Fabrication of Waveguide Core by Dispersal of Compound with Higher Refractive Index by Vacuum Process

Abstract

The “vapor transportation method,” a process for doping dye into polymers, enables us to prepare a favorable doped layer in a polymer. The doped layer had both a uniform dye concentration and a smooth surface. As a further development, we expanded the present method for use in the preparation of an optical waveguide. For the preparation of the waveguide, a low-molecular-weight compound (phenyl benzoate, PB) with a high refractive index was dispersed in a matrix polymer [poly(methyl methacrylate), PMMA] through a mask. After dispersion, the mask was removed, and another PMMA plate was placed on the doped plate using a vacuum thermal press. The double-layered structure of the doped and nondoped regions was clear in the cross section. The two regions described were transparent. A beam incident onto the edge of the doped region of the prepared sample emerged from the other edge, indicating that the doped regions acted as a core. The core radius (depth of the doped region) increased with treatment time and treatment temperature. Furthermore, the refractive index of the core was controlled by the treatment temperature. The fabricated waveguide showed a propagation loss of 0.47 dB/cm at 650 nm.