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Fiber cut-off wavelength

2021-10-25
The fiber cut-off wavelength is to ensure that only one mode exists in the fiber.
One of the main transmission characteristics of single-mode fiber is the cut-off wavelength, which is of great significance for fiber optic cable manufacturers and users of fiber optic cables to design and use fiber optic transmission systems.

The normal transmission mode of single-mode fiber is linear polarization mode, (including two orthogonal modes). The so-called cut-off wavelength refers to the cut-off wavelength of higher-order modes (including four degenerate modes composed of two circular polarization modes and two orthogonal modes). The operating wavelength of the single-mode optical fiber transmission system must be greater than the cut-off wavelength, otherwise, the optical fiber will work in the dual-mode area. Due to the existence of modes, mode noise and multi-mode dispersion will be generated, which will lead to the deterioration of transmission performance and the reduction of bandwidth. Figure 1 shows the eigenfunctions and curves of a single fiber, as well as the refractive index profile distribution. It can be seen from Figure 1 that the working area of a single-mode fiber is:

Normalized frequency


In the formula, a is the core radius, is the core and cladding refractive index, and λ is the working wavelength. V=2.4048 is the cut-off value of the modulus. When the structural parameters of the optical fiber are timed, the cut-off wavelength of the optical fiber is:


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