstract: A novel linked thermoelectric system (LTES), fabricated by a simple structural modification of a conventional thermoelectric system (CTES) with the use of conductive metal rods, is characterized experimentally. The LTES generates higher power to the external load in comparison with the CTES, and the power increases with increasing length of the metal rods when the low temperature side of the system is set in the air at room temperature. In addition, measurements of Seebeck voltages of both the systems indicate that the Seebeck coefficient of thermoelectric materials in the LTES is about 1.2 times higher than that in the CTES.