Which light-emitting component the yellow or blue pigtail fiber

The yellow pigtail typically corresponds to single-mode fiber, which is used with laser light sources, while the blue pigtail indicates a UPC-polished connector rather than the fiber type itself.

Fiber Color Coding

Yellow Jacket: Signifies single-mode fiber (OS1 or OS2) with a 9 µm core, designed for long-distance, high-speed transmission using laser light sources. This is the fiber that carries the light emitted from the LED or laser in the network equipment. Blue Connector: Indicates a UPC (Ultra Physical Contact) polish on the fiber end-face, which is flat and provides low return loss.

The blue color does not indicate the fiber type but rather the connector polish type. It is compatible with single-mode fibers but is distinct from the fiber jacket color.

Practical Implications

When connecting a light-emitting component, such as a pigtailed LED or laser, to a fiber optic network, the yellow pigtail is the one that carries the light through the single-mode fiber. The blue connector ensures proper mating with other UPC-polished connectors, maintaining low back reflection and signal integrity. Misconnecting fibers with different colors or polish types (e.g., APC green to UPC blue) can damage the fiber or degrade performance.

Summary

For light transmission in a fiber optic system: Yellow pigtail = single-mode fiber, carries the light from the source. Blue pigtail = indicates UPC connector polish, not the fiber type itself. Thus, the yellow pigtail is the light-emitting component in terms of the fiber that transmits the optical signal, while the blue color is relevant for connector type and compatibility.