Here recent advances in photonic crystals based on silicon are reviewed. Laterally structured porous silicon with a defect line. The authors demonstrate a programmable topological photonic chip with large-scale integration of silicon photonic nanocircuits and microresonators that can be rapidly reprogrammed to implement diverse multifunctionalities. A scalar scheme has been proposed to design photonic crystals that possess. Part of the book series: Topics in Applied Physics ( (TAP,volume 94)) We introduce the concept of silicon-based photonic crystals with the main focus on the macroporous silicon material system. Due to their periodic modulation.