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The difference between single mode fiber and multimode fiber explains the advantages and disadvantages of both
Nov 07, 2018

According to the transmission mode of light in the optical fiber, it can be divided into: single mode and multimode fiber, single mode and multimode, only one word difference, then what is the difference between the two, just the difference in the number of simple touches? To understand the difference between the two.


Single-mode fiber can only transmit single-mode signals, while multi-mode fiber can transmit multi-mode signals. Multi-mode fiber: as the name suggests, is an optical fiber capable of propagating multiple modes of electromagnetic waves (here, of course, light waves); Therefore, there is a large inter-mode dispersion, and the information capacity that can be transmitted is small; the multimode fiber core is large, generally 50 micrometers, and the numerical aperture is about 0.2; the number of modes depends on the diameter of the core, the numerical aperture and wavelength.


Single-mode fiber: only one mode of signal wave can be transmitted, but it must be qualified: it seems to remember that the material is related to the thing called normalized frequency. The core needs to be finer, preferably the working wavelength. 3,4 times; so single-mode light is much thinner than multimode fiber; single-mode fiber has no modal dispersion because it only transmits one mode.


Multimode fiber is used for small-capacity, short-distance systems, single-mode fiber for trunk, large-capacity, long-distance systems. Single-mode fiber core diameter is typically 9/125, while multimode is 50/125 or 62.5 / 125.


Single mode and multimode are relative to a specific wavelength. The same fiber may be single mode or multimode at different wavelengths. Light is not divided into single modes. The light source has single longitudinal mode (DFB) and multiple vertical. In the mode (FP), multimode fiber is finer than single mode in fiber diameter, single mode 652 is 62.5 / 125, and multimode is 50/125 and 62.5 / 125. In terms of price, multimode Generally speaking, it is 1.5 to 2 times of the same-core single mode. From the practical point of view, multi-mode is basically used in data access optical cable. The biggest disadvantage of multi-mode relative to single-mode is inter-mode dispersion (due to The same kind of light has different rates in different modes).


The main use in the country is 62.5 / 125 multimode fiber, as the difference between the two seems to be different after the use of cable, 50 for the indoor cable.


Single-mode fiber only transmits a mode of the fundamental mode, and multi-mode can transmit multiple modes. Single mode is mainly used for long-distance trunks, and multi-mode is used for local areas. Some people say that single mode is much thinner than multimode. Actually, it is wrong. The diameter of both fiber claddings is 125, but the core diameter is different. The single mode is 9 and the common mode is 50 and 62.5. In general, single mode does not directly interface with multimode is through device conversion.


Optical fiber is divided into two types: multimode fiber and single mode fiber. The difference between multimode fiber and single mode fiber is mainly due to the different optical transmission modes. Of course, the bandwidth capacity is also different. The multimode fiber has a large diameter, and the beams of different wavelengths and phases are reflected and transmitted forward along the fiber wall, causing dispersion, which limits the transmission distance and bandwidth between the two repeaters. The bandwidth of the multimode fiber is about 2.5Gbps. The single-mode fiber has a relatively small diameter, and the light propagates in a straight line therein, and is rarely reflected, so the dispersion is reduced, the bandwidth is increased, and the transmission distance is also lengthened. However, the optical equipment that is matched with it is expensive, and the bandwidth of single-mode fiber exceeds 10 Gbps.


Multimode fiber is affected by the higher pulse signal spread (dispersion) of the mode, and the single mode fiber better solves the problem of dispersion between modes. SMF core 8.3-9.3. The MFD is usually 9.3um.


In security applications, the most common determinant of choosing multimode or singlemode is distance. If there are only a few miles, the multimode is preferred because the LED transmitter/receiver is much cheaper than the laser required for a single mode. If the distance is greater than 5 miles, the best consideration for single-mode fiber is bandwidth; if future applications may include transmitting large bandwidth data signals, single mode will be the best choice.


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