We formulated a high birefringence, large dielectric anisotropy, UV stable, and low absorption loss nematic liquid crystal mixture, named UCF-15, for mid-wave infrared (MWIR) applications. To achieve fast response time, we fabricated a polymer network liquid crystal (PNLC) using UCF-15 as host. At 40°C operating temperature, our PNLC shows 2π phase change at λ = 4 μm, submillisecond response time, and over 98% transmittance in the 3.8 to 5.1 μm region. Potential applications of this PNLC phase modulator for high speed laser beam steering, adaptive optics, and optical tweezer are foreseeable.