With the development of optical communication and data centers, the application of optical modules is becoming more and more extensive. The type of optical modules and the transmission of data are also increasingly diverse. 40G optical modules, 100G optical modules, single-mode optical modules, multi-mode optical modules, and so on. Today, I will introduce you to the single-mode optical module and the multi-mode optical module. What is the difference between the two?
First, let's take a look:
What is an optical module?
The optical module is composed of an optoelectronic device, a functional circuit, an optical interface, and the like, and the optoelectronic device includes two parts, a transmitting and receiving device.
Simply put, the function of the optical module is photoelectric conversion, and the transmitting end converts the electrical signal into an optical signal. After transmitting through the optical fiber, the receiving end converts the optical signal into an electrical signal.
What is a single mode optical module?
Single mode is expressed in SM and is suitable for long distance transmission;
What is a multimode optical module?
Multimode is expressed in MM and is suitable for short-distance transmission.
What is the difference between the two?
(1) Different wavelengths
The operating wavelength of a multimode optical module is generally 850 nm, and the operating wavelength of a single mode optical module is generally 1310 nm and 1550 nm.
(2) Different transmission distances
Single-mode optical modules are often used for long-distance transmission with transmission distances of 150 to 200 km. The multimode optical module is used for short-distance transmission with a transmission distance of up to 5km.
(3) Different fiber types
A single mode in an optical module actually refers only to the type of fiber. According to the transmission mode of the optical module in the optical fiber, it can be classified into a single mode fiber and a multimode fiber.
The multimode fiber is abbreviated as MMF, and the fiber diameter is generally 50/125 μm or 62.5/125 μm.
The single mode fiber is referred to as SMF, and the fiber diameter is 9/125 μm.
(4) different light sources
The light source of the multimode optical module is a light emitting diode or a laser, and the light source of the single mode optical module is an LD or a LED with a narrow spectral line.
(5) Different application scope
Multi-mode optical modules are mostly used for short-distance transmission such as SR. There are many nodes and connectors in this type of network, and the cost can be reduced by using multi-mode optical modules.
Single-mode optical modules are mostly used in lines with relatively high transmission rates, such as metropolitan area networks.
In addition, multimode devices can only operate efficiently on multimode fibers, while singlemode devices operate efficiently on both single-mode and multimode fibers.
(6) different costs
The single-mode optical module uses twice as many components as a multimode optical module, so the overall cost of a single-mode optical module is much higher than that of a multi-mode optical module.
Through the above, there is a certain understanding of the difference between the single mode optical module and the multimode optical module.
However, there are some notes on the use of optical modules that need attention:
1: Can a high-rate optical module be used as a low-rate optical module?
This is not possible. High-rate optical modules are used when low-rate optical modules are used, although some are sometimes compatible, but some are compatible.
2: Can a single-mode fiber be plugged into a multimode optical module?
No. The single mode fiber is plugged into the multimode optical module and the link cannot be connected. The divergence angle of the optical signal emitted by the multimode optical module is large, the aperture of the single mode fiber is small, the light running into the optical fiber is too small, and the transmission cannot be long distance, and the length of the single mode fiber is long, and the optical signal is not attenuated until the end point.
3: Can multimode fiber be plugged into a single mode optical module?
The laser emitted by the single-mode optical module can be completely inserted into the optical fiber, but it is transmitted in multi-mode in the optical fiber, and the dispersion is relatively large, and short-distance transmission is possible. However, the optical power of the receiving end is increased, which may cause the optical power of the optical module at the receiving end to be overloaded. Therefore, it is recommended that the single-mode optical module use only single-mode optical fibers, and try not to use multi-mode optical fibers.
4: Can optical modules with different transmission distances be docked?
Not recommended. The optical module requires peer-to-peer use. For example, the transmission rate, transmission distance, transmission mode, and working wavelength of the optical module at the transmitting end and the receiving end must be the same. The optical module interface indicators of different transmission distances are very different, and the optical module price with a long transmission distance is different. Also high. For those who do have the demand, the docking can be achieved by matching the appropriate light decay, which is determined according to the actual situation of the network.
5: Under what circumstances do you need to use light decay?
When the optical power of the peer end is greater than the upper limit of the received optical power of the local optical module, you need to connect the optical fading on the link. After the optical signal is properly attenuated, connect the local optical module. When the long-distance optical module is used for short-distance applications. Use light attenuation adaptation, especially when self-looping, so as not to burn out the optical module.
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