Amplification of single-frequency signals in bismuth-doped optical fibers with single-mode and multimode pumping

The possibility of amplifying a single-frequency signal at a wavelength of 1367 nm in bismuth-doped optical fibers with single-mode (laser using the nonlinear optical effect of stimulated Raman scattering, Raman laser) and multi-mode (laser diodes) pumping has been investigated. The use of a Raman fiber laser with a radiation wavelength of 1205 nm and a power of ∼2 W, and bidirectional pumping injected into the core of a single-mode bismuth-doped optical fiber increased the signal power from 11 to 342 mW (gain of ∼15 dB). An output signal power of 155 mW (gain of ∼11.5 dB) was achieved using multimode laser diodes with a wavelength of 793 nm injected into the cladding of an active single-mode optical fiber. In both cases, the spectrum of the single-frequency signal was not distorted after amplification when measured using a spectrum analyzer with a hardware function of 20 pm, while the relative intensity noise (RIN) of the amplifiers did not exceed –140 dB/Hz.