Microstructure optical fiber (MOF) offers a wide range of applications in short-distance communication systems, fiber lasers, supercontinuum generation, sensors, modulators and wavelength converters, as well as in various scientific fields such as optics, electronics, medicine, biology and environmental science. Conventional step-index fibers suffer from the constraints of the monotonic structure construction and material properties, which limits the further optimization of their optical performance in terms of work bandwidth, dispersion and loss. For practical purposes such as high-capacity transmission and high-power lasers, they face the challenges such as maintaining single-mode operation with a small core size, ensuring a low cutoff wavelength and matching the thermal characteristics of the core and cladding materials. In contrast, MOF, such as the well-known photonic crystal fiber (PCF), exhibit a strong dependence of the effective refractive index of the cladding on the structural parameters and wavelength, which enables a broad tunability of the effective refractive index contrast (0 ~ 90%) between the core and cladding modes. Therefore, by adjusting the structural parameters of the fiber, such as the size, shape and lattice constant of the air holes, the fundamental mode propagation constant will be effectively controlled, easily achieving single-mode transmission with zero cutoff wavelength, high numerical aperture, ultra-flat dispersion, low loss or high nonlinearity coefficient, among other desirable fiber features. These features endow PCF with an unparalleled advantage over traditional fiber.