Intermodulation, also known as mixing, is a fiber nonlinearity mechanism caused by the power-dependent refractive index of glass. It occurs when two or more optical signals of different frequencies are transmitted through an optical fiber cable, causing them to interact with one another and produce new signals at different frequencies. This phenomenon is often referred to as four-wave mixing, due to the fact that four waves are involved in the process.
The new signals generated by intermodulation are known as “intermodulation products” and they can interfere with the original signals, causing significant degradation of signal quality. This is especially pronounced in cables where two or more signals are launched at similar power levels and frequencies. In this situation, the intermodulation products are generated with even higher power levels, making them even more disruptive.
Intermodulation can also cause other problems, such as signal crosstalk and signal distortion. Signal crosstalk occurs when the intermodulation products interfere with the signals in adjacent cables, resulting in a decrease in signal quality. Signal distortion occurs when the intermodulation products cause the signal to become distorted and distorted signals may cause further distortion and interference.
In order to reduce the effects of intermodulation, it is important to choose cables with low nonlinearity characteristics. This can be achieved by using low-loss fiber cables and ensuring that the fiber has a high refractive index. Furthermore, it is important to ensure that all signals being transmitted through the cable are launched at comparable power levels and frequencies. This will help to reduce the power levels of the intermodulation products, making them less disruptive.