2 μm and mid-IR fiber-laser-based sources for OCM

This paper describes new laser sources and non linear conversion setups for 2 mu m 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 mu m fiber laser oscillators, which deliver the full output peak power to pump optical parametric oscillators or nonlinear fibers. No multi-stage amplifiers at 2 mu m or 1.55 mu m 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 Tm3+-doped and Tm3+, Ho3+-codoped fibers are presented. Up to 70 W of average power was achieved around 2 mu m with a Tm3+-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 mu m with a polarization maintaining Tm3+-doped fiber at a repetition rate of 40 kHz. With a Tm3+, Ho3+-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-2 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 Tm3+-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-2 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 Tm3+-doped fiber laser to pump a ZBLAN fiber at an injection efficiency of similar to 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.