Optical fiber material and structure
What is fiber?
Optical fiber transmits signals in the form of light pulses, and uses glass or plexiglass as the network transmission medium. It consists of a fiber core, cladding and protective sheath.
Optical fibers can be divided into single-mode (Single Mode) optical fibers and multi-mode (Multiple Mode) optical fibers.
Single-mode fiber provides only one optical path and is complicated to process, but has larger communication capacity and longer transmission distance.
Multimode fiber uses multiple optical paths to transmit the same signal, and the transmission speed is controlled by the refraction of light.
There are the following categories of optical fibers used in computer networks
(1) 8.3pm core/125pm shell, single mode;
(2) 62.5um core/125um shell, multi-mode;
(3) 5OPm core/125pm shell, multi-mode;
(4)loopm core/140pm shell, multimode.
The main reason for the rapid development of optical cable is that it has the following characteristics:
(1) The transmission bandwidth is very wide and the communication capacity is large;
(2) Small transmission loss and long relay distance, especially suitable for long-distance transmission;
(3) Strong anti-lightning and anti-electromagnetic interference ability;
(4) The confidentiality is good, and it is not easy to be eavesdropped or intercepted;
(5) Small size and light weight;
(6) Low bit error rate and high transmission reliability;
(7) Prices are falling.
Optical fiber material and structure:
Optical fiber, short for optical fiber, is a fiber made of glass or plastic that acts as a light-transmitting tool. The main body of the core material is silicon dioxide, which is doped with a very small amount of other materials, such as germanium dioxide, phosphorus pentoxide, and the like. The effect of doping is to increase the optical refractive index of the material. The core diameter is about 5~75μm.
There is a cladding on the outside of the fiber, and the cladding has one layer, two layers (inner cladding, outer cladding) or multiple layers (called multi-layer structure), but the total diameter is around 100~200μm. The material of the cladding is generally pure silicon dioxide, and there is also a very small amount of boron trioxide. The effect of doping is to lower the optical index of refraction of the material.
In this way, the refractive index of the fiber core is slightly higher than that of the cladding. The difference between the two seats ensures that light is mainly confined to the fiber core for transmission. There is also a coating on the outside of the cladding, which can be silicon copper or acrylate. The role of the coating is to protect the optical fiber from external damage and increase the mechanical strength of the optical fiber. The outermost layer of the optical fiber is the jacket, which is a kind of plastic tube, which also plays a protective role. The plastic tubes of different colors can also be used to distinguish each optical fiber.
The principle of optical fiber:
Optical fiber actually refers to a core made of transparent material and a cladding made of a material with a slightly lower refractive index than the core around it. The medium in which the optical signal propagates in the fiber core. It is generally a symmetrical cylinder with a multilayer dielectric structure consisting of a core, cladding and coating layers.
Fiber has two main properties: loss and dispersion.
The loss or attenuation (dB/km) per unit length of the optical fiber is related to the length of the transmission distance of the optical fiber communication system and the selection of the distance between the repeater stations.
The dispersion response time delay distortion or pulse broadening of optical fiber is particularly important for digital signal transmission. The pulse width per unit length (ns/km) affects a certain transmission distance and information transmission capacity.