Which light source is typically used for single-mode fiber testing?

The choice of a laser diode as the light source for single-mode fiber testing is due to its capability to produce coherent light, which is essential for effective testing of single-mode fibers. Single-mode fibers have a small core diameter, usually around 9 micrometers, and can transmit only one mode of light. This allows for long-distance signal transmission with minimal attenuation and dispersion.

A laser diode emits a narrow, focused beam of light that maintains a specific wavelength, typically around 1310 nm or 1550 nm. This coherence and the ability to operate at these standard wavelengths make laser diodes particularly suitable for testing the performance of single-mode fiber installations. The focused beam also allows for better coupling into the small core of single-mode fibers, leading to more accurate measurements of loss and signal quality.

In contrast, other options like incandescent bulbs, tungsten lights, and LEDs produce broader light spectra and are more suited for multimode fiber testing, where larger core sizes can accommodate multiple light paths. These sources would not provide the precision and efficiency needed for testing single-mode fibers, where the focus on a single light mode is crucial for accurate diagnostics and performance assessment.