PURPOSE: To enhance the stability of an optical waveguide path by interposing a buffer layer having a gradually changing expansion coefficient between a glass layer and a substrate for the path to reduce the strain.
CONSTITUTION: On substrate 1 B2O3-SiO2 glass layer 2 is formed while gradually increasing the B2O3 content 0W10% in the through thickness direction, and lower clad layer 3 contg. 10% B2O3 is formed. Core layer 4 contg. 10% GeO2 and upper clad layer 5 contg. 10% B2O3 are then formed in order. In this structure an optical waveguide path section is composed of layers 3, 4, 5, and layer 2 changing the expansion coefficient is interposed between substrate 1 and optical wabeguide path sections 3, 4, 5. Thus, the strain is reduce considerably to prevent the breakdown of the optical waveguide path.
MORI HIDEFUMI
SHIMIZU NOBUO
MURAKAMI TAIJI
