Optical parametric oscillator based on periodically polled MgO:LiNbO3 pumped by repetitively-pulsed Tm3+:Lu2O3 ceramic laser with a fiber-laser pumping was experimentally studied. The average power at the spectral range of 3.7-4.2 mm at the OPO output was 530 mW at the power of 7.9 W of the ceramic laser. The full efficiency of energy conversion from NIR-IR to MID-IR was 6.7% and differential efficiency was 8%. For parametric conversion of two-micron radiation from lasers (for example, on Tm3+:Lu2O3 ceramics or Ho3+:YAG crystals) into the mid-IR range, KTP and KTA crystals with regular domain structures are also promising.