Low noise laser sources with narrow linewidth and low intensity noise are key tools in a broad range of applications such as optical sense, microwave photonics, coherent optical communications and so on. The report gives an introduction about our research progress of the narrow-linewidth single frequency DFB fiber lasers. An internally developed DFB fiber laser is developed. The noise characteristic of laser output is studied in detail. The frequency noise in low Fourier frequency is reduced via using the low noise pump and intracavity optical negative feedback. Furthermore, an injecting lock scheme is used to reduce the intensity noise. A fiber laser output with low frequency noise and low intensity noise has been demonstrated.
A compact short-cavity fiber laser configured with
Er<sup>3+</sup>/Yb<sup>3+</sup> highly co-doped phosphate glass fiber which has linear
polarization and single frequency output is fabricated experimentally. The threshold power of the laser is about 30mW,
and larger than 100mW output power is achieved with slope efficiency of 20% at 1549nm. At the meantime, sine
modulation, positive pulse and chaos state in the output power at different experimental condition are observed. And a
new theoretical model is proposed to describe the mechanism of the observed intensity instability behavior in the fiber
laser and the numerical results proved its feasibility. It is confirmed that the self-pulsing behavior is mainly caused by
different small external feedback. So there is an efficient way to overcome self-pulsing behavior in the compact single
polarized fiber laser by minimizing the external feedback.