Layer-by-layer three-dimensional photonic crystals are fabricated by low-temperature atomic layer deposition of titanium dioxide on a polymer template created by soft lithography. With a highly conformal layer of titanium dioxide, a significantly enhanced photonic band gap effect appears at 3.1μm in transmittance and reflectance. From optical investigations of systematically shifted structures, the robust nature of the photonic band gap with respect to structural fluctuations is confirmed experimentally. With angle-resolved Fourier-transform spectroscopy, the authors also demonstrate that the fabricatedphotonic crystal can be a diffraction-free device as the photonic band gap exists over the diffracting regime.