MM fiber Concept
MM fiber is a fiber that transmits multiple modes at a given working wavelength. When the geometric size of the fiber is much larger than the wavelength of the light wave, there will be dozens or even hundreds of propagation modes in the fiber. Different propagation modes have different propagation velocities and phases, resulting in time delay and widening of optical pulses after long-distance transmission. Therefore, the bandwidth of MM fiber will be narrowed and its transmission capacity will be reduced, so MM fiber is only suitable for optical fiber communication with small capacity.
SM fiber Concept
Generally, when V is less than 2.405, only one wave peak passes through the fiber, so it is called a SM fiber. Its core is very thin, about 8-10 microns, and the modal dispersion is very small. The main factor affecting the bandwidth of optical fiber transmission is various dispersion. The dispersion of SM fiber is small, so it can transmit light over a long distance with a wide frequency band, so SM fiber is especially suitable for large-capacity optical fiber communication.
Differences between SM fiber and MM fiber
1. Appearance color
The most obvious difference between SM fiber and MM fiber is the color of the outer jacket. The SM fiber patch cord OS2 is yellow, while the MM fiber OM1 and OM2 is orange outer jacket, OM3 is aqua outer jacket, and OM4 is Purple.
2. Fiber diameter
The core diameter of MM fiber is generally 50µm (OM1) or 62.5µm (OM2, OM3, OM4), and the core diameter of SM fiber is 9µm (OS2).
3. Light source
The light source of SM fiber transmission is laser, and the light source of MM fiber transmission is LED.
MM fiber narrows the bandwidth due to modal dispersion, while SM fiber allows only one mode to propagate in the fiber, and the rest of the high-order modes are all cut off, avoiding the problem of modal dispersion, so SM fiber has a very wide bandwidth.
The price of MM fiber is cheaper than that of SM fiber. Because MM fiber is suitable for short-distance transmission and relatively low cost, it is widely used in data centers, while SM fiber is suitable for long-distance transmission,so it is mainly used in backbone network and metropolitan area network.
6. Transmission distance
The transmission distance of MM fiber is within 2KM, while the transmission distance of SM fiber can reach hundreds of kilometers.
7. Application scenarios
SM fiber is mainly used in metropolitan area network, backbone network, PON and other scenarios, while MM fiber is mainly used in enterprise, data center and other scenarios.
In general, SM optical modules need to be used with SM fiber patch cord, and MM optical modules need to be used with MM fiber patch cords. In addition, indoor and short-distance applications are dominated by MM fibers, and outdoor and long-distance applications are dominated by SM fibers.