Fiber lasers have a broad application prospect in various fields for their excellent pump power conversion efficiency and beam quality, as well as the compact structure and simple thermal management. Recently, commercial fiber laser systems have emitted an output of tens of kilowatts through a master oscillator power amplifier (MOPA) structure^[1]. In order to achieve a higher output power, the pump combiner (PC) and pump-signal combiner (PSC) are widely used, the requirements for their signal light transmission efficiency and stability are also increasing^[2-4]. According to their structure and function, the combiners can be divided into N×1 PCs and (N+1)×1 PSCs. The former can couple multi-channel pump light into a signal fiber, mostly used in the forward-pumping structure of fiber oscillator, while the latter can couple signal light together with the multi-channel pump light into the signal fiber, to realize the signal light transmission and pump power injection of oscillator reverse-pumping structure and MOPA amplifier.