What type of light source is typically used with Single-Mode Fiber?

Single-Mode Fiber (SMF) is designed to carry light directly down the fiber core, which has a very small diameter, typically around 8 to 10 micrometers. The primary characteristic of Single-Mode Fiber is that it allows only a single mode of light to propagate, reducing modal dispersion which enhances the performance over long distances.

A laser light source, particularly a laser diode, is typically used with Single-Mode Fiber because it provides a coherent and focused beam of light that can efficiently travel the long distances that SMF is designed for. The narrow spectral width of the laser light minimizes dispersion and maximizes bandwidth, making it ideal for high-speed and long-distance communications.

In contrast, Light Emitting Diodes (LEDs) are generally used with Multi-Mode Fiber due to their broader light emission and less directional output, which fits the larger core size and is suitable for shorter distances. Phototransistors and tunable lasers may have specific applications, but they are not standard sources for Single-Mode Fiber in typical networking contexts.