Highly doped multicomponent phosphate glass fibers for compact pulsed optical amplifiers

In recent years, there has been a growing interest towards compact high peak-power pulsed laser sources for applications such as LIDAR, range findings, remote sensing, communications and material processing. A common laser architecture used to realize these sources is the Master Oscillator Power Amplifier (MOPA), in which a master oscillator produces a highly coherent beam and a fiber amplifier boosts the output power, while preserving its main spectral properties. Phosphate glasses are recognized to be an ideal host material for engineering the amplification stage of a pulsed MOPA since they enable extremely high doping levels of rare-earth ions to be incorporated in the glass matrix without clustering, thus allowing the fabrication of compact active devices with high gain per unit length. With the aim of realizing compact optical fiber amplifiers operating at 1 and 1.5 µm, a series of highly Yb3+- and Yb3+/Er3+-doped custom phosphate glass compositions were designed and fabricated to be used as active materials for the core of the amplifiers. Suitable cladding glass compositions were explored and final core/cladding glass pairs were selected to realize single-mode and multi-mode optical fibers. Core and cladding glasses were synthesized by melt-quenching technique. The core glass was then cast into a cylindrical mold to form a rod, while the cladding glass was shaped into a tube by rotational casting method or extrusion technique. The latter has been extensively employed for the manufacturing of tellurite and germanate glass preforms, but only recently the first example of active phosphate fiber preform fabricated by this method has been reported by our research team. Phosphate fibers were then manufactured by preform drawing, with the preform being obtained by the rod-in-tube technique. Preliminary results of pulsed optical amplification at 1 and 1.5 µm are presented for a single-stage MOPA.