Optical filter doped with rare earth elements and used with optical fibers

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 doped a rare earth element into the region made of a glass material which can transmit light. In a case that Er and Tm are doped as the rare earth element into the region, a ratio alpha Er/ alpha Tm between a contribution alpha Er of Er to attenuation and a contribution alpha Tm of Tm to attenuation is set in a range from about 1 to 1/25 for a 1.5 mu m band range, whereby attenuation in this wavelength range is retained above 50 dB/m to realize required cutoff function.