Pump excited-state absorption in erbium-doped fibers.
Ground-state and excited-state absorption spectra covering the wavelength range of 450-1050 nm are presented for erbium-doped silica fibers with four different core codopants: GeO(2), GeO(2)/B(2)O(3), GeO(2) /P(2)O(5), and Al(2)O(3). It is shown that the host glass influences the excited-state absorption spectra and that P(2)O(5)- or A1(2)O(3)-codoped fibers are the preferred choice for 514.5-, 655-, or 807-nm pump wavelengths owing to reduced pump excited-state absorption. However, excited-state absorption is still significant at the 807-nm wavelength. Pump wavelengths of 524, 532, and 980 nm appear ideal because of the strong ground-state absorption and lack of excited-state absorption.
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