High-power fiber lasers have been widely used in industrial processing, automobile manufacturing, national defense, scientific research, and other fields. It has been ten years since IPG Photonics demonstrated the fiber laser output of 20 kW in 2013, which is an important milestone. However, it has also marked a dark cloud in the field of high-power fiber lasers. Although fiber laser is still in full swing, it was not until 2021 that very individual units tied the record, let alone made breakthroughs. The higher output power of the laser indicates more waste heat produced in the laser, which brings thorny transverse mode instability (TMI) and many nonlinear effects such as stimulated Raman scattering (SRS), Brillouin scattering. This is a strong negative feedback mechanism, which means that it will be harder to improve the output power. Under the current limited conditions, high stability fiber laser has gradually become a demand, and researchers have gradually carried out in-depth research on the influence of temperature on fiber lasers.

First, the research and results of the influence of temperature on optical fiber devices are discussed. The influence of temperature on LD is clear and direct, including the change of power and the drift of central wavelength. Optical fiber is different. The influence of small structural changes of optical fiber on devices such as gratings and combiners is difficult to be determined qualitatively. The physical parameters of optical fiber, such as thermal expansion coefficient, thermal diffusion coefficient, thermal conductivity, critical absorption, and emission cross sections, are difficult to be measured accurately. The experimental results of the central wavelength of laser diodes, the reflectivity of fiber grating, and the absorption and emission cross section of gain fiber with temperature are displayed, which is very helpful to simulate the behavior of laser at different temperatures.

Second, the research on the output efficiency of fiber lasers in a wide temperature range in China and abroad is reviewed. Among them, more studies focus on the temperature range higher than normal temperature. Under this condition, the efficiency of fiber lasers with longer wavelengths can be improved. On the contrary, some studies are based on cryogenic media such as liquid nitrogen to cool gain fibers, which often contribute to shorter-wavelength lasers. These studies are generally at a low level of output power, basically less than the order of 100 W, and the main body of temperature control is ytterbium-doped fiber (YDF).

Third, the experimental study on the effect of temperature on TMI and SRS of fiber laser is illustrated. As for TMI, the increase in the TMI threshold can be observed by fully strengthening YDF refrigeration. However, in some experimental studies, when the change in YDF cooling is not obvious, it is difficult to find the change in the TMI threshold. The influence of temperature on TMI is affected by laser structure, gain fiber type, fiber bending state, cooling condition, etc. The mechanism of the effect of operating temperature on the TMI threshold of fiber laser needs to be further studied. As for SRS, two experimental studies have demonstrated that lowering the temperature of YDF can inhibit SRS. At present, the preliminary analysis claims that the decrease in the working temperature of the optical fiber suppresses the spontaneous Raman noise and increases the stimulated Raman scattering threshold.

Forth, the research results of fiber lasers with high power and wide temperature operation in our research group are introduced. Due to the lack of research on the low temperature at present, our research group has carried out research on fiber laser which is at a wide temperature lower than room temperature based on the high-power fiber laser above kw level. In 2020, our research group demonstrated a fiber laser oscillator of 2 kW, which can maintain stable output in the temperature range of -10-20 ℃, and the power fluctuation is less than 7%. In 2021, our research group realized a kilowatt optical fiber oscillator with output power fluctuation of less than 7% in the range of -30-20 ℃.

The characteristics of compact structure, small size, light weight, and flexible operation contribute to the high ease of use of fiber lasers. Due to the stagnation of the maximum output power, the development of a wider temperature range and more stable output power will become one of the development trends of optical fiber laser technology in the coming period. Further expansion of the power and operating temperature range also requires in-depth study of the working mechanism of fiber lasers and the temperature characteristics of fiber devices. The development trend of wide-temperature operating fiber laser is prospected, and the research results provide a reference for the development of high-power wide-temperature operation fiber laser.