Improvements to the variable aperture method for measuring the mode-field diameter of dispersion-shifted fibers

The variable aperture system for measuring single-mode fiber mode-field diameter is modified to provide accurate measurements of dispersion-shifted fibers. The system´s numerical aperture (NA) is increased by using a spherical mirror and a large aperture wheel with 23 apertures out to 0.556 NA. Petermann´s second mode-field diameter (MFD) definition is calculated with Simpson´s rule numerical integration. The industrialized high-NA variable aperture method in the far field (VAMFF) system is accurate to within 1%, with a measurement standard deviation of less than 0.5%. Flexibility for measuring various fiber designs over a range of wavelengths is also a key feature. It is concluded that the industrialized high-NA VAMFF system is an excellent MFD measurement bench because of its precision, accuracy, and versatility