Design of 1018nm Fiber Laser

Design of 1018nm Fiber Laser
The 1018nm fiber laser is commonly used as the pump source for cascaded high-power ytterbium doped fiber laser. In the direct pumping scheme, a 976nm semiconductor laser is generally used as the pump source. To achieve higher power ytterbium doped fiber lasers, increasing the power of the pump light source is an important means. However, the 1018nm fiber laser is limited by the amplified spontaneous emission effect, and the output power has been difficult to significantly increase. Researchers have achieved a 2kw level 1018nm fiber laser by optimizing parameter design.
1.Theoretical Analysis and Design
The schematic diagram of the experimental optical path is shown below. The pump source uses a 976nm wavelength locked semiconductor laser WS-LD. Each WS-LD can provide approximately 250W of pump power, which is coupled into a ytterbium doped fiber resonator through a combiner. The entire system adopts a bidirectional cascade pumping scheme. Through theoretical calculations and simulations, the relevant parameters of ytterbium doped fiber (YDF) and fiber Bragg grating (FBG) were analyzed in depth, and the variation laws of output characteristics such as laser output power, optical to optical conversion efficiency, and ASE suppression ratio (SAR) were obtained, and the optimal parameter values were determined.

Firstly, the relationship between laser output characteristics and ytterbium doped fiber length, pump light absorption coefficient, and related numerical values are calculated; Secondly, the relationship between laser output characteristics and ytterbium doped fiber length, output coupling grating OC-FBG reflectivity, and the calculation of relevant values; Finally, the relationship between fiber winding diameter, conversion efficiency, and output optical field distribution is discussed, and relevant numerical values are calculated.
2.Result
The final plan selected YDF of 2.6m and grating reflectivity of 99.5% and 20%, respectively. The fiber winding diameter is 8cm. The forward and backward pump powers are 1500W and 1040W, respectively, with an output power of 1940W and a light to light conversion efficiency of 76.38%. At the same time, researchers also discovered the instability effect of TMI mode in practical experiments, and increased the threshold of TMI by reducing the winding diameter to suppress the TMI effect.