What type of light is typically used in testing single-mode fiber?

Single-mode fiber is designed to carry light signals with minimal dispersion over long distances. This is achieved by allowing only one mode of light to propagate through the fiber at any given time. The light typically used in testing single-mode fiber is a laser light source.

Laser light provides a coherent and monochromatic output, which is essential for effective testing and measurement in single-mode fibers. The specific wavelengths used for testing, often around 1310 nm or 1550 nm, correspond to optimal transmission frequencies for single-mode fiber, enhancing accuracy in measurements such as insertion loss and back reflection.

In contrast, other light sources like LED, incandescent, and halogen generate light in a broader spectrum and are more suitable for multi-mode fibers where disperse modes can be utilized. Since they do not provide the same level of precision and focus as lasers, they aren't ideal for applications requiring the capabilities of single-mode fiber optics.