What is the thread inside the pigtail fiber optic cable

The thread inside a pigtail fiber optic cable is typically made of aramid yarn (Kevlar) or other strength members like fiberglass rods to provide mechanical support and protect the delicate optical fiber.

Structure of a Pigtail Fiber

A fiber optic pigtail consists of a short length of optical fiber with a factory-terminated connector on one end and a bare fiber on the other end, usually ranging from 0.5m to 5m in length . The bare fiber is designed to be fusion-spliced to a larger fiber optic cable in the field. Because the fiber itself is extremely fragile, the pigtail includes internal reinforcement to prevent breakage during handling and installation .

Strength Members

The internal thread or strength member is commonly made of aramid fibers (e.g., Kevlar), which provide high tensile strength while remaining lightweight . In some designs, fiber-reinforced plastic (FRP) rods or steel threads may also be used, especially in armored or outdoor pigtails, to enhance durability and resistance to pulling forces . These materials absorb mechanical stress, protect against micro-bending, and ensure the optical signal remains intact during installation and operation.

Protective Layers

Around the fiber and strength member, pigtails often have a tight buffer coating (typically 0.9mm diameter for indoor pigtails) and an outer jacket made of PVC or LSZH (Low Smoke Zero Halogen) for additional protection . In armored pigtails, a metallic or reinforced tube surrounds the fiber and aramid thread to provide extra protection against harsh environments .

Summary

The thread inside a pigtail fiber optic cable is not the optical fiber itself but a reinforcing material, usually aramid yarn or FRP, which ensures mechanical strength, prevents fiber breakage, and maintains signal integrity during splicing and deployment . This design allows pigtails to be safely handled, spliced, and installed in optical distribution frames, terminal boxes, or patch panels.