Non-destructive characterization of rare-earth-doped optical fiber preforms

We present a non-destructive optical technique for rare-earth-doped optical fiber preform inspection, which combines luminescence spectroscopy measurements, analyzed through an optical tomography technique, and ray-deflection measurements for calculating the refractive-index profile (RIP) of the sample. We demonstrate the technique on an optical fiber preform sample with a Yb³⁺-doped aluminosilicate core. The spatial distribution of the photoluminescence signals originating from Yb³⁺-single ions and from Yb³⁺-Yb³⁺ cluster sites were obtained inside the core. By modifying the characterization system, we were able to concurrently evaluate the RIP of the core and, thus, establish with good accuracy the dopant distribution within the core region. This technique will be useful for quality evaluation and optimization of optical fiber preforms.