Multimode and Single Mode Light Propagation

Multimode and Single Mode Light Propagation
Wavelengths – The light that is traveling through the core
Without getting into too much detail we need to talk about wavelengths. Just like copper cables carry different RF frequencies, fiber cable carries different frequencies of light or wavelengths. To keep it simple, think of the wavelength as a color of light and each color of light takes its own path down the core of the fiber and will not interfere with the other colors of light that might be traveling down the same fiber. (Basically, what we have just described is wavelength division multiplexing WDM or DWDM)

The light source determines the wavelength. Lasers can be tuned to send specific wavelengths down the fiber core. And since each wavelength takes a different path down the core of the fiber, some fiber types are better suited for some wavelengths. As you will see, Multimode Fiber transports light signals at different wavelengths than Single Mode Fiber.
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Standard Fiber Wavelengths
Multimode Fiber: 850nm and 1300nm
Single Mode Fiber: 1310nm and 1550nm

Note: Wavelength is measured in nanometers