Submount with filter layers for mounting a bottom-incidence type photodiode

摘要

A submount including a transparent substrate and at least one wavelength selective absorption layer being piled upon the substrate and having a band gap wavelength lambdg1 which is shorter than the necessary light wavelength lambd2 but longer than the unnecessary light wavelength lambd1. The submount is inserted between a case (package, metallized pattern) and a bottom incidence PD for insulating the PD from the case and for admitting only the necessary light.