The relationship between optical fiber transmission loss and wavelength is an important issue in the field of optical fiber communication, because different wavelengths of light will encounter different loss mechanisms when propagating in optical fibers. The losses in optical fibers mainly include absorption losses, scattering losses, and bending losses, and these loss mechanisms are closely related to the wavelength of light waves. This article will analyze in detail the relationship between these two.
1, Absorption loss
Absorption loss refers to the energy loss caused by the absorption effect of the fiber material itself when light waves propagate in the fiber material. Fiber optic materials, mainly silicon dioxide (SiO2), absorb more light energy at certain wavelengths, such as the OH - ion absorption peak in the infrared region and the electron transition absorption in the ultraviolet region. The typical low loss window is located around 850nm, 1310nm, and 1550nm, as the absorption of fiber materials is minimal at these three wavelengths.
2, Scattering loss
Scattering losses mainly include Rayleigh scattering and nonlinear scattering. Rayleigh scattering is caused by microscopic inhomogeneity in optical fiber materials, which can cause a portion of the energy of light waves to deviate from their original propagation direction. The Rayleigh scattering loss is inversely proportional to the fourth power of the wavelength, which means that the longer the wavelength, the smaller the scattering loss. At a wavelength of 1550nm, Rayleigh scattering loss is minimized.
Nonlinear scattering, such as Raman scattering and Brillouin scattering, is related to wavelength and light intensity, but overall it can be well controlled in the long wavelength region.
3, Bending loss
Bending loss occurs during fiber bending, especially when the bending radius is small. When light waves propagate in bent optical fibers, some of the light rays will escape the fiber cladding due to refraction, resulting in energy loss. The relationship between bending loss and wavelength is complex, but generally speaking, when the wavelength is longer, the bending loss is relatively small because long wavelength light is more likely to remain confined in the fiber.
In summary, optical fibers have relatively low losses in the three wavelength windows of 850nm, 1310nm, and 1550nm. Among them, the loss in the 1550nm window is the smallest, ranging from 0.19dB/km to 0.25dB/km, making 1550nm the preferred wavelength for long-distance optical fiber communication. In addition, due to the small dispersion of optical fibers at 1550nm wavelength, they also have advantages in high-speed transmission.
Choosing the appropriate wavelength is crucial for optimizing the performance of fiber optic communication systems. Considering factors such as loss, dispersion, nonlinear effects, and cost, a choice is usually made between the three wavelengths of 850nm, 1310nm, and 1550nm to meet different application requirements. For example, short-range local area networks may use 850nm, while long-distance backbone networks tend to use 1550nm.
