Mode Field Diameter (MFD) is a parameter used to characterize the spatial distribution of light modes in optical fibers. In fiber optics, a mode refers to the specific pattern of light propagating through the fiber.
MFD is particularly important in the field of optical fibers, where different modes can propagate through the fiber, each with its own unique spatial distribution. MFD is often used to describe the size of the fundamental mode (lowest order mode) in single-mode fiber or the size of a specific mode in multimode fiber.
For single-mode fiber, MFD is usually defined as the diameter of the circular area where the optical power is concentrated to a certain percentage of the total power. The most common definition is the diameter at which optical power drops to 1/e² (approximately 13.5%) of its maximum value.
In the case of multimode fiber, there can be multiple modes with different mfds. Each mode has a different spatial distribution, and MFD helps characterize the size of these modes.
Mode field diameter is a key parameter in the design and optimization of optical communication systems. It affects the modal dispersion, coupling efficiency and overall performance of the system. When selecting fiber for a specific application, ensuring that the fiber can effectively support the required modes and performance requirements is an important consideration.