Tunable optical delay with low intensity loss in a cascade structure Er³⁺-doped optical fiber amplifier

In this paper, we propose a new pumping scheme-a dual-frequency laser-pumped cascade structure of Er³⁺-doped optical fiber based on the theory of coherent population oscillation. While realizing slow light transmission, the loss of output signal light power is reduced. Using numerical simulation, we compare the effects of a single fiber without pumping, a 980 nm single pumping single fiber, and a dual-frequency laser-pumped cascade structure of Er³⁺-doped optical fiber on signal light intensity loss coefficient τ and maximum time delay with the increase of input signal light power. The results show that the signal light intensity loss coefficient τ of the three structures decreases gradually with the increase of input signal light power. However, the transmission of lower signal light intensity loss coefficient τ=0.0823 and a larger time delay of 0.15 ms can be obtained under the dual-frequency laser-pumped cascade structure of Er³⁺-doped optical fiber. On the basis of the dual-frequency laser-pumped cascade structure of Er³⁺-doped optical fiber, the signal light intensity loss coefficient τ decreases gradually with the increase of pump ratio M (M=P₁₄₈₀∶P₉₈₀) and the decrease of length ratio N (N=L₂∶L₁; L₁ and L₂ represent the length of the first and second cascaded optical fibers, respectively). Moreover, we compare the effects of ion density of the Er³⁺-doped optical fiber on the time delay of three structures. The dual-frequency laser-pumped cascade structure of Er³⁺-doped optical fiber can provide a larger time delay and smaller signal light intensity loss coefficient τ at low ion density of the Er³⁺-doped optical fiber.