WDM OPTICAL FILTER AND GLASS SUBSTRATE FOR USE IN THE WDM OPTICAL FILTER

摘要

A glass substrate is for use in a WDM optical filter which has an optic al multilayer coated on the glass substrate and is formed by glass which has a composition related to the optical multilayer so as to assure stable multiplexing/demultiplexing operation in the optical filter. The glass includes SiO2 as a glass network-former and has an average linear thermal expansi on coefficient between 100 x 10 -7/K and 130 x 10 -7/K within a temperature ran ge between -30 .degree.C and +70 .degree.C. The glass may include TiO2, Al2O3, and R20(R: alkali metal element) in addition to SiO2 and may have a hardnes s suitable for the optical multilayer.