Running fiber optic cable underground involves several key steps, including planning, trenching, cable laying, splicing, and testing.
1. Planning and Designing the Network
Before any digging begins, careful planning is essential. This includes:
- Network Layout: Determining the optimal route for the fiber optic cable, considering distance, obstacles (like existing utilities), and accessibility. This should be documented in detailed plans.
- Permits and Approvals: Obtaining necessary permits from local authorities and utility companies. This often involves submitting plans and agreeing to specific regulations.
- Utility Locating: Identifying and marking existing underground utilities (gas, water, electricity) to avoid damage during excavation. One-Call services (like 811 in the US) are crucial for this step.
- Environmental Considerations: Assessing potential environmental impacts and implementing mitigation strategies.
2. Trenching and Conduit Placement
This stage involves creating a pathway for the fiber optic cable.
- Trenching: Digging a narrow trench along the planned route. The depth of the trench depends on local regulations and soil conditions, but it's typically between 24 and 48 inches.
- Conduit Installation (Recommended): Placing a protective conduit (duct) inside the trench. Conduit is often made of PVC or HDPE and protects the fiber optic cable from damage from soil, water, and rodents. It also simplifies future repairs or upgrades.
- Direct Burial (Less Common): In some cases, the fiber optic cable can be directly buried without conduit. This is generally less expensive but offers less protection and makes future maintenance more difficult. Specialized direct burial cable with extra layers of armor is required.
- Backfilling: After the conduit (or cable in direct burial applications) is in place, the trench is backfilled with soil, ensuring proper compaction to prevent settling. Warning tape is often placed above the conduit before backfilling to alert future excavators.
3. Cable Laying and Protection
This is where the fiber optic cable is installed within the conduit or directly into the trench.
- Cable Pulling/Blowing: Fiber optic cable is carefully pulled or blown through the conduit using specialized equipment. Lubricants are used to reduce friction. Blowing uses compressed air to propel the cable through long conduit runs.
- Slack Loops: Leaving slack loops of cable at regular intervals or in handholes. This allows for future repairs or rerouting without stressing the cable.
- Avoiding Sharp Bends: Ensuring that the cable is not bent beyond its minimum bend radius, as this can damage the fibers and degrade signal quality.
4. Splicing, Termination, and Conduit Utilization
Connecting the fiber optic cable to equipment and using the conduit system effectively.
- Splicing: Joining two fiber optic cables together, usually in a splice enclosure. This is done using specialized splicing equipment that precisely aligns the fibers and fuses them together.
- Termination: Connecting the fiber optic cable to network equipment using connectors. Connectors are attached to the ends of the fibers and plugged into optical transceivers.
- Handholes/Manholes: Strategically placed handholes or manholes allow access to the conduit system for maintenance, repairs, and future expansion.
5. Testing and Verification
Ensuring the fiber optic network is working correctly.
- Optical Time Domain Reflectometer (OTDR) Testing: Using an OTDR to measure the length of the fiber, identify any breaks or imperfections, and assess signal loss.
- Power Meter Testing: Measuring the optical power at the receiver end to ensure it meets the required specifications.
- Documentation: Maintaining detailed records of the network layout, cable routes, splice locations, and test results.
In summary, running fiber optic cable underground is a multi-stage process requiring meticulous planning, careful execution, and thorough testing to ensure a reliable and long-lasting network.
