Many weak friends have repeatedly quoted us about the choice of fiber single-mode and multi-mode. Fiber is widely used in integrated wiring. Most people will encounter fiber single-mode and multi-mode selection. Let's get to know everyone today. Knowledge of this aspect.

1、Fiber classification

The transmission mode of the optical fiber in the light can be divided into single mode and multi mode. The multimode fiber has a core diameter of 50 or 62.5 μm and a cladding outer diameter of 125 μm, expressed as 50/125 μm or 62.5/125 μm. The single mode fiber has a core diameter of 8.3 μm and a cladding outer diameter of 125 μm, which is expressed as 8.3/125 μm.

The operating wavelength of the fiber is short wavelength 850 nm, long wave 1310 nm and 1550 nm. The fiber loss generally decreases with increasing wavelength. The loss at 850 nm is generally 2.5 dB/km, the loss at 1.31 μm is generally 0.35 dB/km, and the loss at 1.55 μm is generally 0.20 dB/km, which is the lowest loss of the fiber. The loss of the wavelength of 1.65 μm or more tends to increase. Due to the absorption of OHˉ (water peak), there are loss peaks in the range of 900~1300nm and 1340nm~1520nm, and these two ranges are not fully utilized.

2、Multimode fiber optic cable

Multi Mode Fiber - The core is thick (50 or 62.5μm) and can transmit multiple modes of light. However, the dispersion between the modes is large, which limits the frequency of transmitting digital signals, and is more serious as the distance increases. Therefore, the distance traveled by multimode fiber is relatively close, usually only a few kilometers. The following table shows the comparison of the bandwidth of multimode fiber optic cable:

When it comes to 10G multimode fiber optic cable, it needs to be explained. The optical fiber system cannot be separated from the optical transceiver and optical fiber when transmitting optical signals. Because traditional multimode fiber can only support 10 Gigabit transmission for several tens of meters, ISO/IEC 11801 has developed a new multimode fiber standard class, OM3 category, in 2002. Officially promulgated in September. OM3 fiber is optimized for both LED and laser bandwidth modes and is subject to rigorous DMD testing. The new standard fiber-optic cabling system can support at least 10 Gigabit transmission to 300 m in multimode mode, and can reach more than 10 km in single mode mode (1550 nm can support 40 km transmission).

CommScope's multimode fiber optic cable is divided into:

(1), multimode OptiSPEEDreg;

(2), solution (62.5/125μm) and 10G multimode LazrSPEEDreg;

(3), solution (laser optimized 10G 50/125μm).

LazrSPEED is divided into three series, namely LazrSPEED 150, 300, 550 series, and LazrSPEED 10G multimode fiber optic cable is UL DMD certified. Please refer to the following table for specific transmission indicators:

　　From the above table, the comparison standard shows that CommScope's fiber optic cable far exceeds the standard defined in the standard.

Therefore, if you want to choose multimode fiber optic cable, you should consider the following points:

A. From the future development trend, the horizontal cabling network rate needs 1 Gb/s bandwidth to the desktop, the building backbone network needs to be upgraded to 10 Gb/s rate bandwidth, and the campus backbone network needs to be upgraded to 10 Gb/s or 100 Gb/s. Rate bandwidth. At present, network applications are growing at a rate of about 50% per year. It is expected that Gigabit to the desktop in the next five years will become as common as the current one hundred megabytes to the desktop. Therefore, it is necessary to be forward-looking in current system planning. For Category 6 cabling, the backbone part should consider 10 Gigabit multimode fiber optic cable, especially the current cost of Category 6 copper plus Gigabit multimode fiber optic cable and Super Category 5 copper plus Gigabit multimode fiber optic cable is less than 10~20%. The difference between the left and right, from the perspective of long-term application, such as the cost of allowing the use of Category 6 copper plus 10 Gigabit fiber optic cable.

B. From the investment point of view, OptiSPEED (ordinary multimode 62.5/125) is used in places where 10G will not be used for at least 10 years; because OM3 fiber optic cable uses low-cost VCSEL and 850nm light source equipment, the cost of 10G transmission is greatly reduced. . If the distance does not exceed 150 meters, choose LazrSPEED 150 (OM2 50/125 supports 10G 150m); LazrSPEED 300 is the best choice for 300m 10G transmission; LazrSPEED 550 is the best choice for 550m 10G transmission; For 550-meter 10G transmission requirements, you need to choose TeraSPEED, a single-mode fiber-optic cable system.

3、Single mode optical cable

Single Mode Fiber: The center core is very thin (the core diameter is generally 9 or 10 μm), and only one mode of light can be transmitted. Therefore, the inter-mode dispersion is small, suitable for remote communication, but there are also material dispersion and waveguide dispersion, so that single-mode fiber has high requirements on the spectral width and stability of the light source, that is, the spectral width is narrow and stable. It’s better.

It was later found that at a wavelength of 1310 nm, the total dispersion of the single mode fiber is zero. From the loss characteristics of the fiber, 1310nm is just a low loss window of the fiber. Thus, the 1310 nm wavelength region has become an ideal working window for fiber-optic communication, and is also the main working band of practical fiber-optic communication systems. The main parameters of the 1310nm conventional single-mode fiber are determined by the International Telecommunication Union ITU-T in the G652 recommendation, so this fiber is also called G652 fiber.

It is mentioned above that due to the absorption of OHˉ (water peak), there is a loss peak in the range of 900 to 1300 nm and 1340 nm to 1520 nm, which is called a water peak. At present, the TeraSPEEDTM zero-water peak single-mode optical cable provided by CommScope of the United States is solving this problem. The TeraSPEED system provides users with a wider transmission bandwidth by eliminating the influence factor of the 1400nm water peak, and users can freely use from 1260nm. By all the bands of 1620nm, the transmission channel has been increased from the previous 240 to 400, and the performance is 50% more than the traditional single-mode fiber, which lays a solid foundation for the CWDM coarse wavelength division multiplexing technology that will be upgraded to 100G bandwidth in the future. The TeraSPEED solution is the ideal backbone fiber system for the campus/city level.

At the same time, since G.652.D is the latest indicator of single-mode fiber, it is the most stringent and fully backward compatible of all G.652 levels. If you only indicate that G.652 means the performance specification of G.652.A, you should pay special attention to this. TeraSPEED fiber exceeds all specifications to meet the performance specifications of G.652.A, .B, .C and .D, as shown in the following table:

And our recommendations for the selection of single-mode fiber cables are as follows:

A. From the perspective of transmission distance, if you want to support 10 Gigabit transmission in the future, you should consider using single-mode fiber optic cable for a long distance.

B. From the perspective of cost, the zero-water peak cable provides 50% more bandwidth than single-mode fiber, and the cost is similar. In fact, CommScope does not currently provide ordinary single-mode fiber, and only provides zero-water peak fiber. High performance products to users.　　

4、Conclusion: Single mode or multimode?

　Based on the above analysis, we believe that users should combine the above factors from the perspective of application, transmission distance, forward-looking perspective, and cost, and invest in the best performance at the lowest price!

Single-mode is generally two-core, one core receives one core hair; also single-fiber two-way uses one core, and realizes bidirectional transmission (single-mode fiber-optic wavelength division multiplexer WDM) through WDM technology on the same core.

Multimode is two-core, there is no single core, because multimode fiber cable can't do WDM.

Single-fiber two-way transceivers are more expensive, and the price of a pair is comparable to the price of two pairs of two-fiber two-way.

Price: Multi-mode cheap, single-mode expensive

Distance: multimode is less than 2KM, single mode can pass around 100KM

Wavelength: multimode 850/1310NM, single mode 1310/1550NM

The multimode transceiver receives multiple transmission modes with a relatively short transmission distance.

Single mode transceivers only accept a single mode. The transmission distance is relatively long.

As for the large amount of consumption, it is difficult to say that although multi-mode is in the process of elimination, but because of the lower price, there are still many uses in monitoring and close-range transmission.

Use the reference table:

Note: What is the difference between a multimode fiber transceiver and a single mode fiber transceiver?

The multimode transceiver corresponds to the multimode fiber, and the single mode and the single mode correspond to each other and cannot be mixed.

At present, multi-mode transceivers are cheap, basically 200 yuan is very good, more than 300 enterprise-level is enough. The bandwidth is 100Mbps.

Compared with single-mode transceivers, there are fewer sources on the market, and the price is more expensive. The bandwidth is 1000 Mbps, which is much higher than multi-mode.

For specific applications, the multi-mode usage is higher than that of single-mode, mainly in the wiring range below 500m, and multi-mode can already be satisfied, although the performance is not as good as single-mode. Applications with single mode above 500m or high bandwidth requirements are mostly enterprise applications.

Because the working stability and performance of the fiber optic module is much better than that of the transceiver, in the single-mode application environment with high performance requirements, few companies will use the transceiver, but instead use the module instead, natural production. There are fewer manufacturers of single-mode transceivers, and the price is higher.

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