The impact of fiber fusion splicing on the focal ratio degradation and transmission of LAMOST fiber system

Abstract

We report results of the impact of fiber fusion splicing on Focal Ratio Degradation (FRD) and transmission loss of Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) fiber system. We test at f/5 input f-ratio conditions, the influence of fiber fusion splicing on FRD and transmission respectively in the laboratory. A precision test system was designed to reduce the system error and human error. The measurement accuracy of the system reaches micron scale. The fiber end surface was prepared by large core fiber cutter, grinder and fusion splicing workstation. The fiber surface roughness is less than 1 micron and the surface angle is less than 0.5°. By optimize the cutting and polish process, adjusted the fusion parameters, a satisfactory results of optical fiber fusion obtained in the laboratory. The maximum transmission increase caused by the fiber fusion is less than 3%, average value is about 1%; while the maximum FRD increase is about 0.12°. We repaired 14 damaged optical fibers of LAMOST fiber system by use fiber fusion method, and the average peak light intensity of the repaired fiber reaches more than 90% of the peak light intensity of the normal use fiber in action. Our results indicate that fiber fusion technology can be adopted for repair failure optical fiber, replace the fiber clips and astronomical instrument construction.