Early optical fiber technology was not perfect yet. The coating on the surface of the optical fiber still used heat-cured silicone resin. The fragility of the optical fiber made the protection of the optical cable more important, and the control during the cable formation was also higher. At that time, Optical fibers are more sensitive to side pressure, -OH, and bending. Therefore, a skeleton-type single-helical twisted optical cable with complex technology was developed. The bare fiber was placed in the S-twisted U-shaped skeleton slot, and the single-fiber skeleton was developed into a multi-fiber skeleton. , using chromatographic differentiation technology to distinguish optical fibers in the same skeleton slot.
The structure of the optical cable is shown in the figure below: 
