5-kW-Level Bi-Directional High-Efficiency Pump and Signal Combiner With Negligible Beam Quality Degradation

Abstract

(6+1)×1 pump and signal combiner with high power handing capability, negligible beam quality degradation and bi-directional signal transmission ability has been developed by employing signal-fiber non-taper fabrication approach and in-line active splicing process. The influences of lateral core offset and angular misalignment between the signal input and output fibers in combiner have been studied theoretically, showing that M2 factor rather than signal efficiency is more suitable to be the evaluation criterion. Three splicing methods have been compared experimentally, revealing that the M2-based active splicing is the most effective to preserve beam quality and obtain good efficiency simultaneously. Signal laser transmitted backward through 25-μm fiber core has shown efficiency of 95.5% and M2 factor deterioration no more than 10% at 1 kW of power. Combined pump from laser diodes into 400-μm fiber clad has reached beyond 5 kW of power at efficiency of 98.2%, with the maximum temperature on combiner being 70.5°C, which was tested in the condition without cooling on fiber pigtails and with flat-cleaved fiber termination aggregating thermal load. Both results indicate the effectiveness of the proposed fabrication technique to make bi-directional (6+1)×1 combiner for high power and superior beam quality fiber laser systems.

Keywords

• Bi-directional pump
• fiber combiner
• fiber lasers
• optical fiber devices