Negative-curvature Anti-resonant Fiber Coupling Tolerances

We investigate coupling tolerances of selected designs of negative-curvature anti-resonant fibers (NC-ARFs) with open- and closed-boundary types of structure under linear and angular misalignment of the input near-infrared laser beam. The coupling tolerances of NC-ARFs are compared with those of a commercially available step-index fiber. The expected coupling efficiency for the step-index fiber is calculated using scalar diffraction theory and directly compared with measured profiles. We show that the analyzed NC-ARFs can provide lower sensitivity to input beam misalignment than the step-index fiber, despite having a numerical aperture approximately half of that of the step-index fiber (0.044 compared to 0.07 respectively). In particular, a nodeless design is only half as sensitive to input linear misalignment than the step-index fiber, whilst having an almost identical sensitivity to tilt. A 3.5 μm linear shift and 22 mrad tilt result in 10% decrease in total output power of the beam. The good match between experiment and calculations suggests that the profiles measured for NC-ARFs are correct.