Alkaline-free phosphate glasses for ultra compact optical fiber amplifiers at 1.5 μm

New alkaline-free phosphate glass compositions are presented. A phosphate glass with a temperature coefficient of refractive index close to zero and a good chemical durability can be achieved. These new glass compositions are very promising for high quality optical fibers with a constant mode profile, and erbium-doped fiber amplifiers with a high gain per unit length.