Introduction to some knowledge of Optical fiber cable

Optical fiber cable transmission is based on the principle of total reflection of available light at the interface of two media. For abrupt optical fiber cable, n1 is the refractive index of the core medium, n2 is the refractive index of the cladding medium, n1 is greater than n2, and the light entering the core reaches the interface between the core and the cladding (referred to as the core-cladding interface). When the incident angle is greater than the critical angle of total reflection θc, total reflection can occur without light energy passing through the core, and the incident light can be transmitted forward at the interface through numerous total reflections.

It turns out that when the optical fiber cable is bent, the normal of the interface is turned and the incident angle is small, so the incident angle of a part of the light becomes smaller than θc and cannot be totally reflected. However, those rays with a larger incident angle can still be totally reflected, so the optical fiber cable can still transmit light when it is bent, but it will cause energy loss. Generally, when the bending radius is greater than 50-100 mm, the loss can be ignored. Small bends will cause severe "microbend losses".

People often use electromagnetic wave theory to further study the mechanism of optical fiber cable transmission, and solve the wave equation by the boundary conditions of the optical fiber cable dielectric waveguide. Light propagating in an optical fiber cable contains many modes, each of which represents an electromagnetic field distribution and corresponds to a certain ray described in geometrical optics. The conduction modes present in the Optical fiber cable depend on the normalized frequency ν value of the Optical fiber cable.

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