Multi-stage ytterbium fiber-amplifier seeded by a gain-switched laser diode

TL;DR

This paper demonstrates a multi-stage fiber amplification system for 11 ps pulses from a gain-switched laser diode, achieving high gain and pulse energies with low noise, using a novel spectral density ratio method.

Contribution

It introduces a novel time-domain approach to optimize the pre-amplifier and achieves high gain and pulse energy in a fiber-amplifier system seeded by a gain-switched laser diode.

Findings

Achieved 73 dB total gain and >5.6 μJ pulse energy.

Used a novel spectral density ratio method for optimization.

Maintained a low noise figure with an 18/1 signal-to-noise PSD ratio.

Abstract

We demonstrated all-fiber amplification of 11 ps pulses from a gain-switched laser diode at 1064 nm. The diode was driven at a repetition rate of 40 MHz and delivered 13 $\mu$W of fiber-coupled average output power. For the low output pulse energy of 325 fJ we have designed a multi-stage core pumped pre-amplifier in order to keep the contribution of undesired amplified spontaneous emission as low as possible. By using a novel time-domain approach for determining the power spectral density ratio (PSD) of signal to noise, we identified the optimal working point for our pre-amplifier. After the pre-amplifier we reduced the 40 MHz repetition rate to 1 MHz using a fiber coupled pulse-picker. The final amplification was done with a cladding pumped Yb-doped large mode area fiber and a subsequent Yb-doped rod-type fiber. With our setup we reached a total gain of 73 dB, resulting in pulse energies of >5.6 $\mu$J and peak powers of >0.5 MW. The average PSD-ratio of signal to noise we determined to be 18/1 at the output of the final amplification stage.