Instrumentation for Simultaneous Non-Destructive Profiling of Refractive Index and Rare-Earth-Ion Distributions in Optical Fiber Preforms

Marilena Vivona,Michalis Zervas

doi:10.3390/instruments2040023

Abstract

We present a non-destructive technique for a combined evaluation of refractive index and active-dopant distribution in the same position along a rare-earth-doped optical fiber preform. The method relies on luminescence measurements, analyzed through an optical tomography technique, to define the active dopant distribution and ray-deflection measurements to calculate the refractive index profile. The concurrent evaluation of both the preform refractive index and the active dopant profiles allows for an accurate establishment of the dopant distribution within the optical core region. This combined information is important for the optimization and development of a range of advanced fibers, used, for example, in a high-power fiber lasers and modern spatial-division-multiplexing optical communication systems. In addition, the non-destructive nature allows the technique to be used to identify the most appropriate preform segment, thus increasing fiber yield and reducing development cycles. We demonstrate the technique on an Yb3+-doped aluminosilicate fiber preform and compare it with independent refractive index and active-dopant measurements. This technique will be useful for quality evaluation and optimization of optical fiber preforms and lends itself to advanced instrumentation.

Highlights

Fiber lasers and amplifiers have reached out and truly transformed a number of diverse engineering sectors, such as industrial material processing, civil applications, environmental monitoring, and even devices suitable for space missions
To demonstrate the new technique, we used an optical fiber preform manufactured by a modified chemical vapor deposition (MCVD) process with an optical core made of aluminosilicate glass and doped with Yb3+ by the solution doping technique with a nominal Yb3+ concentration in the low
The characterization was performed in the same section of the optical preform, without moving any part of the experimental set-up, except a small translation of the CCD camera in order to adjust the chromatic dependence of the lens focal length

Summary

Introduction

Fiber lasers and amplifiers have reached out and truly transformed a number of diverse engineering sectors, such as industrial material processing (e.g., micromachining, welding, engraving, and cutting [1]), civil applications (e.g., telecommunications, medical imaging, and surgery [2]), environmental monitoring (e.g., temperature detection and radiation dosimetry [3,4]), and even devices suitable for space missions (e.g., gyroscopes and amplifiers [5,6]). In order to further enhance the performance of RE-doped fiber-based devices, a number of features, such as advanced pumping schemes and fiber designs with improved optical properties, should be developed. Improvement of the RE-doped fibers and fiber production scaling up are closely linked to the optimization of the manufacturing of the preforms from which the optical fibers are drawn. This is relevant in the case of the conventional and widely used active fiber fabrication method, based on the modified-chemical vapor deposition (MCVD) combined with an RE-doping solution [8,9]. The applicability and efficiency of this method can be potentially

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