Multi-layer film filter-use substrate glass and multi-layer film filter

摘要

A substrate glass for a multilayer filter is 150 nm or less in flatness within a circle of diameter 50 mm and has a thermal expansion coefficient of 90 to 130x10<-7>/° C. at temperatures of -30 to 70 ° C. The substrate glass 150 nm or less in flatness within a circle of diameter 50 mm provides less variations in thickness of film layers. When a plurality of multilayer filters are fabricated from a single sheet of the substrate glass, variations in center wavelength fall within the range of ±100 pm among the multilayer filters, thereby providing improved production yields for the multilayer filters.