Fabrication and Characterization of Er/Yb Co-Doped Fluorophosphosilicate Glass Core Optical Fibers

Denis S. Lipatov,Mikhail E. Likhachev,Maxim M. Khudyakov,Andrey A. Umnikov,Alexey N. Abramov,Alexey N. Guryanov,Oleg G. Morozov,Alexey S. Lobanov

doi:10.3390/fib9030015

Abstract

The technical process of the synthesis of a fluorophosphosilicate (FPS) glass core was thoroughly investigated for the first time utilizing a modified chemical vapor deposition (MCVD) all-gas-phase fabrication method. It was discovered that the limiting doping level of the silica glass simultaneously co-doped with phosphorus (P) and fluorine (F) was found to be confined by the formation of POF3 gas. The dopants content was achieved as high as 4.7 at% of P and 1.1 at% of F in a glass core, respectively. A developed “in-house” manufacturing method makes it possible to fabricate a large mode area (LMA) purely single-mode Er–Yb co-doped optical fibers with a core diameter of 20 μm and with a lasing efficiency comparable to commercially available LMA Er–Yb optical fibers.

Highlights

IntroductionThe emission wavelength range in the vicinity of 1.5 μm is “eye-safe” (as compared to the 1 μm spectral range of Yb-doped fiber lasers), which overlaps with the maximum optical transparency of silica glass and is widely used in various practical applications, i.e., related to signal propagation in the atmosphere, such as LIDAR (light detection and ranging)
The emission wavelength range in the vicinity of 1.5 μm is “eye-safe”, which overlaps with the maximum optical transparency of silica glass and is widely used in various practical applications, i.e., related to signal propagation in the atmosphere, such as LIDAR
The maximum efficiency of the energy transfer of excitation (ETE) from Yb3+ to Er3+ ions is observed in the phosphosilicate glass matrix, due to the rapid relaxation of Er3+ ions from the level to which the energy is transferred from Yb3+ ions and reverse energy transmission is almost excluded

Summary

Introduction

The emission wavelength range in the vicinity of 1.5 μm is “eye-safe” (as compared to the 1 μm spectral range of Yb-doped fiber lasers), which overlaps with the maximum optical transparency of silica glass and is widely used in various practical applications, i.e., related to signal propagation in the atmosphere, such as LIDAR (light detection and ranging). The most common sources of laser radiation at a wavelength of 1.5 μm are typically silica fiber lasers and amplifiers based on double-clad optical fibers of an Er2 O3 –. Yb2 O3 –P2 O5 –SiO2 glass core composition In this particular fiber design, Yb3+ ions are capable of efficiently absorbing the pump power (915/980 nm) from the first reflective cladding and transfer energy to Er3+ ions. The sufficiently high refractive index of this glass (numerical aperture (NA)~0.2) imposes a reduction in the core diameter in a single-mode fiber (4–7 μm) and an increase in the active fiber length (5–20 m) for maintaining efficient pump absorption. The threshold of nonlinear effects is dramatically reduced, which limits the output power of lasers to ~100 W [2], and eventually Er–Yb-co-doped fibers are not used for designing pulsed laser sources

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Discussion

Conclusion