Anisotropic photonic crystals for angle-independent light manipulation: fundamentals, design and practical implementation

One-dimensional photonic crystals (1D PhCs) are among the most fundamental building blocks of modern photonic devices owing to their simple, lithography-free architecture, ease of fabrication, and versatile optical properties. Their optical response can be reconfigured through external stimuli such as the angle of incidence, temperature, pressure, electric fields, and magnetic fields. While such tunability is advantageous for active photonic applications, uncontrolled variations can cause undesirable spectral shifts and performance degradation, creating challenges for stable device operation. This review surveys recent strategies developed to reduce the incident-angle dependence in 1D PhCs, covering their theoretical foundations, design approaches, and applications. It discusses angle-independent photonic band gaps (PBGs) and confined modes in conventional and topological 1D PhCs hybridized with anisotropic layers, with emphasis on effective medium theory and phase-compensation mechanisms. Furthermore, coupled-resonance phenomena and emerging quantum-inspired optical effects are reviewed, highlighting their underlying mechanisms and potential photonic applications. Finally, current challenges and future opportunities for robust, angle-independent photonic devices are discussed.