High-power Nd-doped double-clad fiber amplifier at 1.06 μm

Abstract

In this study, we clarify the performance of a Nd-doped fiber amplifier (NDFA) at 1.06 micrometer as a booster amplifier and a preamplifier. As a booster amplifier, we propose a Nd-doped double-clad fiber (DCF) amplifier. The DCF configuration could be the most promising technique for obtaining high output power from the NDFA, because of its potentially low amplifying threshold characteristics in an ideal four-state system, and the easy pump lightwave coupling to a broader first cladding area in the DCF. The proposed DCF is spliced with a normal single mode fiber at one end of the DCF as a signal input port, to avoid multi-mode propagation of the input signal lightwave through the first cladding area. Design parameters, such as the length and Nd concentration of the DCF, will be optimized by further study. The theoretical result predicts a 2-watt signal output power by a 10-watt pump power coupling to the DCF. For comparison, a booster amplifier employing four-LDs pump scheme is also demonstrated. As a preamplifier, we clarify the NDFA's high-sensitivity performance in giga-bit transmission. The NDFA will provide high-power, low-noise, robust, multigigabit optical transmitters and receivers for free-space laser communications systems.