No signal when connected via fiber optic cable is usually caused by physical cable issues, faulty transceivers, or router configuration errors.

Check Physical Fiber Connections

Start by inspecting the fiber optic cable for visible damage, sharp bends, or kinks, as these can interrupt signal transmission . Ensure that connectors are clean and properly seated; dust or oil on the end faces can block light signals. Use lint-free wipes and isopropyl alcohol to clean connectors if necessary . If the cable is damaged, replace it with a compatible fiber optic cable.

Verify Router and Transceiver Functionality

Check the router and any transceivers for proper operation. Look for LED indicators: a “LOS” (Loss of Signal) light or a red WAN LED signals connectivity issues . Restart the router and any connected devices to resolve temporary glitches. If possible, swap transceivers with known working units to rule out hardware failure .

Test Signal Strength

Use a fiber optic power meter or OTDR to measure signal strength. Values outside the typical range (around -15dBm to -30dBm) indicate signal loss or attenuation . For long-distance connections, consider using optical amplifiers or repeaters to boost signal quality .

Check Router Configuration

Ensure the router is receiving a valid IP address. If the router shows 0.0.0.0, it may not be communicating with the modem or ONT properly . Steps to resolve this include:

• Reboot the modem/ONT and router in the correct order.
• Verify the router's WAN port connection.
• Clone the computer's MAC address to the router if the ISP restricts access.
• Adjust the router's LAN IP address to avoid conflicts with the modem .

Environmental and Compatibility Factors

Extreme temperatures, moisture, or incompatible fiber components can also cause signal loss . Ensure that all fiber components are compatible and properly aligned, and that cables are routed to minimize stress and environmental exposure.

When to Contact Support

If the above steps do not restore connectivity, contact your ISP or equipment vendor for further assistance. They can perform advanced diagnostics, including OTDR testing, and replace faulty equipment if needed . By systematically checking physical connections, hardware, signal strength, and configuration, most fiber optic no-signal issues can be identified and resolved.