Multimode fiber refers to a graded index multimode fiber with a core of 62.5μm or 50μm. Multimode fiber can be divided into five categories: OM1, OM2, OM3, OM4, and OM5, corresponding to different transmission rates and transmission distance.

Single-mode fiber is a fiber that can transmit only one mode of light at a specified wavelength, and its core is 9μm. At present, common single-mode fibers are G.652, G.653, G.654, G.655, G.657.

Generally, an optical link requires two optical fibers to complete the entire transmission process. The matching from the transmitting end to the receiving end is called polarity. In ordinary wiring systems, single-core connectors are usually used, which are easy to match. However, for MPO and MTP high-density wiring systems, the issue of polarity must be paid close attention to.