Profilometry of an optical microfiber based on modal evolution.

The waist diameter of a tapered optical fiber (TOF) has been determined using the modal evolution during the tapering process of a single-mode optical fiber (SMF28) through the short-time Fourier transform (STFT) analysis. The STFT was utilized to calculate the cutoff moment of the different modes. By the knowledge of the cutoff diameter, the final diameter of the waist with accuracy better than 5 nm was measured. The TOF shape depends on the flame parameters, the material properties, and the stretching conditions. By calculating the TOF deformation rate of the TOF, the diameter of TOFs near the waist has been measured with an accuracy of 6.1%; moreover, the TOFs were fabricated with a non-uniform flame.