Erbium/thulium doped optical filter for optical fibres or waveguides

摘要

An object of this invention is to provide an optical filter which has higher mass-producibility and economy. This feature can be realized by doping a rare earth element into the region (10) made of a glass material which can transmit light (e.g. optical fiber or waveguide). In a case that Er and Tm are doped as the rare earth element into the region (10), a ratio αEr/αTm between a contribution αEr of Er to attenuation and a contribution αTm of Tm to attenuation is set in a range from about 1 to 1/25 for a 1.5 µm band range, whereby attenuation in this wavelength range is retained above 50 dB/m to realize required cutoff function.