In insertion loss testing, which setup is used to measure loss by comparing input and output power?

• A. Optical Loss Test Set
• B. Visual Fault Locator
• C. Optical Time Domain Reflectometer
• D. Tracer

Answer: (A)

Insertion loss is found by comparing the light power before a device or fiber section to the power after it. You need a setup that provides a known input power and measures the output power so you can compute the loss in decibels. The Optical Loss Test Set is designed for this purpose: it combines a calibrated light source with a power meter so you can directly measure Pin and Pout and calculate the insertion loss from their difference.

The other tools serve different goals. A Visual Fault Locator is for locating faults by injecting visible light to see where a break or bend occurs, not for quantifying end-to-end loss. An Optical Time Domain Reflectometer sends pulses and maps reflections to show where losses occur along the length, giving distributed loss and fault locations rather than a single end-to-end loss value. A Tracer is used to identify cables or trace routes rather than measure insertion loss.