The optical properties of three-dimensionally-ordered self-assembled photonic crystals are studied in the Bragg wave coupling regime. Angle-resolved photonic stop gap measurements show the Bragg wave coupling extending over an angular range of 18°. The new diffraction peak originating at the Bragg wave coupling regime is due to the (111) stop gap. The Bragg wave coupling regime is analyzed for photonic crystals with different lattice constants and refractive index contrasts. For lower-index-contrast photonic crystals, Bragg wave coupling occurs at a lower angle of incidence as compared to higher-index-contrast photonic crystals of similar lattice constants. The exchange of energy between the diffraction peaks in the coupling regime is discussed. Experimental results are compared with theoretical calculations and they are in good agreement. Furthermore, we demonstrate tunable stop gap with high reflectance and photonic strength in the fiber-optic communication wavelength range.