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Difference between single mode fibre and multimode fibre features? Which one is better to choose?

Difference between single mode fibre and multimode fibre features? Which one is better to choose?

zhubinyan |

The first is to introduce the difference between multi-mode optical fibre and single-mode optical fibre:

1, multi-mode optical fibre is the most primitive technology of optical fiber communication, this technology is the first time human beings achieve a revolutionary breakthrough in communication through optical fibers.

2, with the development of optical fibre communication technology, especially the development of laser technology and people's urgent need for long-distance, large information communication, people are looking for a better optical fibre communication technology ---- single-mode optical fibre communication.

3, fibre-optic communication technology has developed to the present day, many limitations inherent in multimode fibre-optic communication become more and more prominent:

① multimode light-emitting device for light-emitting diode (LED), light spectrum width, light wave impurity, light transmission dispersion, transmission distance is small. 1000M bit / s bandwidth transmission, reliable distance of 255 m (m). 100M bit / s bandwidth transmission, reliable distance of 2 km (km).

②Because of the inherent limitations of multimode light-emitting devices and the optical characteristics of multimode optical fibre, the bandwidth of multimode optical fiber communication is up to 1000M bit/s. 

4,single-mode optical fibre communication breaks through the limitations of multi-mode optical fibre communication:

①The bandwidth of single-mode optical fibre communication is large, usually more than 100G bit/s. In practice, it is generally divided into 155M bit/s and 155M bit/s. Practical use is generally divided into 155M bit/s, 1.25G bit/s, 2.5G bit/s, 10G bit/s.

② single-mode light-emitting device for the laser, the light spectrum is narrow, pure light waves, light transmission dispersion is small, the transmission distance. Single-mode lasers are divided into three types: FP, DFB and CWDM. FP lasers can usually transmit 60 kilometres (km), and DFB and CWDM lasers can usually transmit 100 kilometres (km).

5, digital optical transceiver using video uncompressed transmission technology to ensure that high-quality video signals in real time without delay transmission and to ensure that the image of high-definition and colour purity. This transmission method is a large amount of information data, more than 4-channel video of the optical transceiver are used more than 1.25G bit/s data stream transmission. 8-channel video data stream up to 1.5G bit/s.

Because the maximum bandwidth of multi-mode optical fibre is only 1G bit/s, if the multi-mode optical fibre transmission, it will inevitably result in information loss, a large number of video images appear snow or even white spots, data control malfunction.

Another fatal factor is the limitation of the transmission distance, multimode optical fibre 1G bit/s bandwidth transmission distance is theoretically 255 meters (m), if you take into account the optical link loss, the actual distance is also small tens of metres.

6, from the date of birth of single-mode optical fibre communication technology, it means the elimination of multi-mode optical fibre communication mode. At present, the multi-mode optical fibre transmission has been very little, just because of the inertia of the market and continue to this day, the optical fibre communication industry, this has long been an indisputable fact. We believe that we should be responsible for the user, responsible for the user's long-term needs of the spirit of reasonable proposals

According to the different modes of the transmission point, optical fibre can be divided into single-mode optical fibre and multi-mode optical fibre. The so-called "mode" refers to a beam of light entering the fibre at a certain angular velocity. Single-mode fibres use solid-state lasers as the light source, while multi-mode fibres use light-emitting diodes as the light source. Multimode fibres allow multiple beams of light to propagate through the fibre at the same time, resulting in mode dispersion (because each "mode" of light enters the fibre at a different angle and arrives at the other end at a different time, a feature known as mode dispersion). Mode dispersion limits the bandwidth and distance of multimode fibres, so multimode fibres have thick cores, low transmission speeds, short distances, and poor overall transmission performance, but they are relatively low-cost and are generally used in buildings or geographically contiguous environments. Single-mode optical fibre can only allow a beam of light to propagate, so single-mode optical fibre has no mode dispersion characteristics, thus, single-mode optical fibre has a correspondingly thin core, wide transmission bandwidth, high capacity and long transmission distance, but because it requires a laser source, the cost is higher.

Multimode Fibre

Optical signals in multimode fibre propagate through multiple pathways; usually recommended for applications at distances of less than a mile.

The effective distance from transmitter to receiver in multimode fibre is approximately 5 miles. The available range is also affected by the type and quality of the transmitting/receiving device; the stronger the light source and the more sensitive the receiver, the greater the range. Studies have shown that multimode fibre has a bandwidth of about 4000 Mb/s.

Single-mode fibres are manufactured to eliminate pulse broadening. Since the core size is very small (7-9 microns), light jumps are eliminated. Focused laser sources are used at 1310 and 1550 nm. These lasers are directed into the tiny fibre core and propagate to the receiver without significant jumps.

Single-mode fibre

Single-mode fibre has a thin core, allowing the light to be launched directly into the centre. It is recommended for longer distances.

Also, single mode signals have less distance loss than multimode. Over the first 3,000 feet, multimode fibre can lose up to 50% of its LED light signal strength, while singlemode loses only 6.25% of its laser signal over the same distance.

The bandwidth potential of single-mode makes it the only choice for high-speed and long-distance data transmission. Recent tests have shown that 64 channels of 40G Ethernet can be transmitted over a single single-mode fibre-optic cable over distances of up to 2,840 miles.

In security applications, the most common deciding factor for choosing multimode or singlemode is distance. If it's only child miles, multimode is preferred because the LED transmitter/receiver is much cheaper than the laser needed for singlemode. If the distance is greater than 5 miles, single mode fibre is best. Another issue to consider is bandwidth; if future applications are likely to include transmitting large bandwidth data signals, then single mode will be the best choice.

Single-mode fibre has only a single propagation path and is generally used for long-distance transmission, while multimode fibre has multiple propagation paths, the bandwidth of multimode fibre is 50MHz~500MHz/Km, and that of single-mode fibre is 2000MHz/Km, and the wavelengths of the fibre are 850nm, 1310nm, and 1550nm, etc. The 850nm wavelength region is for multimode fibre communication; 1550nm is for single-mode fibre communication; the wavelength region is for single-mode fibre communication; the wavelength region is for single-mode fibre communication. 850nm wavelength region for single-mode fibre communication; 1310nm wavelength region has two kinds of multimode and single-mode; 850nm attenuation is larger, but for 2~3MILE (1MILE=1604m) communication is more economical. Optical fiber size according to the fiber diameter is divided into 50μm slow-change multimode fiber, 62.5μm slow-change enhanced multimode fiber and 8.3μm mutant single-mode fiber, optical fiber cladding diameter are 125μm, so there are 62.5/125μm, 50/125μm, 9/125μm and so on the different kinds of different kinds of different kinds of different kinds of different kinds of different kinds of different kinds of different kinds of different kinds of different kinds of different kinds of different kinds of different kinds of different kinds of different kinds of different kinds of different kinds of different kinds of different kinds of different kinds of different kinds of optical fibers.

Fibre optic cable jacket identification, 50/125, 62.5/125 for multimode, 9/125 (g652) for single mode

Optical fibre can be ground to connect with 100/200 times magnification to see, a small black dot is single mode, a little larger with a double ring is multi-mode. Fibre core in the fusion splicer can also be distinguished, in the fusion splicer monitor to see the middle of the empty is single-mode, looks like one is multi-mode.

Simple difference in use: multi-mode is generally used in the park between the closer places;; single-mode is generally used in the park between the closer places; single-mode is generally used in the park between the closer places.

Single-mode transmission distance is farther, generally used in the field of telecommunications.

Single-mode transmission and multi-mode transmission

In the theory of optical fibre communication, optical fibre has single mode and multi-mode, the difference is:

1. single-mode fibre core diameter is small (about 10m m), allowing only one mode transmission, small dispersion, working at long wavelengths (1310nm and 1550nm), coupling with optical devices is relatively difficult

2. multi-mode fibre core diameter (62.5m m or 50m m), allowing hundreds of modes of transmission, large dispersion, working at 850nm or 1310nm, and the coupling of optical devices is relatively easy

As for the optical module, strictly speaking, there is no single-mode, multi-mode. The so-called single-mode, multi-mode module, refers to the optical module using optical devices and what kind of optical fibre with the best transmission characteristics.

Generally there are the following differences:

1. single-mode modules generally use LDs or LEDs with narrower spectral lines as the light source, the coupling component size and the single-mode optical fibre with a good match, the use of single-mode optical fibre transmission can be transmitted over a longer distance

2. multi-mode modules generally use lower-priced LED as the light source, coupling component size and multi-mode optical fibre with a good fit

1、Classification of optical fibre

Optical fibre can be divided into single-mode and multi-mode according to the transmission mode of light in it. Multimode optical fibre core diameter of 50 or 62.5μm, cladding outer diameter of 125μm, said 50/125μm or 62.5/125μm. single-mode optical fibre core diameter of 8.3μm, cladding outer diameter of 125μm, said 8.3/125μm.

Fibre optic operating wavelengths are short-wave 850nm, long-wave 1310nm and 1550nm. fibre optic loss generally decreases with the increase in wavelength, 850nm loss is generally 2.5dB/km, 1.31μm loss is generally 0.35dB/km, 1.55μm loss is generally 0.20dB/km, this is the lowest loss in optical fibres, the wavelength of 1.65μm. The loss above 1.65μm tends to increase. Due to OHˉ (water peak) absorption, 900 ~ 1300nm and 1340nm ~ 1520nm range of loss peaks, these two ranges are not fully utilised.

2、Multi-mode optical fibre

Multi Mode Fibre (Multi Mode Fiber) - core thicker (50 or 62.5μm), can transmit a variety of modes of light. However, its intermodal dispersion is large, which limits the frequency of transmission of digital signals, and with the increase in distance will be more serious. As a result, multimode optical fibre transmits over relatively short distances, typically only a few kilometres. The table below shows a comparison of the bandwidth of multimode fibre optic cables:

When it comes to 10 Gigabit multimode optical cable, some clarification is needed. Optical fibre system cannot be separated from optical transceiver and optical fibre when transmitting optical signals. Because the traditional multi-mode optical fibre can only support 10 Gigabit transmission of several tens of meters, in order to match the 10 Gigabit application of the new optical transceiver, ISO/IEC 11801 developed a new multi-mode optical fibre standard class, that is, the OM3 category, and in September 2002 was officially promulgated. OM3 optical fibre on the LED and laser bandwidth of the two modes are optimized, and at the same time need to be certified by the rigorous DMD test. Fiber optic cabling system using the new standard can support at least 10 Gigabit transmission to 300 meters in the multi-mode mode, while in the single-mode mode can reach more than 10 kilometres (1550nm can support 40 kilometres of transmission).

3, single-mode fibre optic cable

Single mode optical fibre (Single Mode Fiber): the central core is very thin (core diameter is generally 9 or 10μm), can only transmit a mode of light. Therefore, its intermode dispersion is very small, suitable for long-distance communication, but there are also material dispersion and waveguide dispersion, so that the single mode optical fibre on the spectral width of the light source and the stability of the high requirements, that is, the spectral width should be narrow, and the stability of the light source should be good.

Later, it was found that the total dispersion of single-mode fibre was zero at 1310 nm. From the point of view of the loss characteristics of optical fibres, 1310nm is exactly a low-loss window of optical fibres. In this way, the 1310nm wavelength region has become an ideal working window for optical fiber communication, and is now the main working band of practical optical fiber communication system.The main parameters of the 1310nm conventional single-mode optical fiber are determined by the International Telecommunication Union ITU-T in the G652 recommendations, so this optical fiber is also known as the G652 optical fiber.

4, Conclusion: single mode or multi-mode good?

Comprehensive analysis of the above, we believe that the user should be from the application point of view, the transmission distance point of view, forward-looking point of view, cost point of view, a combination of the above factors, to the lowest price to invest in the best performance!