E/O converter
Electro-optical converters (E/O converters) convert electrical signals into light signals. Light-emitting diodes and lasers are used for this conversion in communications technology. The conversion of the electrical signals into light signals can be done directly in the laser or the light-emitting diode, but it can also be done indirectly via an external modulator such as a Mach-Zehnder modulator( MZM).
In the first case, we speak of direct modulation of the optical signal, in the other case of external modulation. In this method, the modulator receives a light beam with constant energy from the laser, which is then modulated with the electrical signal in the modulator.
According to the method of external light modulation, the electro- absorption modulator( EA) also works.
Only digitally operating modulation techniques are used as modulation techniques. In addition to On/Off modulation - On stands for light on and corresponds, for example, to a logic "1" and Off to logic "0" - various manufacturers of optical transmitters rely on pulse width mod ulation( PWM) and pulse frequency modulation( PFM). In addition, combinations of several modulation methods are also used.