Analysis of the use of saturation tone for spectral gain measurement of erbium-doped fiber optical amplifier

In this thesis, the "saturation tone + small-signal probe" method was experimentally evaluated as a low-cost, fast, and practical alternative for the spectral gain characterization of erbium-doped fiber amplifiers (EDFAs). The study was conducted under 980 nm, 1480 nm, and hybrid pumping (980nm+1480nm) configurations, including forward, backward, and bidirectional schemes. Two input power levels were selected −10 dBm (pre-saturation) and 0 dBm (saturation region) to assess the characterization performance under varying saturation conditions. For each pumping scenario, the obtained gain profiles were compared to reference gain curves measured using a multi-channel CWDM signal. Root Mean Square Error (RMSE) was used to quantify absolute gain differences, while the Pearson correlation coefficient was employed to evaluate shape similarity. Experimental findings showed that, particularly under 0 dBm input power, the saturation effect became prominent, and the gain curves obtained through the proposed method exhibited high agreement with the reference. The lowest RMSE was measured as 0.3397 dB, with the highest Pearson correlation reaching 0.9883. Conversely, under low input power and especially in bidirectional pumping setups, the agreement was limited, with increased RMSE values and observable spectral asymmetries. The results demonstrate that the saturation tone method can generate gain profiles comparable to reference curves under appropriate conditions, revealing its potential as a field-deployable characterization technique without requiring multi-channel test systems. In addition, by analyzing the gain profiles based on their spectral centroid, a quantitative indicator has been identified to support optimum saturation tone selection. This approach aligns with the mathematical modeling objective stated in the thesis and provides a foundation for future development of AI-based predictive systems.