How to check the lights on a fiber-optic dual-electrical switch

You can check the lights on a fiber-optic dual switch by observing the TX/RX indicators, using an optical power meter, or employing a Visual Fault Locator (VFL) to verify signal transmission.

Visual Inspection of Switch LEDs

Most fiber-optic dual switches, such as the Ocean Optics FOS-2x2-TTL, have front-panel LEDs indicating the status of each channel. Typically:

• High/Low or Open/Closed positions on the switch correspond to the operational state of each channel (left/right) and may illuminate when active .
• Ensure the power supply is connected and the switch is in the correct operating mode.
• Check that the SMA fiber connectors are properly seated and the shutter switch is in the OPEN position to allow light transmission .

Using TX/RX Power Levels

For switches integrated with SFP or similar transceivers:

• TX (Transmit) Power shows the light leaving the module.
• RX (Receive) Power shows the light arriving from the remote end.
• These values are measured in dBm and can be checked via the switch CLI if the module supports Digital Optical Monitoring (DOM). For example, on Cisco devices, the command show interface transceiver details displays TX/RX levels and thresholds .
• A healthy connection typically shows TX and RX within the acceptable range; very negative dBm values indicate weak or missing signals .

Using a Visual Fault Locator (VFL)

A VFL is a simple tool to verify fiber continuity:

• Connect the VFL to one end of the fiber and turn it on.
• Observe the other end for visible red light (usually 650 nm wavelength). Light indicates the fiber is transmitting correctly .
• Areas where light leaks or fades may indicate breaks, bends, or poor splices.
• This method is effective for quick troubleshooting without requiring powered equipment at the far end .

Using an Optical Power Meter

For precise measurement:

• Connect the optical power meter to the output of the switch.
• Measure the optical power to ensure it matches the expected range for your fiber type and transceiver.
• Adjust the SMA connectors or focal points if necessary to optimize signal strength .

Safety Considerations

• Avoid direct eye exposure to fiber-optic lasers; even low-power SFPs can cause eye damage .
• Always handle fibers in a clean environment and inspect connectors for damage before testing . By combining LED observation, TX/RX monitoring, VFL testing, and optical power measurement, you can effectively check the lights and ensure proper operation of a fiber-optic dual-electrical switch.