Standard optical coaxial double fiber diameter and refractive index measurement, accuracy, and precision using light scattering at normal incidence.

A plane-polarized laser wave with a wavelength of 441.6 nm illuminates a cladding optical fiber with a diameter of about 18 to 38 mum at normal incidence. A measured angular distribution of the intensity of the scattered wave corresponds well with the differential cross section of a rigorous theoretical calculation of a coaxial double cylinder over a wide range of scattering angle. The diameter and refractive index of the cladding and core of the illuminated part of a fiber have been determined accurately for each uncertainty.