Hydrogen loading and UV-irradiation induced etch rate changes in phosphorus-doped fibers

F D�Rr,G Kulik,S L Semjonov,E M Dianov,R P Salath�,H G Limberger

doi:10.1364/opex.12.005770

Abstract

We show strong changes in chemical etching of phosphorus-doped fiber cores due to hydrogen loading and subsequent UV-irradiation using an atomic force microscope. The etch rate of the fiber core in a low concentration hydrofluoric acid solution (HF) is decreasing after hydrogen loading by as much as 30%. In contrast, UV-irradiation of the hydrogenated fiber increases the core etch rate to values of 27% above the etch rate of the pristine fiber. The UV-induced change in etch rate does not depend on pulse fluence, but only on total dose. We attribute the changes in etch rate to a hydrogen- and radiation-induced modification of color center population.

Highlights

Atomic force microscopy (AFM) of chemically etched fiber end-faces yields topographic information on a nanometer scale due to differential chemical etching of doped and un-doped silica [1,2,3,4]
As the variance in etch rates found within this study is comparable to the variance in molar refractivity reported in [12], the difference in etch rate might be caused by stress or defects introduced into the fiber core during fabrication
Can the increase in etch rate be explained by stress changes? In [4], we reported an increase in etch rate with fiber drawing tension for nitrogen-doped fibers drawn from the same preform

Summary

Introduction

Atomic force microscopy (AFM) of chemically etched fiber end-faces yields topographic information on a nanometer scale due to differential chemical etching of doped and un-doped silica [1,2,3,4]. For germanium-doped fibers it has been shown that the etch profiles can be related to the core-cladding refractive index profile [1,2,3]. Illumination of hydrogen-loaded phosphorusdoped fibers with ArF-laser irradiation at 193 nm results in an increase of the fibers refractive core index [7]. A positive stress change, contributing negatively to the net index change via the photo-elastic effect, has been found for germanium-doped [9] as well as for phosphorus-doped fibers [10]. We present the dependence of etch rate on dopant content for phosphorusdoped fibers as well as changes in etch rate due to hydrogen-loading and subsequent UVirradiation. Our results suggest that the etch rate is predominately governed by the color center population in the fiber core and that changes in etch rate do not necessarily reflect index changes in this fiber

Experiment and results

Findings

Discussion

Conclusion