Design and spectral characteristics of gain-flattened tellurite-based fiber Raman amplifiers

The design and the spectral gain and noise figure (NF) characteristics of tellurite-based fiber Raman amplifiers (FRAs), which are tellurite FRAs (T-FRAs) or hybrid tellurite/silica FRAs (hybrid FRAs), are described. Propagation equations for a multiwavelength (multi-λ)-pumped T-FRA that include the pump interaction terms are presented, with which the gain and NF of the T-FRA can be calculated. Tellurite fiber (TF) length dependences of gain and NF of a T-FRA are clarified experimentally and theoretically. Numerical calculations on the gain and NF spectra of the tellurite-based FRAs show that a T-FRA with a two-stage configuration and a hybrid FRA with a three-stage configuration can provide seamless gain bands with widths of more than 130 nm over the S-, C-, and L-bands. The two-stage T-FRA has a couple of two-λ-pumped T-FRA stages, and a gain equalizer (GEQ) and a dispersion-compensation fiber (DCF) between the T-FRA stages, while the three-stage hybrid FRA has a couple of two-λ-pumped T-FRA stages, and a GEQ and a two-λ-pumped DCF Raman amplifier (DCF-RA) stage between the T-FRA stages. The numerical calculations also show that the two-stage T-FRA and the three-stage hybrid FRA achieve top gains with regard to their flattened gain spectra of 9.7 and 24 dB, and maximum NFs in their gain bands of 11.8 and 8.2 dB, respectively. Measured gain and NF spectra of the tellurite-based FRAs coincide well with the corresponding calculated spectra.