Testing fiber optic cable is essential to ensure proper performance, especially after installation or repair. There are several methods and tools for testing fiber optic cables, each suited for different aspects of the cable’s functionality, including signal strength, loss, and continuity. Here’s a step-by-step guide on how to test fiber optic cable using the most common tools:
1. Visual Inspection
Before performing technical tests, visually inspect the fiber optic cable for any physical damage, bends, or connectors that are not properly fitted.2. Optical Power Meter and Light Source
An optical power meter (OPM) and a light source are commonly used to measure the signal loss (attenuation) in a fiber optic link. This test is called an insertion loss test.Tools Required:
- Optical power meter
- Light source (laser or LED)
- Fiber optic test jumpers
Steps:
- Turn on the Light Source:
- Connect the light source to one end of the fiber optic cable.
- Connect the Power Meter:
- At the other end of the fiber, connect the optical power meter.
- Measure the Power Level:
- The power meter will measure the amount of light passing through the fiber and display the power level in dBm (decibel-milliwatts).
- Compare with Reference Values:
- Compare the measured power level with the expected value for the fiber type and length to determine signal loss.
3. Optical Time-Domain Reflectometer (OTDR)
An OTDR is used to detect faults, breaks, splices, and bends in the fiber optic cable by sending pulses of light down the fiber and measuring the reflections. It gives a detailed view of the fiber’s performance over its entire length.Tools Required:
- OTDR device
- Launch and receive cables
Steps:
- Connect the OTDR:
- Connect the fiber to be tested to the OTDR using the launch cable.
- Configure the OTDR Settings:
- Set the appropriate parameters such as wavelength, fiber length, and pulse width depending on the fiber type and application.
- Start the Test:
- The OTDR will send light pulses down the fiber and measure the reflected signal.
- Analyze the Results:
- The OTDR will display a graphical trace showing the location and extent of any faults, splices, or bends along the cable. It also shows the overall loss of the fiber.
4. Visual Fault Locator (VFL)
A VFL is a laser device used to find breaks, bends, or faulty connectors in fiber optic cables. It emits visible red light that travels through the fiber and shows where there is a fault by shining through at the break or bend.Tools Required:
- Visual fault locator
Steps:
- Connect the VFL to the Fiber:
- Attach the VFL to one end of the fiber optic cable.
- Turn on the VFL:
- The VFL will emit a visible red laser that travels through the fiber.
- Inspect for Light Leaks:
- If there is a break or sharp bend in the fiber, the red light will escape at the fault point, indicating the location of the issue.
5. Continuity Test
A continuity test checks whether the fiber optic cable is physically intact from one end to the other.Tools Required:
- Fiber optic light source
- Visual fault locator (optional)
Steps:
- Connect the Light Source:
- Attach a light source to one end of the fiber optic cable.
- Check for Light at the Other End:
- Observe whether light is visible at the opposite end of the fiber, confirming that the cable is intact.
6. Inspection and Cleaning
Dirty or damaged connectors can cause significant signal loss, so inspecting and cleaning connectors is crucial.Tools Required:
- Fiber inspection microscope
- Fiber cleaning wipes or pen
Steps:
- Inspect the Connector:
- Use a fiber inspection microscope to check the condition of the fiber connector end-face.
- Clean the Connector:
- If dirt or dust is present, clean the connector with fiber optic cleaning wipes or a fiber cleaning pen.
Summary of Fiber Optic Testing Methods:
- Optical Power Meter and Light Source: Measures signal strength and loss (attenuation).
- OTDR: Detects faults, splices, bends, and overall loss along the fiber’s length.
- Visual Fault Locator (VFL): Identifies breaks and bends in the fiber using visible light.
- Continuity Test: Checks the physical integrity of the cable.
- Inspection and Cleaning: Ensures connectors are clean and functional.