No light is on the router s fiber optic cable

No light on a fiber optic cable usually indicates a power issue, a disconnected or damaged cable, or a faulty transceiver/ONT.

Check Power and Connections

First, ensure the router or Optical Network Terminal (ONT) is powered on. Verify that the power cable is securely connected at both ends and that the outlet is functioning, for example by testing with a night light or another device. Confirm the power button on the device is pressed in and not popped out.

Next, inspect the fiber optic cable itself. Make sure the cable is fully seated in both the ONT and the wall port or clamshell connector. You should hear a click when it is properly inserted.

Look for visible damage such as kinks, pinches, or pet bites. If the cable has a yellow patch with green tips, ensure it is connected correctly.

Inspect Indicator Lights

Check the ONT or router lights: Power light off: indicates a power issue.

LO

S (Loss of Signal) or Optical light off: indicates the fiber signal is not being received. Red or blinking lights: may indicate a fiber issue or low signal strength.

Test and Clean Components

If the power and connections are fine, clean the fiber connectors using lint-free wipes and isopropyl alcohol to remove dust or oil. Loose or dirty connectors can prevent the light from appearing. If available, use a power meter, OTDR, or Visual Fault Locator to test signal strength and locate breaks in the fiber.

Swap or Restart Hardware

Try restarting the router or ONT to resolve temporary glitches. If the problem persists, swap the transceiver or router with a known working unit to rule out hardware failure. When to Contact a TechnicianIf after checking power, connections, cleaning, and testing the fiber there is still no light, the issue may be a severed fiber, faulty transceiver, or ONT problem.

At this point, contact your service provider to dispatch a technician for repair. Provide them with details of the troubleshooting steps you have already performed to expedite resolution.