Nd 3+ -doped fluoroaluminate glasses for a 1.3 μm amplifier

A ${\mathrm{Nd}}^{\mathrm{3+}}$ -doped 1.3 μm fiber amplifier has the potential to be an efficient, high-gain device. A major problem to overcome is the long wavelength of the gain spectrum. In the majority of ${\mathrm{Nd}}^{\mathrm{3+}}$ -doped glasses the gain is shifted out of the second telecom window as a result of long-wavelength emission and signal excited-state absorption (ESA). In this article we present new fluoroaluminate glasses developed as hosts for the 1.3 μm ${\mathrm{Nd}}^{\mathrm{3+}}$ -doped fiber amplifier. ${\mathrm{Nd}}^{\mathrm{3+}}$ emission peaks below 1320 nm were demonstrated in bulk glasses. Gain in the 1310–1320 nm region was measured in unclad fibers, with evidence of significantly reduced ESA. Another serious problem in amplifier design lies in overcoming the competing amplified spontaneous emission (ASE) at 1050 nm. We discuss ASE filtering using in-fiber Bragg gratings and present results supporting its feasibility. The article also examines thermal and viscous properties of matched core and cladding glasses in relation to preform and fiber fabrication.