A compact, mid-infrared (MIR), synchronously pumped, fiber-feedback optical parametric oscillator (OPO) based on periodically poled lithium niobate (PPLN) is developed with tunable signal and idler wavelength ranges of 1472.0-1758.2 nm and 2559.1-3562.7 nm, respectively. A solid-core SMF-28 fiber and a hollow-core fiber (HCF) were used as the feedback fibers in order to compare the effect of their substantially different levels of nonlinearity. The OPO generates 1-MHz, 120-ps, MIR pulses with up to 1.50-µJ pulse energy and 11.7-kW peak power.