Single-mode optical fiber can only transmit single-mode signals, while multimode optical fiber can transmit multimode signals, multimode optical fiber (Multimode optical fiber = MMF): As the name suggests, it is optical fiber that is capable of transmitting many modes of electromagnetic waves (in this case, light waves); Because there are multiple modes of transmission, there is a large dispersion between modes and a small amount of information can be transmitted; The core of multimode fiber is larger, generally 50um, and the numerical aperture is about 0.2. The number of molds depends on the diameter of the fiber core, numerical aperture and wavelength.
Single mode fiber (Single-mode fiber = SMF):They can transmit only one pattern of signal waves, but they must be qualified: it seems to me that the textbook talks about something called uniformization frequency, and the fiber cores need to be especially thin, preferably three or four times the working wavelength; Therefore, single-mode light is much thinner in form than multi-mode fibers; Monomode optical fiber transmits only one mode, so there is no mode dispersion.
Multi-mode fibers are used for small capacity, short-range systems, single-mode fiber is used for backbone, high-capacity, long-range systems Single-mode fiber core diameter is generally 9 / 125 while multi-mode is 50 / 125 or 62.5 / 125.
Monomode and multimode are relative to specific wavelengths, and the same fiber may be monomode or multimode at different wavelengths.Light does not have a single multimode, the light source has a single longitudinal model ~ (dfb) and a multi-longitudinal model (fp). Multi-mode fibers are finer than single-mode fiber in fiber diameter, the single-mode 652 is 62.5 / 125, while multi-mode fiber is 50 / 125 and 62.5 = 125.In terms of price, multi-modes are generally 1.5 to 2 times the number of single-modes. From the practical application, multi-models are basically used in data access cables. The biggest disadvantage of multi-mode compared to single-mode is inter-mode dispersion (because the rate of the same light in different modes is different).
In China, 62.5 / 125 multi-mode fiber is mainly used, and as for the difference between the two, it seems that the purpose of the cable is different, with 50 percent used for indoor fiber optics.
Single-mode optical fiber transmits only one mode of the base model, and multi-mode can transmit multiple modes. Single models are mainly used on long-distance main lines, and multimodels are used in local areas. Some people said before that the single mold is much finer than the multi mold, which is actually not true. The diameter of both fiber cladding is 125 but the core diameter is different. The single mold is 9 and the multi mold is generally used in 50 and 62.5. In general, a single model does not directly connect to a multi-model because it is through a device conversion.
There are two types of optical fibers: multi-mode fibers and single-mode fiber, and the difference between multi-mode and single- mode fibers is mainly that the transmission mode of light is different, and of course the bandwidth capacity is also different. The multi-mode optical fiber has a large diameter, and beams of different wavelengths and phases are constantly reflected forward along the fiber wall, causing dispersion and limiting the transmission distance and bandwidth between the two repeaters. The bandwidth of multi-mode fiber is about 2.5Gbps. The diameter of single-mode optical fiber is small, and light travels in a straight line in it and is rarely reflected, so the dispersion is reduced, the bandwidth is increased, and the transmission distance is also increased. However, the corresponding optical end equipment is relatively expensive, and the bandwidth of single-mode fiber exceeds 10Gbps.
Multimode fibers are more affected by pulsed signal expansion (scattering) in higher modes, while singlemode fibers better solve the problem of intermode scattering. SMF CORE 8.3-9.3 um. MFD is usually 9.3 um.
