The mode-order conversion characteristics of a heterostructure formed by regular photonic crystals (PCs) with high symmetry and PCs with low symmetry are analyzed numerically. The working principle of the proposed mode-order converter is based on the phase retardation of the incident beam while propagating through the PC heterostructure. This type of phase delay arises from the effective refractive index difference between the symmetrical PC and the asymmetric PC, called a modified annular PC (MAPC), at the specified frequency regimes α/λ = 0.281-0.34. Further optimizations that are carried out improve the mode-order conversion bandwidth, reaching up to 24%. By means of such a novel-type configuration, a propagating fundamental mode can be transformed into higher-order modes at the output with adequate transmission efficiency. © 2013 Optical Society of America.