Sub-Microsecond Pulsed Pumping as a Means of Suppressing Amplified Spontaneous Emission in Tandem Pumped Fiber Amplifiers

We propose a new tandem pumping scheme in three-level rare-earth-doped optical fibers, where energy storage in a pump fiber laser enables much shorter (~500 ns) pump pulses than is possible with pulsed diode laser pumping. This has the effect of reducing the time during which the final amplifier has high inversion and, hence, reduces the amplified spontaneous emission (ASE) when compared with continuous wave (CW) tandem pumping. We simulate the gain and ASE dynamics in a pulse-pumped Yb-doped fiber amplifier and show that the ratio of amplified signal to ASE background can be improved by up to two orders of magnitude over a large range of pulse energies compared with CW tandem pumping. Sub-microsecond pulsed tandem pumping offers a relatively straightforward, as yet experimentally untried, way to substantially reduce undesirable ASE compared with the levels in diode-pumped fiber amplifiers.