Development of an optical fiber end cap for high-power fiber lasers

In this study, a large-diameter optical fiber end cap was designed and fabricated, which is a critical component of kW-class high-power fiber lasers. To overcome the limitations of conventional electric arc fusion splicing, which restricts the maximum fiber cladding diameter and limits the shape of the end caps to circular geometries, a self-developed CO₂ laser-based fabrication equipment was employed. This highly flexible scheme enabled the successful fusion-splicing of a large-diameter polarization-maintaining fiber (cladding diameter = 400  μm) to a customized 10(W) × 5(D) × 2(H) mm³ silica block. To measure the optical characteristics of the fabricated end cap, it was fused to the output end of a high-power fiber laser. The signal insertion loss of the fabricated end cap was 0.7 %. At an output power of 1.12  kW, the polarization extinction ratio and beam quality were measured as 16.6  dB ± 0.1  dB and 1.13 ± 0.02, respectively, clearly demonstrating the proposed end cap’s structural advantages and suitability for high-power applications.