| 摘要 |
PURPOSE:To decrease the fluctuation in radiation angle by a change in wavelength by providing such a means which decrease the equiv. refractive index of a waveguide with a decrease in the wavelength of guided light. CONSTITUTION:This coupler has a clad 3 consisting of material of which the refractive index increases with an increase in the wavelength between the thin film waveguide 2 provided to a substrate 1 and the grating coupler 4. A material which has the refractive index dispersion in dipole absorption near the wavelength lambda to be used, for example, GaAs or the like having exaction absorption is utilized as the material to be used for the layer 3. However a propagating loss alpha increases as well with the absorption center wavelength and, therefore, the wavelength off the central wavelength is required to be used. Since the equiv. refractive index of the thin film waveguide is thereby increased, the fluctuations in both is suppressed. The change in the radiation radiation angle is thus decreased. |
