Improvement of beam quality in the far-field of annular core optical fibers by realizing single-mode operation

We have improved the beam quality by realizing single-mode operation in the annular core optical fibers (ACF), and discuss the relations between single-mode and its design parameters. Moreover the effect of the thickness of the guiding section on the energy distribution in the far-field is analyzed. With proper parameters design, more than 99% of the annular light emitted from ACF could be centralized at a bright spot in the far-field. These results may provide a theoretical guidance for the design and application of ACF.