Distance regulation between Tm ions in germanate glass with micro- and macroscopic analysis for efficient S-band fiber amplifiers

In this work, a systematic analytical procedure of Tm-doped germanate glass optimization and corresponding fiber amplifier simulation is established. First, a method for adjusting the Tm-Tm distance in the glass matrix is proposed and validated by molecular dynamics combined with microscopic energy transfer parameters. The results show that the shortest Tm-Tm distance increases from 3.8 Å to 8.5 Å, leading to a weakening of the cross-relaxation (CR) process and an enhancement of the S-band emission of Tm. Secondly, a swarm intelligence algorithm that can derive both the forward and reverse macroscopic CR rates synchronously is established for the first time, to the best of our knowledge. The calculated results show that the forward and reverse macroscopic CR rates are regulated from 0.36(± 0.01) × 10^-22 m³/s and 5.60(± 0.01) × 10^-22 m³/s to 0.30(± 0.01) × 10^-22 m³/s and 7.92(± 0.01) × 10^-22 m³/s, respectively, while the reverse-forward ratio increases from 15.58 ± 0.01 to 26.36 ± 0.01. Finally, the numerical model of the Tm-doped fiber amplifier on the basis of the presented two kinds of germanate glasses is studied. The numerical results indicate that the ASE power in the 1800-nm band can be reduced by enlarging the reverse-forward CR rate ratio, while the S-band amplification effect is improved.