High-power Fiber Laser Light-to-optical Conversion Efficiency Improvement Technology Research

Nowadays,the industrialization of the fiber laser is developing rapidly.The fiber laser oscillator has a wide application prospect in industry,military,and many other fields.The enhancement of the Pump Power Conversion Efficiency(PPCE)is of great significance to the fiber lasers.While there are relatively few studies and discussions on this issue.In this paper,the methods to optimize the PPCE of the oscillator are studied from three aspects: the fusing quality of optical fibers,the signal light transmission efficiency of the backward pump signal combiner and the optimization of the resonator parameters.Basing on the mode transmission and the mode energy distribution theory of doublecladding fibers,the model of the power loss caused by fiber splicing in double cladding fewmode fibers is optimized.Aiming at the axial deviation and core diameter mismatch,the experiment of double cladding fiber splicing was carried out.The results show that the optimum model can be used to evaluate the splicing loss of few-mode fibers.Aiming at the problem of low signal light transmission efficiency in backward pumpsignal combiners(PSCs),a model is established to describe the relationship between the core diameter mismatch of signal fiber and power loss caused by splicing in the combiner.By reasonably selecting the parameters of signal fiber in the PSC,the signal light transmission efficiency in backward PSCs is optimized.A backward(6+1)×1 PSC is fabricated and the signal light transmission efficiency is better than 98%.It is used in the reverse pumping structure of MOPA amplifier to achieve 3 kW stable output.According to the rate equations and boundary conditions of the resonator,a simulation model of the influence of pump wavelength,the length of the gain fiber,pump structures and output power on the PPCE of the oscillator is built.By optimizing the parameters above,laser systems were built respectively with the output power of 600 W and 1500 W.The pump power conversion efficiency of the 600 W oscillator is 81.5%.Using a forward-pumping structure with a 976 nm pump source,the oscillator reaches an efficient laser output.The pump power conversion efficiency of 1500 W oscillator is 73%.Through a double-end-pumping structure with a 915 nm pump source,the oscillator achieves a stable output at lower pump power cost.