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

Abstract

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 3+ -doped and Tm 3+ ,Ho 3+ -codoped fibers are presented. Up to 70 W of average power was achieved around 2 µm with a Tm 3+ -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 3+ -doped fiber at a repetition rate of 40 kHz. With a Tm 3+ ,Ho 3+ -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 M² 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 3+ -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 M² 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 3+ -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.