| 摘要 |
PURPOSE:To reduce the transmission loss in each waveguide passage by forming preset first and second waveguide passages in a crossing and passing manner on a waveguide film which is formed on a substrate. CONSTITUTION:A waveguide film 12 of a refractive index of n2, through which waveguide lights 22a and 22b of wavelength lambda is to pass, is formed on a substrate with a cut-off film thickness for that wavelength lambda. The film 12 is heated with a laser beam, and a pair of parallel preset portions 21a to 21d having a refractive index of (n2-DELTAn), which are arranged at a preset spacing, thereby to form such first and second waveguide passages 23a and 23b as cross and pass through each other. If the portion 21d of the crossing portion 7 is taken into consideration, the transmission loss for the light 22a is expressed by Fresnel reflrection with the use of a formula, because the incidence angle of the light 22a is substantially at a right angle with respect to the portion 21d, so that the value can be such a negligible level as is lower than 10<->4. As a result, the loss in the portion 21c for the light 22a and the losses of the portions 21a and 21b for the light 22b are similar so that no substantial loss takes place. |
