Modifying the symmetry of colloidal photonic crystals: a way towards complete photonic bandgap

Colloidal photonic crystals (CPCs) are a type of photonic crystals that are made of periodically arranged submicron spheres. Because of the unique advantages of cost-effectiveness, easiness and relatively large scalability for their fabrication, they have attracted a great deal of research interest for a wide range of applications. However, most of the CPCs are made of spherical building blocks with face-centred-cubic lattice, which bears only a pseudo photonic bandgap between the second and third bands. Theoretical simulation has suggested that lowering the symmetry of the building blocks or the dielectrics of the materials can potentially open a full bandgap, namely, the complete photonic bandgap. In this paper, recent efforts towards this end were thoroughly reviewed and summarised from three aspects: the symmetries of the building blocks, the crystalline lattices and the dielectrics of materials. In the end, a conclusion was given to the recent research in this field and related challenges were outlined. A promising outlook was proposed for the future direction along with its impact to the scientific community.