Photonic Crystal Fiber is a novel microstructured optical fiber based on the photonic bandgap effect or an enhanced total internal reflection principle. Its cladding region features periodically arranged micro air holes, and by controlling the size, spacing, and arrangement of these holes, it enables flexible dispersion management, endless single-mode transmission, high nonlinearity, and controllable birefringence—capabilities difficult to achieve with conventional fibers. This unique structure makes it an ideal medium for light transmission in advanced applications such as supercontinuum generation, nonlinear frequency conversion, and precision fiber-optic sensing.