Which of the following represents a singlemode fiber size?

Singlemode fiber is characterized by its small core size, which allows only one mode of light to propagate, enabling long-distance data transmission with minimal signal loss. The standard core size for singlemode fiber is 9 microns in diameter, paired with a cladding diameter of 125 microns. This specific size is crucial for singlemode applications, as it limits the light to a single pathway, promoting the clarity and integrity of the data being transmitted over long distances.

In contrast, the other options represent multimode fiber sizes. Multimode fibers have larger core diameters (like 62.5 microns and 50 microns), which allow multiple modes of light to propagate. This can lead to modal dispersion over longer distances, making them less suitable than singlemode fibers for high-bandwidth and long-distance communications. The option with the dimensions 100/140 microns also indicates a multimode fiber, suitable for specific applications but not classified as singlemode. The distinction is essential for ensuring that fiber optics installations meet the performance requirements specific to the intended application.