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In this paper, highly (up to 5.25 mol% Er 2 O 3) Er-doped phosphate bulk glasses were synthesized by conventional melt-quenching method and their physical, thermal and spectroscopic properties are reported. The influence of Er 3+ doping concentration on emission spectra and lifetimes was investigated in order to study the concentration quenching effect on luminescence performance and therefore to evaluate the most suitable rare earth content for developing compact fiber fibre laser and optical amplifier operating at 1.5 µm. A radiative lifetime and a quenching concentration equal to τ 0 = 7.05 ms and N 0 = 9.92 × 10 20 ions/cm 3 were respectively calculated by fitting the fluorescence lifetime experimental data with Auzel's limited diffusion model.

Optical fibers have recently attracted a noticeable interest for biomedical applications because they provide a minimally invasive method for in vivo sensing, imaging techniques, deep‐tissue photodynamic therapy or optogenetics. The silica optical fibers are the most commonly used because they offer excellent optical properties, and they are readily available at a reasonable price. The fused silica is a biocompatible material, but it is not bioresorbable so it does not decompose in the body and the fibers must be ex‐planted after in vivo use and their fragments can present a considerable risk to the patient when the fiber breaks. In contrast, optical fibers made of phosphate glasses can bring many benefits because such glasses exhibit good transparency in ultraviolet‐visible and near‐infrared regions, and their solubility in water can be tailored by changing the chemical composition. The bioresorbability and toxicity of phosphate glass–based optical fibers were tested in vivo on male laboratory rats for the first time. The fiber was spliced together with a standard graded‐index multi‐mode fiber pigtail and an optical probe for in vitro pH measurement was prepared by the immobilization of a fluorescent dye on the fiber tip by a sol‐gel method to demonstrate applicability and compatibility of the fiber with common fiber optics.

Abstract:In recent years, the exploitation of compact laser sources and amplifiers in fiber form has found extensive applications in industrial and scientific fields. The fiber format offers compactness, high beam quality through single-mode regime and excellent heat dissipation, thus leading to high laser reliability and long-term stability. The realization of devices based on this technology requires an active medium with high optical gain over a short length to increase efficiency while mitigating nonlinear optical effects. Multicomponent phosphate glasses meet these requirements thanks to the high solubility of rare-earth ions in their glass matrix, alongside with high emission cross-sections, chemical stability and high optical damage threshold. In this paper, we review recent advances in the field thanks to the combination of highly-doped phosphate glasses and innovative fiber drawing techniques. We also present the main performance achievements and outlook both in continuous wave (CW) and pulsed mode regimes.Keywords: fiber laser and amplifier; phosphate fiber; all-fiber master oscillator power amplifier (MOPA); rare-earth-doped fiber