The optimization of incoherent fiber laser beam combination

Abstract

With the continuous increase of output power of double cladding fiber lasers, the researches of the techniques of fiber laser beam combination have become a new focus. With the inherent characters of small volume, light weight, good beam quality and system stability. Once the high power output laser was achieved, there would be broad applications in industry, scientific researches and military field. Incoherent beam combination is much easier to be realized compared with coherent beam combination, and with better system stability, thus it became an promising technique to achieve small volume and high power laser source. In an incoherent fiber laser beam combination system, the transform lens and diffractive grating play an important role in determining the coupling efficiency. Through theoretic analysis and numerical simulations, it has been proved that the optimum focal length of transform lens should be around 20cm in order to ensure a high system coupling efficiency under some selected simulation parameters. Also the lower frequency of diffractive grating is preferred, and a contradiction is present that is the higher frequency of diffractive grating is favorable in the consideration of maximum fiber array width, thus a moderate value was chosen as 200mm-1 with comprehensive consideration. The lower grating thickness is helpful in improving the diffractive efficiency, while it faced the problem of heat resistance and manufacturing difficulty, therefore the grating thickness between 2mm and 4mm is preferred. Under such optimized parameters, the coupling efficiency would be 70% or even higher with small deviation angle and wavelength. An example of effective jamming distance of combined fiber laser to visible light silicon CCD has been given, whose results had proved the application foreground of combined fiber laser.