We know that optical modules can be divided into single-mode optical modules and multimode optical modules are usually marked on the module. Single mode to SM, for long-distance transmission, fiber color is yellow; multi-mode is MM, usually used for short-distance transmission, fiber color is orange. In addition to these, how can we distinguish between single-mode and multimode?

1. The wavelengths are different 

The general multi-mode light wavelength of 850nm, the single-mode optical wavelength is mainly 1310nm and 1550nm-based. Multi-mode optical module due to inter-mode dispersion is more serious, can only be used for short-range transmission (SR); and the single-mode optical module for LR, ER, ZR and other long-distance transmissions. Under normal circumstances, the transmission distance of 2km or less, known as the multi-mode module; transmission distance of 2km or more, known as the single-mode module.

2. The scopes of application are different

Multi-mode optical modules are used in networks with relatively low transmission rates and relatively short transmission distances, such as local area networks. These networks usually have multiple nodes, many joints, many detours, large amount of connectors and couplers, Fiber length using the number of light sources and other characteristics, the use of multi-mode optical module can effectively reduce network costs;

Single-mode optical module used for transmission distance is long, the transmission rate is relatively high lines, such as long-distance trunk transmission, metro network construction.

3. Different types of fiber

According to the transmission modes of light in the optical fiber, there are single-mode fiber and multimode fiber.

Multimode fiber (abbreviated MMF) fiber diameter of 50 / 125μm or 62.5 / 125μm two, their transmission distance is not the same. General gigantic environment 50 / 125μm can transmit 550m, 62.5 / 125μm can only pass 330M.

Single-mode fiber (abbreviated SMF) fiber diameter of 9 / 125μm. The main wavelength of single-mode fiber is 1310nm, 1550nm. Optical fiber loss is generally reduced with increasing wavelength, 1310nm loss of 0.35dB / km; 1550nm loss of 0.20dB / km.

Single-mode fiber is cheap, but single-mode equipment is much more expensive than its multimodal device. Single-mode devices can operate either on single-mode fiber or multimode fiber, while multimode devices are limited to multimode fiber operation.