▎ 摘　　要

NOVELTY - The photodetector has a substrate, first, second (241), third (242) and fourth insulating films, and first (237), second, third (261) and fourth (262) high-refractive-index regions. The first to fourth high-refractive-index regions each has a refractive index higher than refractive indices of first and fourth insulating films. The first to fourth high-refractive-index regions and portions sandwiched by high-refractive-index regions constitute an integrated optical waveguide. The first and second electrodes output a current corresponding to light incident on the waveguide. USE - Graphene photodetector. ADVANTAGE - The quantum efficiency can be remarkably improved, since overlap of transverse electric (TE) mode and the portion of the graphene film at which the electric field is high is improved and the current extraction efficiency is also improved. The resistance of megaohm order is inserted in series to the capacitance of the slots, and hence, the leak of the high frequency component of the photocurrent through the parallel capacitors can be suppressed to a negligible level. The carrier transit time can be reduced by reducing the stripe width and the slot width if the process accuracy is high and the displacement is not serious, and the quantum efficiency can be further improved. The optical modulator of a high efficiency, a small size, a high speed and a wide wavelength band can be provided. DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a graphene optical modulator. DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram illustrating a modification of the graphene optical modulator. First high-refractive-index region (237) Second insulating film (241) Third insulating film (242) Third high-refractive-index region (261) Fourth high-refractive-index region (262)