Multi mode fiber - with a thick core (50 or 62.5 μ m), it can transmit multiple modes of light. However, the intermodal dispersion is large, which limits the frequency of digital signal transmission, and it will be more serious with the increase of distance. Therefore, the distance of multimode optical fiber transmission is relatively short, generally only a few kilometers.
Distinction of optical cable
Single mode fiber can only transmit single-mode signal, while multimode fiber can transmit multimode signal
As the name suggests, it is an optical fiber that can propagate multiple modes of electromagnetic waves (optical waves, of course). Because there are multiple modes of transmission, there is a large inter mode dispersion, which can transmit small information capacity. The core of multimode optical fiber is large, generally 50um, and the numerical aperture is about 0.2. The number of modes depends on the diameter, numerical aperture and wavelength of the core.
Single mode fiber
Only one mode of signal wave can be transmitted, but it must meet the conditions: it seems that the textbook says that it is related to the thing called normalized frequency, and the fiber core needs to be thinner, preferably 3 or 4 times of the working wavelength; therefore, the single-mode fiber is much thinner than the multi-mode fiber in appearance; because the single-mode fiber only transmits one mode, there is no mode dispersion
Multimode fiber is used in small capacity and short distance system. Single mode fiber is used in trunk, large capacity and long distance systems.
The core diameter of single-mode fiber is generally 9 / 125, while that of multimode fiber is 50 / 125 or 62.5/125.
Single mode and multimode are relative to specific wavelengths. The same fiber may be single mode or multimode at different wavelengths.
Light source can be divided into single longitudinal mode (DFB) and multi longitudinal mode (FP).
The diameter of multimode fiber is smaller than that of single-mode fiber. Single mode 652 is 62.5/125, while multimode fiber has 50 / 125 and 62.5/125. In terms of price, multimode fiber is generally 1.5 ~ 2 times of single-mode fiber with the same number of cores. In practical application, multimode fiber is basically used in data access cable. The biggest disadvantage of multimode fiber is intermodal dispersion (due to the speed of the same light in different modes) Different).
Optical fiber is divided into multimode fiber and single-mode fiber. The difference between multimode fiber and single-mode fiber mainly lies in the different transmission modes and bandwidth capacity.
The diameter of multimode fiber is large, and the beams of different wavelengths and phases are continuously reflected along the fiber wall, resulting in dispersion, which limits the transmission distance and bandwidth between the two repeaters. The bandwidth of multimode fiber is about 2.5Gbps.
The diameter of the single-mode fiber is small, and the light propagates in a straight line and seldom reflects, so the dispersion is reduced, the bandwidth is increased and the transmission distance is lengthened. However, the price of the supporting optical terminal equipment is high, and the bandwidth of single-mode fiber is more than 10Gbps.
Multimode optical cable is a communication cable with multiple optical fibers (silicon dioxide, quartz glass) built in. It has a variety of structure models and two kinds of transmission modes. It is a widely used communication optical cable, which is mainly used in the transmission of long-distance communication and inter office communication.
Multi mode optical cable transmission: in terms of transmission, 8-core multi-mode optical cable mainly adopts single-mode and multi-mode specifications. Single mode (inner diameter is 9 μ m, outer diameter is 125 μ m) multimode (there are two kinds: inner diameter is 62.5 μ m, outer diameter is 125 μ m, inner diameter is 50 μ m, outer diameter is 125 μ m), single mode is a long-distance transmission mode, with wavelengths of 1310 and 1550; multimode is a short-distance transmission mode (transmission distance is limited to 2000 meters), with wavelengths of 850 and 1300. (single mode is widely used, while multi-mode is being phased out)
多模光纤(Multi Mode Fiber) - 芯较粗(50或62.5μm)，可传多种模式的光。但其模间色散较大，这就限制了传输数字信号的频率，而且随距离的增加会更加严重。因此，多模光纤传输的距离就比较近，一般只有几公里。