In particular, multi-level amplitude modulation schemes, which read and write data pages with three or more amplitude gradations, have the advantage of allowing existing optical systems to be used ...

See modulation and carrier. Vary the Amplitude In AM modulation, the voltage (amplitude) of the carrier is varied by the incoming signal. In this example, the modulating wave implies an analog signal.

Offset Quadrature Amplitude Modulation (OQAM): A modulation technique that staggers the in-phase and quadrature components in time, reducing interference and improving spectral efficiency.