Differences and applications between multimode fiber and single-mode fiber

1、 Multimode fiber

When the geometric size of the optical fiber is much larger than the optical wavelength, there will be dozens or even hundreds of propagation modes in the optical fiber. Different propagation modes have different propagation speeds and phases, resulting in time delay and optical pulse broadening after long-distance transmission. This phenomenon is called mode dispersion of optical fiber. Mode dispersion will narrow the bandwidth of multimode fiber and reduce its transmission capacity. Therefore, multimode fiber is only suitable for optical fiber communication with small capacity

2. Single mode fiber

When the geometric dimension of the optical fiber can be close to the optical wavelength, the optical fiber only allows one mode to propagate in it, and all the other high-order modes are cut off. Such an optical fiber is called single-mode optical fiber. Because it has only one mode of propagation and avoids the problem of mode dispersion, single-mode fiber has a very wide bandwidth and is especially suitable for high-capacity optical fiber communication.

3、 Differences between multimode fiber and single-mode fiber

1. Appearance diameter

From the aspect of appearance, the conventional resolution method is; The Yellow optical fiber line is generally a single-mode optical fiber, and the orange or gray optical fiber line is generally a multi-mode optical fiber. The difference between the two in the cable core is that the multi-mode cable core size is 50.0 μ M and 62.5 μ m； Single mode is 9.0 μ m。

2. Transmission mode

Multimode fiber: it can transmit optical signals with a wavelength of more than 0 nm or 1310 nm, and can transmit multiple modes at a given working wavelength.

Single mode fiber: it transmits optical signals with a wavelength of 1310nm or 1550nm. Single mode fiber has only one transmission mode.

3. Emission light source

Multimode optical fiber: generally, LED is used as the light source, and LED is commonly used as the light source. The size of coupling parts is well matched with multimode optical fiber.

Single mode fiber: generally, solid-state laser is used as the light source, and LD or LED with narrow spectral line is commonly used as the light source. The size of coupling part is well matched with single-mode fiber.

4. Dispersion bandwidth

Multimode fiber: large core diameter and multiple transmission modes; LED light sources are often used to create a series of wavelengths propagating at different speeds, making the transmission band very narrow, which will lead to multimodal dispersion, so the modal dispersion is large and the loss is large, which limits the effective transmission distance of multimode fiber.

Single mode fiber: the core diameter is small and only transmits the main mode; The laser used to drive single-mode fiber produces a single wavelength of light, and the modal dispersion is much smaller than that of multimode fiber, which can almost avoid modal dispersion, making the transmission frequency band very wide and the transmission capacity very large, which is suitable for long-distance transmission.

5. Price

Multimode fiber can support multiple optical modes, and its price is higher than that of single-mode fiber.

However, in terms of equipment, because single-mode fiber usually adopts solid-state laser diode, the price of optical transceiver equipment is high. At this time, the cost of establishing network with single-mode fiber is relatively high.

4、 How to select optical cable?

The selection of optical cable not only depends on the number of optical fiber cores and types of optical fibers, but also the structure and outer sheath of optical cable according to the service environment of optical cable.

1. Loose sheathed armored optical cables should be used when outdoor optical cables are directly buried. When overhead, loose sleeve optical cable with black PE outer sheath with two or more stiffeners can be selected.

2. When selecting optical cables used in buildings, tight sleeved optical cables shall be selected, and attention shall be paid to their flame retardant, toxic and smoke characteristics. Generally, the type of flame retardant but with smoke or combustible and non-toxic type can be selected in the pipeline or forced ventilation. The type of flame retardant, non-toxic and smokeless should be selected in the exposed environment.

3. When laying cables vertically or horizontally in the building, tight sleeved optical cables, distribution optical cables or branch optical cables commonly used in the building can be selected.

4. Single mode and multi-mode optical cables are selected according to the network application and optical cable application parameters. Generally, multi-mode optical cables are mainly used for indoor and short-distance applications, and single-mode optical cables are mainly used for outdoor and long-distance applications.

5、 What is the difference between multimode fiber transceiver and single-mode fiber transceiver?

The multi-mode transceiver receives multiple transmission modes, and the transmission distance is relatively close.

The single-mode transceiver receives only a single mode. The transmission distance is relatively long.

Price: multi-mode is cheap, single-mode is expensive

Distance: less than 2km for multi-mode and about 100km for single-mode

Wavelength: multi-mode, multi-mode, 1310 / 1550nm

Note: multimode transceiver corresponds to multimode optical fiber, single-mode corresponds to single-mode, and cannot be mixed.