Method for measuring the resonant absorption coefficient of rare-earth-doped optical fibers

A nondestructive method for measuring the resonant absorption coefficient of rare-earth-doped optical fibers is introduced. It can be applied to a broad range of fiber designs and host materials. The method compares the side-collected spontaneous emission at two arbitrary locations along the fiber as a function of the pump wavelength to extract the absorption coefficient. It provides an attractive and accurate alternative to other available techniques. In particular, the proposed method is superior to the cutback method, which destroys the sample and is prone to inaccuracies due to the cladding mode contamination. Moreover, because it does not involve any mechanical movement, it can be used for fragile optical fibers.