Measurements and calculations of the LP01 intensity ofSM fibers far off the core

Transverse offset measurements with a dynamic range of 10⁶ were performed to determine the autocorrelation of the intensity as a function of the fiber's radial coordinate between 0 and 30 μm. Various matched-cladding, depressed-cladding, and dispersion-flattened single-mode fibers were investigated at wavelengths of 1150, 1300, and 1550 nm. The experimental results are compared to analytical approximations and numerical calculations. Satisfactory agreement for all types of fibers is found if the refractive-index profiles are evaluated carefully and if the wave equation is solved numerically. The results are useful for a realistic estimation of the influence of impurities and imperfections of the substrate tubes used for the plasma chemical vapor deposition (PCVD) process on the attenuation of the fibers