Determination of metastable state lifetimes of a high-concentration erbium-doped fiber under population inversion conditions at 980 nm pump and 1.5 µm probe wavelengths

We report two-wavelength pump-probe measurements of the metastable state lifetime in a high-concentration erbium-doped fiber (EDF). The lifetimes under population inversion conditions are measured using a 980 nm pump laser and a 1.5 µm probe laser. The lifetime variation from the lifetime under low excitation conditions to that of a highly inverted population are calculated using a model derived from the rate equations. To confirm the validity of our method, we compare the results obtained with those for temporally resolved spontaneous emissions in the perpendicular direction and those measured using a 1.5 µm single-wavelength pump–probe technique in our previous work.