What is fiber wavelength?

The light we are most familiar with is the light we can see with the naked eye. Our eyes are sensitive to violet light with wavelengths from 400nm to red light with wavelengths of 700nm. But for optical fibers that carry glass fibers, we use light in the infrared region, which is longer wavelengths and invisible to the naked eye. The use of these longer wavelengths is mainly due to the lower losses in the fiber. This article focuses on the wavelengths commonly used in fiber optics and why these wavelengths of light are used.

Fiber wavelength

Definition of wavelength

Actually, light is defined by its wavelength. Wavelength is a number that represents the spectrum of light, and each light's frequency, or color, has a wavelength associated with it. Wavelength and frequency are related. In general, shortwave radiation is identified by its wavelength, while longwave radiation is identified by its frequency.

Common wavelengths in fiber

Typical wavelengths are generally 800 to 1600nm, but by far the most commonly used wavelengths in fiber are 850nm, 1300nm and 1550nm. Multimode fiber is suitable for wavelengths of 850nm and 1300nm, while single mode fiber is best used for wavelengths of 1310nm and 1550nm. The difference between the wavelengths of 1300nm and 1310nm is only in the customary name. Lasers and light-emitting diodes are also used for light propagation in optical fibers. Lasers are longer for single-mode devices with wavelengths of 1310nm or 1550nm, while light-emitting diodes are used for multimode devices with wavelengths of 850nm or 1300nm.

Why choose these wavelengths?

As mentioned earlier, the most commonly used wavelengths in fiber are 850nm, 1300nm and 1550nm. But why did we choose these three wavelengths of light? This is because the optical signals of these three wavelengths have the smallest loss when transmitted in the optical fiber. They are therefore best suited as available light sources for transmission in optical fibers. The loss of glass fiber mainly comes from two aspects: absorption loss and scattering loss. Absorption losses occur mainly at a few specific wavelengths, which we call "water bands," and are mainly due to absorption by tiny water droplets in the glass material. The scattering is mainly caused by the bouncing of atoms and molecules on the glass.

Long wavelengths scatter much less, and that's what wavelength does most of all. From the table below we can clearly see three regions of low absorption and a curve that decreases scattering with increasing wavelength length. As you can see, in those three wavelength regions, the absorption is almost zero.

in conclusion

After reading this article, you may have some basic understanding of the wavelengths used in fiber optics. Since 850nm, 1300nm and 1550nm have relatively low wavelength losses, they are the best choice for fiber optic communications.