Hybrid fiber laser integrating fast and slow active media for accurate synthesis of high-energy arbitrary optical waveforms by cavity dumping

We demonstrate the possibility of the accurate direct laser synthesis of high-energy arbitrary optical waveforms by the programmable driving of partial cavity dumping in a specific continuous-wave fiber laser. To this effect we have developed an original hybrid laser configuration which integrates two different active media. The first medium, a semiconductor optical amplifier (SOA), acts as a saturated lumped preamplifier. It features a relatively fast (sub-nanosecond) gain recovery, and thus effectively suppresses the intracavity power fluctuations induced by cavity dumping. The second active medium, an erbium-doped fiber amplifier (EDFA), acts mainly as a booster amplifier. This distributed inertial amplifying medium effectively accumulates pump energy, thereby providing an enhancement of output energy upon cavity dumping. Our simple proof-of-concept laser setup has allowed the synthesis of nanosecond arbitrary optical waveforms with an energy up to 40 nJ and arbitrarily tunable repetition rate. The proposed combination of a slow (EDFA) and fast (SOA) amplifying stages prevents the laser from strong relaxation oscillations and power flux fluctuations which essentially restrict cavity dumping in conventional rare-earth-doped fiber lasers. The applied two-stage intracavity spectral filtering ensures spectral purity of a rather narrowband (<= 0.1 nm) laser output. For the purpose considered, the integrated SOA-EDFA laser configuration is preferable to a conventional architecture 'master oscillator-power amplifier' whose nonlinear gain can obstruct the accurate synthesis of high-energy optical waveforms.