Cutoff wavelength is the wavelength at which a single-mode fiber ceases to support two modes of transmission and becomes a single-mode fiber. It is the shortest wavelength at which a single-mode fiber can carry more than one mode.
A single-mode fiber is a type of optical fiber that is designed to carry light along its length in a single mode or path. This means the light will remain confined in the fiber core, propagating in a single direction with a narrow beam of light. This is in contrast to a multi-mode fiber, which allows the light to travel in multiple paths or modes.
The cutoff wavelength of a single-mode fiber is the wavelength at which the fiber can no longer support two modes of transmission. This occurs because the higher wavelengths become too large to remain confined within the fiber core and will escape into the cladding. As a result, only one mode of transmission will be supported by the fiber.
The cutoff wavelength of a single-mode fiber is important because it determines the upper limit of the wavelength a fiber can support. It is also used to determine the type of fiber used in a particular application. For example, a fiber with a cutoff wavelength of 850 nanometers (nm) is typically used for short distance applications, while a fiber with a cutoff wavelength of 1310 nm is better suited for long distance applications.
In summary, the cutoff wavelength of a single-mode fiber is the shortest wavelength at which the fiber can support more than one mode of transmission. It is important for determining the type of fiber used for a particular application, and for setting the upper limit of the wavelength the fiber can support.