Highly doped phosphate glass fibers for fiber lasers and amplifiers with applications

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Rare-earth doped fiber lasers and fiber amplifiers are highly attractive due to their efficiency, compactness, and, particularly, for their potential to various applications including communication systems, biomedical equipment, materials processing, LIDAR, and fiber-optic sensing. At the heart of these devices is the active fiber - most commonly based on silica host glass. However, the ability to dope silica glass fibers with high concentrations of erbium is limited due to clustering and nonlinear up-conversion - both of which degrade the efficiency of the gain fiber. Over many years, we have focused on developing highly doped phosphate glass fibers. The erbium concentrations can reach 4-5% weight erbium concentration without any negative effect to the optical gain. As a result, highly erbium doped phosphate glass fibers can produce large gain per unit length (typically 5 dB/cm) [1, 2]. This characteristic is a key enabler for a variety of optical devices that can make use of high optical gain in a short length - most notably high power single frequency fiber lasers and short length fiber amplifiers. In this presentation, we focus on two applications of the highly doped phosphate fiber. One is a high power, narrow linewidth single frequency fiber laser. The second is a fiber amplifier for coherent LIDAR applications capable of power scaling transform limited pulses without deleterious nonlinear effects. Both are examples of how this type of active fiber can lead to unique and superior performance.