fiber transmission rate
So what is the basic principle of optical fiber transmission, we have done the following analysis:
Optical fiber transmission is based on the principle of total reflection of available light at the interface of two media. For abrupt fiber, 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 incident angle when the light entering the core reaches the interface between the core and the cladding (referred to as the core-cladding interface) When it is greater than the critical angle of total reflection θc, total reflection can occur and no light energy can penetrate the fiber core, and the incident light can be transmitted forward through countless times of total reflection at the interface.
It turns out that when the fiber is bent, the interface normal turns and the incident angle is small, so the incident angle of some light rays becomes smaller than θc and cannot be totally reflected. However, those rays with larger incident angles can still be totally reflected, so the light can still be transmitted when the fiber is bent, but it will cause energy loss. Generally, when the bending radius is greater than 50-100 mm, the loss is negligible. Small bends will cause severe "microbend loss".
The electromagnetic wave theory is often used to further study the mechanism of optical fiber transmission, and the wave equation is solved by the boundary conditions of the optical fiber dielectric waveguide. The light propagating in the optical fiber contains many modes, each mode represents an electromagnetic field distribution, and corresponds to a certain ray described in geometric optics. The conduction modes present in a fiber depend on the normalized frequency ν value of the fiber.
Where NA is the numerical aperture, which is related to the refractive index of the core and cladding medium. ɑ is the radius of the fiber core, and λ is the wavelength of the transmitted light. When the fiber is bent, mode coupling occurs, and a part of the energy is transferred from the conduction mode to the radiation mode, and is lost outside the core.
