Optical fiber, as the basic carrier of modern high-speed and high-capacity communication, is the key to the interconnection of the world. With the rapid development of the communications industry in recent decades, ordinary single-mode optical fiber can no longer meet the special needs of various industrial applications, so a series of optical fibers with complex internal structures, such as polarization-maintaining fibers, multi-core fibers and photonic crystal fibers, and other specialty optical fibers came into being in the civil and military fields are indispensable.