Novel Technique for Measuring the Index Profile of Optical Fibers

Abstract

A novel technique for measuring the refractive index profile of optical fibers is demonstrated, which offers substantial advantages over alternative methods. The method consists of illuminating a small area of the fiber core and measuring the total transmitted power. The transmission of leaky modes is accounted for in the manner reported previously by other authors. The index profiles of germanium-doped fibers obtained by this technique are compared to interferometric measurements. The resolution is shown to be limited by wave optics effects to about λ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</inf> (4n√2Δ) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> , where Δ ≡ Δn/n. The distortion of the index profile as the wavelength varies and wave-optics effects are investigated.