What is the wavelength of an optical fiber?

- Nov 11, 2020-

Definition of wavelength

In fact, light is defined by its wavelength. Wavelength is a number representing the spectrum of light. The frequency, or color, of each light has a wavelength associated with it. Wavelength and frequency are related. Generally speaking, short-wave radiation is identified by its wavelength, while long-wave radiation is identified by its frequency.

Common wavelengths in optical fibers

The typical wavelength is generally 800 to 1600nm, but as of now, the most commonly used wavelengths in optical fibers 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 wavelength of 1300nm and 1310nm is only in the customary name. Lasers and light-emitting diodes are also used for light propagation in optical fibers. The laser is longer than a single-mode device with a wavelength of 1310nm or 1550nm, while a light-emitting diode is used for a multimode device with a wavelength of 850nm or 1300nm.


Why choose these wavelengths?

As mentioned before, the most commonly used wavelengths in optical fibers are 850nm, 1300nm and 1550nm. But why do we choose these three wavelengths of light? It is because the optical signals of these three wavelengths have the least loss when transmitted in the optical fiber. Therefore they are most suitable 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 loss mainly occurs at a few specific wavelengths that we call "water bands", mainly due to the absorption of trace water droplets in the glass material. The scattering is mainly caused by the rebound of atoms and molecules on the glass.

The scattering of long waves is much smaller, which is the main effect of wavelength. From the table below, we can clearly see three low-absorption regions and a curve where the scattering decreases as the wavelength length increases. As you can see, in those three wavelength regions, the absorption is almost zero.

Conclusion

Because the wavelength loss of 850nm, 1300nm and 1550nm is relatively low, they are the best choice for optical fiber communication.