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About Fiber Bending

A friend asked, will there be loss in fiber bending? How much does it bend without loss?


The problem of fiber bending often occurs in actual projects. In the project, the fiber is bent. Many friends have no idea whether this will affect the transmission of the fiber. So this issue will let you learn about this aspect together.


Have you ever experienced the sudden disconnection of WIFI, have you experienced repeated restarts, and still feel that the network speed is slow? In addition to the router itself, the reason for these problems may be a problem with the fiber optic cable.

When the fiber is excessively bent, the power loss increases significantly.


When light enters from one end of the fiber and exits from the other end, the intensity of the light decreases, which means that after the optical signal propagates through the fiber, the light energy is attenuated. This shows that there are certain substances in the optical fiber or for some reason, blocking the passage of optical signals. This is the transmission loss of the fiber. Only by reducing the fiber loss can the optical signal be unimpeded.


The main factors that cause fiber loss are: intrinsic, bending, extrusion, impurities, unevenness and butt joint, etc. Among them, the fiber bending loss is mainly caused by man-made.


Optical fibers are very sensitive to bends, excessive bending = light spillage. If the bend is too large, most of the light will spill out of the coating. Singlemode is more sensitive to bend loss than multimode.




Optical loss occurs in two types of fiber bending:

Macrobend (Macrobend) and Microbend (Microbend).


Macrobend refers to a bend whose curvature radius is much larger than the diameter of the fiber. The fiber bend in the demonstration video is a macrobend.




When the macrobending is corrected, it can be restored.




Microbending refers to micron-scale bending of the fiber axis, for example, caused by excessively tight bundling.




The propagation of light in optical fiber is mainly based on the principle of total reflection. When the light is incident perpendicular to the end face of the light and coincides with the axis of the fiber, the light propagates forward along the axis. If the curvature is too large, part of the light cannot pass through normally, which will lead to a decrease in optical power, resulting in poor quality of received light. The speed is slow.


A certain degree of large-angle bending increases the loss of the optical fiber and reduces the signal-to-noise ratio. If the signal-to-noise ratio is small, the bandwidth may be small (actually, the number of broken packets increases and the number of retransmissions increases).

Under normal circumstances, when the optical fiber is long, it can be coiled into a ring and then bound together. However, it should be noted that the diameter of the circle should not be too small to avoid excessive curvature and the optical signal cannot be refracted to the opposite end. Generally, the diameter should not be smaller than 10 cm (that is, the radius is 5 cm) is appropriate, remember not to fold in half.


Optical fiber is soft and can be bent, but after bending to a certain extent, although the optical fiber can guide light, it will change the transmission path of light. The transmission mode is converted to the radiation mode, so that a part of the light energy penetrates into the cladding or passes through the cladding to become a radiation mode and leaks outward, resulting in loss. When the bending radius is larger than 5-10cm, the loss caused by bending can be neglected.


G.657 fiber is the latest type of fiber developed on the basis of G.652 fiber in order to achieve the goal of fiber-to-the-home. The most important feature of this type of optical fiber is its excellent bending resistance, and its bending radius can be 1/4 to 1/2 of that of conventional G.652 optical fibers.


G.657 fiber is divided into two subcategories, A and B. The performance and application environment of G.657A fiber are similar to those of G.652D fiber. C, L5 working bands) work.


G.657B optical fiber mainly works in three wavelength windows of 1310nm, 1550nm and 1625nm, which is more suitable for realizing FTTH information transmission and installing in narrow places such as indoors or buildings.