Special fiber with large diameter is suitable for 850nm and 1300nm windows; low loss, high bandwidth; PCVD process ensures that the refractive index distribution is precisely controlled, heavy，Good renaturation; good mechanical properties and environmental properties. Other types of special fibers with large core diameters are shown in Table 6.1. Special optical fibers with large core diameters can be processed into various fiber end face shapes. They have many uses and are often used in short-distance communication networks, data transmission, communication equipment, and intensity-modulated optical fiber sensors.