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How is Fiber Light Measured?

Published in Fiber Optics 3 mins read

Fiber light is typically measured by determining the optical power level at the receiving end of the fiber after injecting a known amount of light at the transmitting end. The difference between these power levels represents the optical loss.

Here's a breakdown of the process:

  • Optical Loss Measurement: The most accurate way to measure the overall optical loss in a fiber is by injecting a known level of light at one end and measuring the level of light at the other end.

  • OLTS (Optical Loss Test Set): This instrument is specifically designed for this purpose. An OLTS consists of a light source and a power meter.

    • The light source injects a stable and calibrated optical signal into the fiber.
    • The power meter measures the optical power level at the receiving end.

  • Calculating Optical Loss: The difference between the injected power (source power) and the received power is the optical loss, usually expressed in decibels (dB). The formula is:

    Optical Loss (dB) = 10 * log10 (Pout / Pin)

    Where:

    • Pout is the power at the output (receiving end).
    • Pin is the power at the input (transmitting end).

  • Factors Affecting Optical Loss: Various factors contribute to optical loss in fiber, including:

    • Absorption: Intrinsic properties of the fiber material absorb some of the light.
    • Scattering: Light can be scattered by imperfections in the fiber.
    • Bending Losses: Sharp bends in the fiber can cause light to leak out.
    • Connector and Splice Losses: Connections between fibers introduce loss.

  • Importance of Measurement: Accurate measurement of optical loss is crucial for:

    • Ensuring Proper Network Performance: Too much loss can degrade signal quality.
    • Troubleshooting Network Issues: High loss can indicate a problem with the fiber or connectors.
    • Verifying Installation Quality: Measurements confirm that the fiber was installed correctly.

  • OTDR (Optical Time Domain Reflectometer): While an OLTS measures overall loss, an OTDR provides a more detailed view. It sends a pulse of light into the fiber and analyzes the backscattered and reflected light to identify the location and magnitude of losses along the fiber's length, including breaks, splices, and connectors.

In summary, fiber light is measured by injecting a known amount of light and then measuring the power at the other end of the fiber using an OLTS. The difference is the optical loss, a key parameter for assessing the quality and performance of the fiber optic link.

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