Abstract

We first investigate the propagation of small signal or pump power in erbium-doped fiber (EDF) with wavelengths corresponding to the absorption bands of EDR It is well known that optical signals suffer high attenuation around 1530 nm, which corresponds to the absorption peak of EDF, such that the signal power decays rapidly and will vanish after propagating through several meters of EDF with erbium concentration around huirdreds of ppm. Yet this is not true for the total power measured by a power meter. Figure 1 shows the total power received by the power meter vs EDF length, which is the simulated result of a -10 dBm input signal at 1532 nm propagating in EDF with 8.9 dB/m at the absorption peak. It is clear that the optical signal power at 1532 nm decays rapidly in EDF; on the other hand, the fluorescence power grows to a level of ~30 dB less than the input signal power, yet it decays slowly at a longer EDF length. Thus the conventional cut-back method cannot apply to EDF loss measurement at longer EDF lengths. This shows that the input power was absorbed by EDF and then converted to fluorescence power spectra at the 1500-nm band due to the phonon interaction of Stark energy levels in EDF at room temperature.¹ Figure 2 shows the optical power measured in forward and backward directions with input power level at -10 dBm and -20 dBm for signal wavelength at 1532 nm and 1550 nm. It can be seen that the forward fluorescence power decays along the EDF while the backward fluorescence power saturates to a level that is almost independent of EDF length.

© 1993 Optical Society of America