What is single mode fiber?
Single mode fiber: the central glass core is very thin (the core diameter is generally 9 or 10m), which can only transmit one mode of fiber. Therefore, the intermodal dispersion is very small, which is suitable for remote communication.
What is multimode fiber?
Multimode optical fiber jumper adopts multimode optical fiber, with connectors at both ends to realize the connection from equipment to optical fiber wiring link. It has a thick protective layer, and is generally used for the connection between optical terminal and terminal box. Multimode fiber allows different modes of light to be transmitted on one fiber. Due to the large core diameter of multimode fiber, relatively cheap couplers and connectors can be used. The core diameter of multimode fiber is 50m to 100m.
What is the difference between single mode fiber and multimode fiber?
Single mode fiber only has a single propagation path, which is generally used for long-distance transmission. The bandwidth of single-mode fiber is 2000MHz / km, 1550nm wavelength region is single-mode fiber communication mode; 1310nm wavelength region has two kinds of multimode and single-mode. The core diameter of single-mode fiber is small (about 10 mm), only one mode transmission is allowed, and the dispersion is small. It works at long wavelengths (1310 nm and 1550 nm), so it is difficult to couple with optical devices. Single mode optical fiber is mostly used in the lines with long transmission distance and relatively high transmission rate, such as long-distance trunk line transmission, man construction, etc. Generally, the optical fiber jumper is yellow, the connector and protective sleeve are blue, and the transmission distance is long.
Multimode fiber The 850nm wavelength region is the multimode optical fiber communication mode; the multimode optical fiber is mostly used in the network with relatively low transmission rate and relatively short transmission distance, such as local area network, etc. in this kind of network, there are usually many nodes, many joints, many bends, large amount of connectors and couplers, and many light sources per unit fiber length. The use of multimode optical fiber can effectively reduce the cost of network Network cost. The core diameter of multimode fiber is large (62.5mm or 50mm), allowing hundreds of modes to transmit, with large dispersion, working at 850nm or 1310nm. Coupling with optical devices is relatively easy. Generally, optical fiber jumpers are represented by orange, some are represented by gray, and connectors and protective sleeves are represented by beige or black; the transmission distance is short. Multimode fiber jumper also has 10 Gigabit multimode fiber, generally OM3 and other specifications, the color is blue.
Single mode fiber and multimode fiber are distinguished from each other in six aspects: core diameter, light source, bandwidth, sheath color, modal dispersion and price.
1. Core diameter
Single mode fiber: typical single-mode fiber is 8 and 10 μ m core diameter, cladding diameter is 125 μ m.
Multimode fiber: the general multimode fiber is 50 and 62.5 μ m core diameter, cladding diameter is 125 μ m.
2. Light source
Single mode fiber: with laser as light source, the price is more expensive than LED light source, the light generated by laser light source can be accurately controlled, with high power.
Multimode fiber: with LED as the light source, the light produced is scattered.
3. Bandwidth
Single mode fiber: the mode dispersion caused by multiple spatial modes is smaller than that of multimode fiber, so it has higher bandwidth.
Multimode fiber: it has larger core size, supports multiple transmission modes, and has higher modal dispersion and lower bandwidth than single-mode fiber.
4. Sheath color
Single mode fiber: yellow outer sheath.
Multimode fiber: orange or water green outer sheath.
5. Modal dispersion
Single mode fiber: the laser used to drive single-mode fiber produces a single wavelength of light, so its modal dispersion is smaller than that of multimode fiber.
Multimode fiber: due to the use of LED light source, multimode fiber dispersion limits its effective transmission distance, has higher pulse spread rate, limits its information transmission capacity.
6. Price
Single mode fiber: the price is lower than that of dual-mode fiber, but the equipment of single-mode fiber is more expensive than that of multi-mode fiber, and the cost is higher than that of dual-mode fiber.
Multimode fiber: the price is higher than that of single-mode fiber, and the equipment of multimode fiber is cheaper than that of single-mode fiber, so the cost of multimode fiber is far less than that of single-mode fiber.
Function of single mode fiber: in optical fiber communication, single mode fiber (SMF) is a kind of fiber that transmits optical signal directly in transverse mode. Single mode fiber can run at 100M / s or 1g / SDE data rate, and the transmission distance can reach at least 5km. Generally, single mode fiber is used for remote signal transmission.
Role of multimode fiber: multimode fiber (MMF) is mainly used for short distance optical fiber communication, such as in buildings or campus. The transmission speed is 100M / s and the transmission distance is 2km.
There are still many questions about the difference and application of these two types of fiber. Next, we will analyze the differences between single-mode fiber and multi-mode fiber from their basic structure, transmission distance, cost and other aspects.
1、 Comparison of basic structure between single mode fiber and multimode fiber
The basic structure of optical fiber is generally composed of outer sheath, cladding, core and light source
Color difference of outer sheath
In practical application, the outer sheath color of optical fiber can be used to quickly distinguish single-mode optical fiber from multi-mode optical fiber. According to the definition of tia-598c standard, single-mode optical fiber OS1 and OS2 adopt yellow outer sheath, multimode optical fiber om1 and OM2 adopt orange outer sheath, and OM3 and OM4 adopt water blue outer sheath (for non military purposes).
Core diameter difference
The core diameter of multimode fiber is usually 50 or 62.5 μ m, and that of single-mode fiber is 9 μ M. In view of this difference, single-mode fiber can only transmit 1310nm or 1550nm optical signal in a narrow core diameter, but the advantage of small core is that the optical signal propagates along a straight line in single-mode fiber without refraction, small dispersion and high bandwidth; multi-mode fiber has a wide core, which can transmit multiple modes at a given working wavelength, but at the same time, due to the small core, it can transmit multiple modes in multi-mode fiber There are hundreds of transmission modes, and the propagation constant and group rate of each mode are different, which makes the fiber narrow bandwidth, large dispersion and large loss.
Differences in light sources
There are usually two kinds of light sources: laser light source and LED light source. Laser light source is used for single-mode fiber and LED light source is used for multi-mode fiber.
2、 Comparison of transmission distance between single mode fiber and multimode fiber
Single mode fiber is suitable for long distance transmission, and multimode fiber is suitable for short distance transmission.
The construction of data center is mainly based on short-distance transmission. In the short-distance transmission environment, the performance of multi-mode fiber is consistent with that of single-mode fiber, but the cost is lower. At the same time, OM3 and OM4 multi-mode fiber can support higher speed. In the current high-speed network era, there is a lot of demand for multi-mode fiber.
3、 Cost comparison between single mode fiber and multimode fiber
As mentioned above, the cost of multimode fiber is lower than that of single-mode fiber, which is mainly due to the cost of equipment and hardware, such as the cost difference of light source and material.
Similarly, the cost difference between multimode fiber system and single-mode fiber system is similar, and the construction cost of multimode fiber system is lower than that of single-mode fiber system.
4、 Q & A of single mode fiber and multimode fiber
1. Can single mode fiber and multimode fiber be mixed?
In general, it can not. The transmission mode of single-mode fiber is different from that of multi-mode fiber. If two fibers are mixed or directly connected together, it will cause link loss and line jitter. However, single-mode and multi-mode links can be connected by single-mode conversion jumper.
2. Can multimode optical modules be used on single mode fibers? What about using single-mode optical modules on multimode fibers?
Multimode optical module cannot be used on single-mode optical fiber, which will cause large loss; single-mode optical module can be used on multi-mode optical fiber, but optical fiber adapter should be used to convert optical fiber type. For example, 1000base-lx single-mode optical module can operate on multi-mode optical fiber by using optical fiber adapter. Fiber adapter can also be used to solve the connection problem between single-mode optical module and multi-mode optical module.
3. How to choose single mode fiber and multimode fiber?
The selection of single-mode fiber and multi-mode fiber should be based on the actual transmission distance and cost. If the transmission distance is 300-400 meters, multimode fiber can be used. If the transmission distance reaches several thousand meters, single-mode fiber is the best choice.
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