High-power sensitised erbium optical fibre amplifier

Abstract

Much of the recent discussion regarding the systems deployment of erbium-doped fiber optical amplifiers has focussed on the pump source. Ideally, when choosing which pump band to use, one desires high efficiency, quantum limited noise performance, and the availability of a long-lived semiconductor based pump source. Initial experiments focussed on the 800 nm pump band of erbium due to its coincidence with commercially-available high-power AlGaAs diode lasers. Unfortunately, the presence of a strong excited state absorption (ESA) in this pump band severely limits the gain performance and degrades the amplifier noise figure. The pump wavelengths of 980 and 1480 nm have their advantages and disadvantages with regards to gain efficiency, amplifier noise figure and overall system advantages. However, there still remain questions with regard to pump laser reliability at both of these wavelengths. We describe here the operation of the sensitized erbium (Er³⁺/Yb³⁺) optical amplifier using a diode-pumped Nd³⁺ laser (DPL) as the pump source at 1064 nm. This approach indirectly utilizes highly non-diffraction limited high-power AlGaAs diode laser arrays and is easily power scalable, a notable advantage for a power optical amplifier. This pumping scheme operates without any noticeable ESA and exhibits a near quantum-limited noise figure. Previous work has focussed on the use of frequency-doubled DPL's at 532 nm as a pump source for erbium fiber amplifiers. In terms of overall efficiency, the utilization of the Nd³⁺ DPL fundamental as the pump source is a significant improvement and avoids the operational complexities of the nonlinear frequency-doubling process.

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