How to use a red light pen on an lc-to-lc fiber optic patch cord

A red light pen (Visual Fault Locator) can be used on an LC-to-LC fiber patch cord to check connectivity, locate breaks or bends, and verify polarity by injecting visible red light through the fiber.

Step-by-Step Guide

1. Prepare the Fiber and Pen

• Ensure the LC-to-LC patch cord is clean; wipe the LC connectors with a fiber cleaning tool to remove dust or debris .
• Remove the dust caps from both ends of the patch cord and from the red light pen's output port .
• If your VFL requires an LC adapter (1.25mm), attach it to the pen to match the LC connector . 2. Connect the Red Light Pen
• Insert the LC connector of the patch cord into the LC adapter on the red light pen securely .
• Make sure the connection is snug but do not force it to avoid damaging the ferrule. 3. Power On and Select Mode
• Turn on the red light pen. Most pens have two modes:
  • Continuous mode: emits steady red light to check end-to-end connectivity .
  • Flashing mode: helps locate faults, bends, or breaks along the fiber .
• Choose the mode depending on whether you are testing connectivity or locating faults. 4. Observe the Light
• Look at the opposite end of the LC patch cord. If the fiber is intact, red light should be visible at the far connector .
• If the light leaks out along the fiber or is dim, this indicates a break, bend, or poor splice .
• For polarity verification, ensure the light exits the expected Rx port; if it appears in the wrong location, the fiber may be reversed or crossed . 5. Troubleshooting
• If no light is visible, check the battery of the pen, the cleanliness of connectors, and the proper seating of the LC adapter .
• Avoid looking directly into the laser output to prevent eye injury. 6. After Testing
• Turn off the pen and remove the LC adapter.
• Replace dust caps on both the patch cord and the pen to prevent contamination .
• Remove the battery if the pen will not be used for a long period to prevent leakage . Using a red light pen on an LC-to-LC patch cord is a simple yet effective way to verify fiber continuity, detect faults, and ensure proper polarity in fiber optic networks. Proper cleaning, correct adapter use, and careful observation of the red light are key to accurate testing.