An introduction to the differences between singlemode and multimode fiber optics

      Fiber optic as a network transmission medium, is widely used in network cabling, the actual use, will come into contact with single-mode and multi-mode optical fiber, many people do not understand the differences between the two, resulting in the use of mixed. The following is a brief introduction to the difference between single-mode fiber and multi-mode fiber.
1. Single-mode fiber and multi-mode fiber similarities
      Single-mode fiber and multimode fiber structure is the same, are composed of three layers of transparent medium, from inside to outside, respectively, for the highest refractive index of the core, the lower refractive index of the cladding and the outside of the coating layer, due to the difference in the refractive index of the core and the cladding of the interface, which will produce a total reflection of the light, so that the light transmission in the core will not run to the outside. As shown in the figure below:

Figure 1 Structural section of optical fiber

2. The difference between single-mode fiber and multi-mode fiber
      A. Different core diameters
      Although the single-mode fiber and multimode fiber cladding diameter is the same, the diameter of the size of the 125μm, but the core diameter of the multimode fiber is much larger than the core diameter of the single-mode fiber, single-mode fiber core diameter is generally 9μm, while the core diameter of the multimode optical fiber is generally 50μm/62.5μm.

Figure 2 single-mode and multi-mode fiber core diameter difference comparison chart

      B. Different working wavelengths
      Single-mode fiber usually works in the 1310nm band and 1550nm band, while the multi-mode fiber works in the 850nm band.
      C. Different attenuation and dispersion
      Single-mode fiber attenuation is low, small dispersion, signal loss in the transmission process is small, not easy to distort. Multimode fiber attenuation is relatively high, dispersion is also more serious, limiting its transmission distance.
      D. Different transmission distances
      Single-mode fiber is suitable for long-distance transmission, usually used for 1KM-120KM transmission, while the dispersion of multi-mode fiber is serious, suitable for short-distance transmission, usually used for less than 1KM transmission.
      E. Different sheath colors
      Sheath color can be used to distinguish between single-mode fiber optic patch cords and multimode fiber optic patch cords, single-mode fibers with yellow outer sheath, multimode fibers according to the type of different types of sheaths, there are a variety of colors, OM1/OM2 multimode fibers with orange sheath, OM3 multimode fibers with lake blue sheath, OM4 multimode fibers with lake blue/purple sheath, OM5 multimode fibers with aqua green sheath.

Figure 3 Comparison of singlemode and multimode sheath colors

      3. Comparison of advantages and disadvantages
      A. Advantages and disadvantages of single-mode fiber
      Advantages of single-mode fiber: single-mode fiber attenuation and dispersion is small, the bandwidth is higher, suitable for large-capacity, long-distance communication.
Disadvantages of single-mode fiber: single-mode fiber is sensitive to pollution, requires high-precision connectors, and the light source process is complex, therefore, its installation and equipment costs are high.
      B. Advantages and disadvantages of multi-mode fiber
      Advantages of multimode fiber : multimode fiber core diameter, insensitive to pollution, simple connection, low cost of light source and equipment.
      Disadvantages of multimode fiber : multimode fiber attenuation and dispersion, can only be used in short-distance communication.
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