Integration of photonic crystals with terahertz for next-generation analytical imaging and biosensing: A review.

Photonic crystals (PCs), which are periodic dielectric structures that control light propagation, represent a transformative approach for overcoming long-standing challenges in terahertz (THz) technology. Although the THz spectrum (0.1-10 THz) offers unique advantages for spectroscopy, imaging, and biosensing through non-ionizing radiation and molecular sensitivity, its practical implementation has been hindered by difficulties in THz generation and manipulation. Recent advances in PC-based THz waveguides, filters, and sensors have demonstrated how tailored photonic bandgaps can dramatically enhance the efficiency and sensitivity of devices while enabling miniaturization. This review synthesizes the progress in photonic crystal-THz (PC-THz) integration, highlighting emerging innovations, including graphene-based PCs, metamaterial-enhanced devices, and THz fibers. By systematically addressing fabrication precision, loss mechanisms, and scalability challenges, and critically assessing water absorption limitations in biosensing, PC-THz platforms are poised to enable next-generation high-resolution imaging, real-time biosensing, and ultrafast communication systems.