What does "mode field diameter" refer to in single-mode fiber?

The term "mode field diameter" specifically refers to the effective diameter of the light-carrying mode in a single-mode fiber. This diameter describes the extent of the electromagnetic field in a single-mode fiber and indicates how much of the light is contained within the core of the fiber. It is a crucial parameter because it influences how the fiber performs in terms of light propagation, loss, and sensitivity to bending. A larger mode field diameter can result in lower splice and connector losses and can improve the fiber's performance when dealing with various types of light sources.

Understanding mode field diameter is important for applications that require precise control over light transmission, such as telecommunications and data networks. The other options, while related to different aspects of fiber optics, do not define mode field diameter. For instance, the total diameter of the fiber encompasses the core and the cladding, while the outer protective layer refers to the fiber's buffer or jacket, neither of which pertains to the specific characteristics of the light mode itself. The diameter of the cladding highlights the part of the fiber that surrounds the core and is designed for reflecting light back into the core but is not indicative of the mode field's characteristics. This distinction is fundamental for understanding how single-mode fibers operate effectively in various applications