Reconstruction technology of refractive index and internal stress distribution of multi-core fibers (Invited)

A novel multi-core fiber comprehensive parameter test system based on quantitative phase microscopy method, Brace-Köhler compensator method and machine vision technology was introduced. In order to characterize the test capability of peoposed system, the refractive index distribution and geometric structure of a seven-core fiber from YOFC, and the internal stress distribution of a single-mode fiber from Corning were obtained by this system, respectively. According to the former research, the quantitative phase microscopy method using transverse measurement could avoid the performance  damage  caused  by  truncated  optical fiber efficiently. The improved Brace-Köhler compensatormethod  was  used  to  optimize  the  acquisition  to  get  the optical delay.  Combined  with  the  machine  vision technology,  the  system  realized  multi-modules,  high spatial  resolution,  fast  and  accurate  fiber  parameter measurement. After sample processing, program debugging and optimization, the experiment results show that the accuracy of relative refractive index differencein multicore fiber was about 5×10⁻⁴ magnitude and the internal stress  measurement  resolution  of  single-mode  fiber  wasabout  0.5 MPa.  The  comparison  with  the  technicalindicators of existing optical fiber products proves that the system  has  measurement  accuracy,  and  the  test  results provide  data  support  for  the  application  of  multi-core fibers in multiple fields such as transmission and sensing.