Single-mode is a type of optical fiber that supports the transmission of a single mode of light. It is designed to provide the most efficient means of transmitting light signals over long distances with minimal losses. This type of fiber is used in areas that require long-distance, high-speed communications such as in telecommunications and data networks.
Single-mode fiber is composed of a core, which is a glass or plastic fiber with a diameter of typically 8 to 10 microns, surrounded by a cladding layer. The core is much smaller than the cladding, which is usually 125 microns in diameter. This core-to-cladding ratio allows for light to be propagated through the fiber in one mode, rather than multiple modes which would lead to higher losses.
The single-mode fiber is designed to transmit light with a specific wavelength, which is usually 1310 or 1550 nanometers. This wavelength is referred to as the cutoff wavelength, which is the point at which the light is no longer able to travel through the fiber. Above the cutoff wavelength, only one mode of light propagation is possible. This single-mode transmission requires fewer repeaters than multimode transmission, making it more efficient.
In order for the single-mode fiber to be effective, the core and cladding must have a refractive index difference of at least 1.6%. This allows for the light to be correctly guided along the fiber, reducing the amount of loss due to scattering, dispersion, and attenuation. The single-mode fiber is also designed to have an extremely low numerical aperture, which reduces the amount of light reflected off the surface of the fiber.
Single-mode fiber is a superior type of fiber for long-distance applications as it can reduce optical losses and transmission times significantly. It is also more future-proof as it is capable of handling next-generation high data rate services.