Metastable-state lifetime of erbium ions measured in the fiber propagation direction: Expansion of measurable fiber length

We report the measurement of the metastable-state lifetime of erbium ions doped in a fiber. We apply the pump–probe technique with a wavelength-tunable laser array. This technique allows us to measure the lifetime through delayed absorption in the fiber propagation directions. By tuning the wavelength of the pump–probe pulse pairs to a low absorption wavelength, the lifetime of the metastable state is successfully measured in a 5-m-long fiber. The lifetime is determined to be 10.0 ms, which agrees well with previously reported values.