Single-mode fiber can only transmit single-mode signals, while multimode fiber can transmit multi-mode signals.
Multimode optical fiber (Multimode optical fiber = MMF):
As the name implies, it is an optical fiber capable of propagating multiple modes of electromagnetic waves (here, of course, light waves);
Therefore, there is a large intermodal dispersion, and the information capacity that can be transmitted is small; the core of the multimode fiber is relatively large, generally
50um, the numerical aperture is about 0.2; the number of modes depends on the diameter, numerical aperture and wavelength of the fiber core
Single-mode fiber (Single-mode fiber = SMF):
It can only transmit signal waves of one mode, but it must meet the conditions: I seem to remember that it is related to the thing called normalized frequency in the textbook, and the fiber core needs to be thinner, preferably 3 or 4 of the working wavelength. times; so single-mode light is much thinner than multimode fiber in terms of appearance; single-mode fiber does not have modal dispersion because it only transmits one mode.
Multimode fiber is used for small-capacity, short-distance systems, and single-mode fiber is used for backbone, large-capacity, and long-distance systems. The core diameter of single-mode fiber is generally 9/125 and multimode is 50/125 or 62.5/125.
Single-mode and multi-mode are relative to specific wavelengths, and the same fiber may be single-mode or multi-mode at different wavelengths.
Light is not divided into single and multi-mode, and light sources can be divided into single-mode (dfb) and multi-mode (fp) .
The fiber diameter of multimode fiber is thinner than that of single mode, the single mode 652 is 62.5/125, and the multimode has 50/125 and 62.5/125. In terms of price, multi-mode is generally 1.5-2 times that of single-mode with the same core number. From the perspective of practical application, multimode is basically used in data access optical cables. The biggest disadvantage of multimode compared with single mode is inter-mode dispersion (due to the same
different speeds of light in different modes).
In the past, 62.5/125 multimode fiber was mainly used. As for the difference between the two, it seems that the purpose of cable is different. 50 is mostly used for indoor optical cables.
Single-mode fiber only transmits one mode of the fundamental mode, and multimode can transmit multiple modes. Single-mode is mainly used for long-distance trunk lines, and multi-mode is used for local areas. Some people said that the single-mode is much thinner than the multi-mode, which is actually wrong. The diameters of the two fiber claddings are both 125, but the diameter of the ferrule is different. . In general, single-mode is not directly connected to multi-mode, but through equipment conversion.
Optical fibers are divided into two types: multimode optical fibers and single-mode optical fibers. The difference between multimode optical fibers and single-mode optical fibers is mainly in the different transmission methods of light, and of course the bandwidth capacity is also different. The diameter of the multimode fiber is large, and the light beams of different wavelengths and phases are continuously reflected along the fiber wall and transmitted forward, causing dispersion, which limits the transmission distance and bandwidth between the two repeaters.
The bandwidth is about 2.5Gbps. The diameter of the single-mode fiber is thinner, and the light propagates in a straight line without reflection, so the dispersion is reduced, the bandwidth is increased, and the transmission distance is also lengthened. However, the price of the matching optical end equipment is relatively high, and the bandwidth of the single-mode optical fiber exceeds 10Gbps.
Multimode fiber is greatly affected by the expansion (dispersion) of pulse signals with higher modes, while single-mode fiber better solves the problem of intermodal dispersion. SMF CORE 8.3-9.3 um. MFD is usually 9.3um