Fiber Cable Manufacturer
1-288 cores GYFTY non-metallic Optical Fiber Cable
Central strength member
Vary from 7 to 14mm
aerial or duct cable networking system
1/2/3/4/5km km each exporting wooden drums
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What is "Modal Distribution" ?
In multimode fibers, some light rays travel straight down the axis of the fiber while all the others wiggle or bounce back and forth inside the core. In step index fiber, the off axis rays, called "higher order modes" bounce back and forth from core/cladding boundaries as they are transmitted down the fiber. Since these high order modes travel a longer distance than the axial ray, they are responsible for the dispersion that limits the fiber's bandwidth.
In graded index fiber, the reduction of the index of refraction of the core as one approaches the cladding causes the higher order modes to follow a curved path that is longer than the axial ray (the "zero order mode"), but by virtue of the lower index of refraction away from the axis, light speeds up as it approaches the cladding and it takes approximately the same time to travel through the fiber. Thus the "dispersion" or variations in transit time for various modes, is minimized and bandwidth of the fiber is maximized.
However, the fact that the higher order modes travel farther in the glass core means that they have a greater likelihood of being scattered or absorbed, the two primary causes of attenuation in optical fibers. Therefore, the higher order modes will have greater attenuation than lower order modes, and a long length of fiber that was fully filled (all modes had the same power level launched into them) will have a lower amount of power in the higher order modes than will a short length of the same fiber.
This change in "modal distribution" between long and short fibers can be described as a "transient loss", and can make big differences in the measurements one makes with the fiber. It not only changes the modal distribution, it changes the effective core diameter and numerical aperture also.
The term "equilibrium modal distribution" (EMD) is used to describe the modal distribution in a long fiber which has lost the higher order modes. A "long" fiber is one in EMD, while a "short" fiber has all its initially launched higher order modes.