We present a 3.8 µm self-optical parametric oscillator (SOPO) pumped by a pulsed laser diode (LD) based on only one Nd:MgO:PPLN crystal. The problem of heat accumulation in Nd:MgO:PPLN crystals caused by high-power laser pumping is significantly optimized. The generation of non-matching polarized fundamental light is suppressed, ensuring the output of π-polarized (π-pol) 1084 nm fundamental light across the entire pumping range, and satisfying the polarization matching condition. The mid-infrared SOPO system based on this method is not only compact in structure, and stable in central wavelength, but also improves the self-conversion efficiency. Moreover, a maximum output power of 3.04 W is obtained at 3814 nm in pulse pumping mode, which represents the highest output power in 3.8 µm SOPOs. The corresponding repetition frequency is 25.11 kHz and the single pulse width is 11.45 ns.