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

Abstract

Abstract-We propose a new tandem pumping scheme in threelevel 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 ASE when compared to continuous wave (c.w.) 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 2 orders of magnitude over a large range of pulse energies compared to c.w. tandem pumping. Sub-microsecond pulsed tandem pumping offers a relatively straightforward, as yet experimentally untried, way to substantially reduce undesirable ASE compared to the levels in diode-pumped fiber amplifiers.

Overlapped Pulsed Pumping of Tandem Pumped Fiber Amplifiers to Increase Achievable Pulse Energy

“…[11], we simulated a 14 µm core fiber (effective area (Aeff) of 130 µm 2 ) with a single transverse mode (LP01) and Ytterbium doping concentration of 4.4x10 26 /m 3 . A value for background loss typical of a commercial fiber was chosen (10 dB/km) and the strength of the back-scattering (4x10 -3 dB/km) was based on our measured values for fibers of similar composition.…”

“…systems based on Yb-fiber amplifiers has been that Overlapped pulsed pumping of tandem pumped fiber amplifiers to increase achievable pulse energy Andrew Malinowski, Jonathan H. V. Price and Michalis N. Zervas, Member, IEEE F the in-band absorption cross-sections in the 1010-1030 nm range are lower than at the 975 nm absorption peak and so efficient pump-absorption requires that the device length is increased, leading to limiting nonlinear effects. However, it has been demonstrated that converting the output of lowbrightness multimode diodes using a fiber laser to create a single mode pump source would enable core-pumping of the final tandem pumped amplifier and then increased pump absorption enables device lengths of ~2-3 m [11]. Pulsed operation typically produces higher ASE than in c.w.…”

“…In our previous paper we described how the use of a pulsed pump for tandem pumping suppresses ASE by up to 20 dB by reducing the time over which the Yb ions are highly inverted [11]. In that paper both the pump laser and the signal amplifier fiber were used for energy storage.…”

“…We used the same signal-fiber parameters as previously because they relate to widely used large-mode-area few-moded fiber designs and because this enables direct comparison of achievable energies with the previous results. (The pump and signal wavelengths are the same as in our previous paper to enable such comparison [11]. )…”

Pulsed fiber laser at 1 μm wavelength region

“…This indicates that the laser system needs to be pumped with more PP which results in higher cost. However, when operating at low pulse repetition rate with low duty cycle, the commercial 9-xx nm pump laser diodes can operate at 5~7 times higher output power than in CW mode [123]. This can be utilized to offset some of concern on the cost.…”