A modulator is an electronic or optical assembly with which an electrical or optical signal is superimposed with one or more signals. Modulators are used in communications engineering and optical transmission technology. The function performed by modulators is modulation.
In the case of communications engineering, a fundamental frequency, the transmission or carrier frequency, is superimposed with a low-frequency information signal. The information signal can be a voice, audio or video signal, a radar pulse or a data string. Depending on the modulation method, the carrier frequency is changed in its amplitude, frequency or phase in the rhythm of the superimposed signal frequency. Accordingly, the modulation methods are called amplitude modulation, frequency modulation and phase modulation. In principle, modulators work with non-linear characteristics where the carrier frequencies are mixed with the low-frequency signals.
Transferred to electro-optical modulators such as the electro- absorption mod ulator( EA) or the Mach-Zehnder mod ulator( MZM), the high frequency is replaced by a light beam whose intensity is changed with the transmission signal.