We propose a dither-free 8-phase-shift-keying (8PSK) generator control scheme for adjusting the bias voltage of Mach–Zehnder modulator (MZM) and the electrical driver signals of two cascaded phase modulators (PMs). The control module includes a delay-line interferometer (DLI), a balanced photo-detector (BPD), and asynchronous sampling data processing. Both analysis and simulation results show that the bias voltage and the driver signal amplitude control can be achieved independently between these cascaded modulators with only one tap point and one control configuration. Finally, the influence of the bit number of A/D converter (ADC) for asynchronous sampling is also discussed for the practical implementation.