Temperature Dependence of Spectral Properties of Yb-Doped Superfluorescent Fiber Source

Fiber laser has been developed to the point where the average power scaling can reach several kilowatts readily for oscillators and more for amplifiers. In the meanwhile, the thermal effects inside the fiber laser also become prominent. Temperature rise of the fiber core caused by thermal effects has a conspicuous impact on laser performance. In this paper, the spectral properties of superfluorescent fiber sources at low temperature have been studied experimentally and theoretically. We observe a significant flattening of the arc top of the spectra and a broadening to the short-wave direction as the gain fiber temperature decreases from 25 °C to −95 °C. The corresponding 10 dB bandwidth and 20 dB bandwidth increased by 7.216 and 4.004 nm, respectively. The 10 dB center position and the 20 dB center position of the spectrum also move 6.1 nm and 4.2 nm towards short-wave direction, respectively. The absorption and emission cross-sections at different temperatures, calculated based on Lorenz fitting theory, are used to simulate the experimental phenomena, and the results are consistent with the experiment. Additionally, the small signal gain coefficient at low temperature is calculated to help explain the observed phenomena in the experiment.