Binary-to-Quaternary ASK Encoding in the Optical Domain With Semiconductor Optical Amplifiers

Quaternary amplitude-shift-keying signal is all-optically generated from binary signals exploiting gain compression in two semiconductor optical amplifiers. The scheme is suitable for phase-control-free all-optical digital-to-analog conversion. Only two semiconductor amplifiers, a single optical filter, and no assist probe light are required for 2-bit operation. In addition, the input wavelength is preserved at the output of the device. Dynamic operation is experimentally demonstrated. The quality of the level-converted signal is confirmed by the high Q -factor of the output eye diagrams.