We report the generation of tunable mid-infrared optical pulses using all-solid-state pumped optical parametric oscillator in a periodically poled lithium niobate. Several ways were used to lower the threshold, resulting in a mean threshold as low as 6.5m W and an achievement of wavelength conversion in the 2.77-4.04μm spectral range. Continuous tuning range from 2.97 to 3.25 μm was achieved. The maximum idler output power of 466 m W at the wavelength of 3.41 μm was obtained, which represents an optical-to-optical conversion efficiency of 19%from incident pump power to the idler output.