Determination of Single-Mode Fiber Refractive Index Profiles by a Propagation Mode Near-Field Scanning Technique

Abstract

The characteristics of an optical fiber, such as spot size, single-mode condition, and dispersion characteristics, are principally determined by its refractive index profile. It is important to establish an efficient and accurate method for measuring the refractive index profile. For a single-mode fiber, however, the measurement of the profile is very difficult because of its small core diameter and low refractive index difference. Several methods were proposed for the measurement of the refractive index profile of single-mode fibers, such as the far-field radiation pattern technique [1],[2], the scattering pattern method [3], the reflection method [4], the focusing method [5], the refracted near-field technique [6], and the interferometric slab method [7].