Implementation of fluorophoshate laser glass for short length active fiber at 1.5 μm

https://doi.org/10.1016/j.optlastec.2020.106189Get rights and content

Highlights

  • The fluorophosphate laser glass was implemented as short length active glass fiber.

  • The rod-in-tube technique was used for the fabrication of glass fiber.

  • The Tg and refractive index of glasses were optimized to make the glass fiber.

  • The spectroscopic properties of fluorophosphate laser glasses were evaluated.

  • The gain characteristics were demonstrated for fiber amplifier at 1.5 μm.

Abstract

We successfully fabricated a short-length active fiber based on fluorophosphate (FP) laser glass by the rod-in-tube technique and fiber drawing process. The base FP laser glass composition, 20Al(PO3)3-40BaF2-40SrF2 was used for making glass fiber with appropriate core and clad profiles. The physical, thermal, optical, and spectroscopic properties of core and clad materials were optimized in order to implement FP laser glass for active glass fiber fabrication. The difference of refractive index and the glass transition temperature between core and clad glass ingots was obtained to be close to 0.004 and 6 °C, respectively. The spectroscopic properties of FP laser glasses were also derived. The gain and gain coefficient of the indigenously fabricated glass fiber were measured to be 10.29 dB and 0.60 dB/cm at 1550 nm from a 17 cm bare fiber, respectively. The results direct that the short length active fiber based on FP laser glass could be useful for compact all-optical fiber amplifier at 1.5 μm.

Introduction

For the past decades, the optical amplifiers with a high gain coefficient that are based on heavily erbium-doped optical fibers and planar waveguides have attracted great interest. High erbium ion concentration in a guiding core allows the length of the gain medium to be considerably reduced in comparison to the conventional silica fibers. In addition, high output power of the order of several 100 mW can be produced when gain medium is made with high gain coefficients. In this regard, many researchers have carried out researches on the demonstration of short length active fiber [1], [2], [3], [4], [5], [6], [7], [8]. Previous researchers have reported that a high efficient short length active fiber was obtained mainly based on phosphate glass matrix and studied its gain characteristics at around 1.5 μm for-all optical fiber amplifier and laser applications. Unfortunately, the phosphate glasses have high phonon energy that deleterious the performance and lifetime of optical fiber amplifier.

Thus, it is imperative to hunt for a new host matrix that reveals relatively higher emission properties along with firm physical and chemical features. Over the years, the FP glasses have received great attention as stimulated candidates for active device applications as they have favorable properties that include high rare earth (RE) ions solubility, high gain per unit length, low maximum phonon energy, low optical non-linearity and so on [9], [10], [11]. In addition, they possess low glass transition/melting temperatures and viscosity compared to the silica glass. In contrast to the most host matrices that display low RE solubility, the FP glasses allow the manufacturing of short and highly capable fiber amplifiers. The Er3+/Yb3+ co-doped FP glasses have been considered as potential candidates for 1.5 μm near-infrared emission of Er3+ ions because of high energy transfer efficiency (95%) from Yb3+ to Er3+ by means of the large spectral overlap of Yb3+ emission (2F5/2 → 2F7/2) and Er3+ absorption (4I15/2 → 4I11/2). Moreover, Yb3+ ions are used as sensitizers to enhance the pumping efficiency of 980 nm laser diode (LD) emission since Yb3+ exhibits a large absorption cross-section and a broad absorption band between 850 and 1100 nm compared with weak absorption of Er3+ ions [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11].

In this paper, we successfully fabricated a short length active glass fiber and studied its gain characteristics at 1.5 μm for fiber amplifier applications. To fabricate glass fibers, core and cladding materials require optimization of optical and thermal properties. We optimized optical and thermal properties of core and clad materials and found that the properly incorporated cations in the FP glasses and the optimum RE concentrations could offer an optimized combination for the refractive indices and the glass transformation temperature (Tg). The favorable gap of refractive index and Tg was obtained to be close to 0.004 and 6 °C between core and cladding materials. Moreover, spectroscopic properties of FP laser glasses, most importantly, emission cross-section, and lifetime of laser transition (4I13/2 → 4I15/2) were derived.

Section snippets

Experiments and characterization

The regular melt quenching technique was used for the preparation of FP laser glass ingots. The glass compositions of core and clad glass ingots are shown in Table 1. The commercial aluminum metaphosphate and fluorides purchased from Alfa-Aesar, were used as uncooked materials for the synthesis of glasses. Appropriate amounts of chemicals were weighed by microbalance in glove box and pulverized fully using a ball mill (Poong Lim, PL-BM5Ll) for 1 h. Then the even glass composition was cooked in

Viscoelastic properties

It is important to study the viscoelastic properties of glasses for definite applications, especially, glass fiber fabrication process and glass molding process. The viscoelastic response of glasses depends on temperature, frequency, and heating rate [12], [13] and therefore, this study can allow to know the glass transformation, crystallization and melting temperatures. It also allows one to identify the temperature at which a glass must be reheated for specific applications.

Fig. 1 displays

Conclusions

We have successfully implemented a fluorophosphate laser glass for short length active fiber by the rod-in-tube technique and fiber drawing process. The physical, thermal, optical and spectroscopic properties of core and clad materials were evaluated. The most importantly, the difference of refractive index and glass transition temperature between core and clad glass ingots was obtained to be small of the order of 0.004 and 6 °C, respectively. The glass preform was made by the rod-in-tube

Author contributions

FP Laser glass preparation and Analysis, K.L., J.-H.I.; Fiber drawing, D.-B.K., J.-T.A.; FP glass fiber Analysis, Y.C.,Y.-E.I.; Writing - original draft preparation, J.H.C.; Writing - review & editing, K.L., J.H.C. All authors have read and agreed to the published version of the manuscript.

Declaration of Competing Interest

The authors declared that there is no conflict of interest.

Acknowledgment

This work was supported by the Defense Acquisition Programme Administration and the Ministry of Trade, Industry and Energy (Project Number: 14–CM–MP–01), South Korea.

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