6.5 W of average power have been generated by a mid-infrared ZnGeP<sub>2</sub> (ZGP) optical parametric oscillator (OPO)
pumped directly by a Q-switched Tm3+-doped single-oscillator fiber laser. The Tm<sup>3+</sup>-fiber pump laser based on a silica
polarization-maintaining (PM) double-clad fiber provided average powers of up to 23 W at pulse widths of 65 ns at
40 kHz repetition rate. The ZnGeP<sub>2</sub> OPO produces 45 ns mid-IR pulses. The OPO slope efficiency was 40% and the
optical-to-optical conversion efficiency 32%.
The generation of mid-infrared (mid-IR) supercontinuum (SC) radiation, ranging from 2 - 5 μm, is subject of intense research due to its wide range of applications. A very popular host media for mid-IR SC generation are soft glass fibers owing to their low-loss transmission in the mid-IR wavelength regime, particularly fluoride fibers are very attractive for high-power operation. In this research study, a diode-pumped Q-switched mode-locked (QML) thulium (Tm<sup>3+</sup>)-doped double-clad silica fiber laser is used to pump a ZrF<sub>4-</sub>BaF<sub>2-</sub>LaF<sub>3-</sub>AlF<sub>3-</sub>NaF (ZBLAN) fiber for mid-IR SC generation. The QML regime of the fiber laser is actively generated by two acousto-optic modulators. The Tm<sup>3+</sup>-fiber laser provided up to 23.5 W (26 W) of average output power in QML (continuous wave) regime with a slope efficiency of 36 % (32 %). The measured beam quality has been close to the diffraction-limit in QML regime. The system delivered mode-locked pulses with a duration of 7.5 ps, measured with a commercial autocorrelator system, at a repetition rate of 46 MHz. The Q-switched envelopes had a width between 50 and 150 ns depending on the output power level and the adjustable repetition rate. Mid-IR SC with an average output power in all spectral bands of 4.5 W have been achieved with more than 3 W/ 1.7 W/ 1 W/ 0.36 W after a long-wave-pass filter with a 3 dB-edge at 2.15 μm/ 2.65 μm/ 3.1 μm/ 3.5 μm.
This paper describes new laser sources and non linear conversion setups for 2 μm and mid-IR generation based
on fiber technologies developed at ISL. Especially for jamming heat-seeking missiles, these novel designs allow
to propose future compact, efficient and integrable laser systems. The specialty of the ISL technology lies in the
use of single 2 μm fiber laser oscillators, which deliver the full output peak power to pump optical parametric
oscillators or nonlinear fibers. No multi-stage amplifiers at 2 μm or 1.55 μm are necessary to efficiently pump
non linear converters to obtained useful energies in the mid-infrared spectral range. This technology leads to
efficient, simple and promising setups to be implemented in flying platforms. The best results achieved in continuous-wave (CW), Q-switched (QS) and mode-locked (ML) regimes with fiber lasers based on Tm<sup>3+</sup>-doped and Tm3+,Ho<sup>3+</sup>-codoped fibers are presented. Up to 70 W of average power was achieved around 2 μm with a Tm<sup>3+</sup>-doped fiber in CW regime. In ML regimes, at a repetition rate of 66 MHz, 50 W of average power was reached. In QS regime, up to 32 W of average power was generated around 2 μm with a polarization maintaining Tm<sup>3+</sup>-doped fiber at a repetition rate of 40 kHz. With a Tm<sup>3+</sup>,Ho<sup>3+</sup>-codoped fiber, up to 25 W of average power was obtained around 2070 nm in Q-switched regime. For example at 50 kHz, the pulse duration was around 50 ns at the maximum output power. The M<sup>2</sup> was estimated to be less than 1.2.
The emission from QS fiber lasers was used to directly pump OP-GaAs and ZGP OPOs. For example, in band II,
up to 6.5 W of averaged power was recently obtained from a ZGP OPO pumped by a Tm<sup>3+</sup>-doped fiber laser. At
40 kHz repetition rate, the pulse duration was around 65 ns at the maximum output power. For 3 W of averaged
output power, the M<sup>2</sup> of the signal beam was estimated to be less than 2.1 and less than 2.4 for the idler beam.
Using a mode-locked Tm<sup>3+</sup>-doped fiber laser to pump a ZBLAN fiber at an injection efficiency of ~60%, an
overall supercontinuum power of up to 2.2 W from a pump power of 5.4 W was achieved. The power above 2650 nm was 0.7 W.