According to the transmission mode of light in the fiber, it can be divided into: single-mode fiber and multi-mode fiber.

The core diameter of the multimode fiber is 50~62.5μm, the outer diameter of the cladding is 125μm, and the core diameter of the single-mode fiber is 8.3μm, and the outer diameter of the cladding is 125μm. The working wavelengths of the optical fibers are 0.85 μm for short wavelengths, 1.31 μm and 1.55 μm for long wavelengths. The fiber loss generally decreases with the wavelength, the loss of 0.85μm is 2.5dB/km, the loss of 1.31μm is 0.35dB/km, and the loss of 1.55μm is 0.20dB/km, which is the lowest loss of the fiber, the wavelength of 1.65 Losses above μm tend to increase. Due to the absorption effect of OHˉ, there are loss peaks in the range of 0.90~1.30μm and 1.34~1.52μm, and these two ranges are not fully utilized. Since the 1980s, single-mode fibers have tended to be used, and the long wavelength of 1.31 μm has been used first.