Characteristics of multimode optical fiber

The low transmission rate and short transmission distance can precisely utilize the bandwidth characteristics and transmission losses of multimode fiber, which are not as good as those of single-mode fiber. But single-mode fiber is cheaper and performs better than multimode fiber, why not use single-mode fiber in the network? This is because in the above network characteristics, more detours result in greater losses; If there are many nodes, optical power splitting will be frequent, which requires sufficient optical power transmission inside the fiber optic cable. Multimode fiber has a thicker core diameter and larger numerical aperture than single-mode fiber, and can couple more optical power from the light source. The number of connectors and couplers used in the network is large, and single-mode fiber passive devices are more expensive than multi-mode fibers. They are also relatively precise and have smaller tolerances, making operation less convenient and reliable than multi-mode devices. Single mode fiber can only use lasers (LDs) as light sources, which are much more expensive than the light-emitting diodes (LEDs) used in multimode fiber. Especially for networks with small scales and a large number of light sources used per unit fiber length, a single light source may be used for several hundred kilometers in the trunk line, while each network with tens or even several kilometers has its own independent light source. If the network uses single-mode fiber with a laser, the overall cost of the network will be significantly increased. Vertical cavity surface emitting lasers (VCSEL) have been commercially available at a price similar to LEDs. Their circular beam cross-section and high modulation rate compensate for the shortcomings of LEDs, making multimode fiber applications in networks more vibrant. From the above analysis, it is not difficult to see that considering single-mode fiber as having high bandwidth and low loss, and being able to be used in a network in one go, is not comprehensive. Corning Inc. calculated and compared the system costs of using single-mode fiber and multi-mode fiber in the network, and found that the network cost using single-mode fiber is four times that of multi-mode fiber. The system cost using 62.5 μ m and 50 μ m multimode fibers is the same, with the difference being the different types of connectors. The cost of using a plug and play connector system without metal hoops (multimode system B) can be reduced by half compared to connectors that use metal hoops for screwing, such as FC type (multimode system A).