Secondary Ion Mass Spectrometry Approach for Measuring the Diffusion Range in Optical Fibers with Nanostructured...

A new class of optical fibers with cores composed of various glass nanorods requires a method to determine the internal structure. In particular, the identification of various ion distributions at the fiber cross-section with nanometer accuracy is required. For this purpose, the classical depth profiling mode of the secondary ion mass spectrometry technique is applied. Multiple sampling with various rotation angles allows to retrieve the 1D profile of distribution for particular ions and determine their diffusion ranges. As a proof-of-concept, a nanostructured fiber composed of germanium-doped silica and ytterbium-doped silica rods is measured and the accuracy of the measurement is 3 nm. We show that the average diffusion length of germanium and ytterbium is about 41.5 and 116.6 nm, respectively. It is only 23% and as much as 153% of the initial rod diameter for Ge and Yb ions, respectively. The real diffusion range of particular ions has a significant impact on the refractive and gain media distribution in the fiber and influences the optical properties of the fiber. Therefore, information on diffusion is necessary to design nanostructured optical fibers correctly.