Overview of Common Outdoor Optical Cables
As vital carriers for information transmission, outdoor optical cables play a critical role across diverse application scenarios. They are primarily categorized into two types: central tube-type cables and layer-stranded cables. These two structures exhibit distinct performance characteristics and are suited for different environments and requirements.
Central Tube-Type Optical Cables
Tube Material and Structure
The tube of central tube-type cables is made from PBT material, which combines rigidity with flexibility to effectively resist lateral pressure. However, some smaller manufacturers may opt for lower-cost PP material as a substitute for PBT, potentially compromising fiber protection during transportation and installation. PP material appears semi-translucent, visually distinct from PBT material.
Fiber Coloring and Color-Lock Technology
In telecommunications engineering, colored plastic is extruded onto each fiber within the cable to distinguish individual cores. This coloring technique involves applying distinct ink colors to each bare fiber core in outdoor cables, totaling 12 colors arranged according to the Ministry of Information Industry's industry standard color spectrum. Additionally, to further protect the fibers, their surfaces are coated with a 250-micron layer of translucent resin. This color-locking fiber technology is employed in certain foreign fiber production processes. While it eliminates the coloring step, it may limit flexibility during fiber distribution.
Water-Blocking Tape and Non-Woven Fabric
The water-blocking tape is a critical component in optical cable construction, consisting of two layers of non-woven fabric sandwiching water-absorbing powder. Upon cable water ingress, the powder rapidly absorbs moisture and expands, forming a gel-like substance that effectively prevents further water penetration into the cable. However, some manufacturers may substitute the water-blocking tape with lower-cost non-woven fabric to reduce expenses. Such substitutes fail to provide effective water blocking when the cable outer sheath is damaged.
Reinforcement Components and Other Materials
Optical cables incorporate corrugated steel tape, primarily to enhance lateral pressure resistance and tensile strength while preventing rodent damage and protecting the tube bundle. Additionally, two parallel steel wires reinforce the cable's tensile strength. These wires undergo specialized treatments like phosphating or galvanizing to prevent rust.
Sheath Materials and Cost Considerations
Outdoor cables typically employ medium-density polyethylene (MDPE) as the sheath material, though some customers may specify high-density polyethylene (HDPE). While HDPE increases costs, it offers superior physical properties. Some orders may also require low-smoke, zero-halogen (LSZH) materials for the sheath. However, to reduce costs, certain manufacturers may opt to use recycled materials for the cable sheath. While this reduces expenses, it may lead to issues such as inconsistent quality, rough surface texture, impurity contamination, and susceptibility to cracking and water ingress.
Layered-Stranded Optical Cable
Layered-Stranded Optical Cable Structure
Layered-stranded optical cables achieve enhanced strength and water/moisture resistance by tightly braiding multiple fiber-filled tubes around a central strength member. Common types include GYTS and GYTA. This structure allows flexible combination of loose tubes to produce cables with numerous fiber counts.
GYTA vs. GYTS Comparison
GYTA and GYTS are two common stranded optical cables. The GYTS structure features multiple tubes twisted around a thicker phosphated steel wire, with water-blocking cable compound filling the gaps in the twisted cable. GYTA cables use aluminum tape instead of steel tape. While potentially slightly inferior in lateral pressure resistance, they offer superior rustproofing and moisture barrier performance, making them suitable for conduit environments.
GYFTY Optical Cable
The GYFTY cable is characterized by its reinforcement and waterproofing capabilities. Its specialized stranding design and cable compound filling make it suitable for diverse environments such as aerial and direct burial applications. To enhance tensile strength in aerial installations, manufacturers incorporate aramid fibers around the stranded core.
Other Layer-Twisted Structures
Additional layer-twisted cable configurations include ADSS and OPGW types. ADSS cables incorporate an outer aramid layer covered by a sheath, while OPGW cables house fibers within aluminum tubes. These tubes are twisted with steel wires to form a robust all-metal structure, emphasizing lightning protection capabilities.