The contrast has its maximum value when using phase shifts of 0° and 180° in terms of electrical
and optical signal . Depending on modulation waveform, an ideal device can have a maximum
contrast of 100%, that is, all photo generated charge carriers contribute to the phase measurement
since they are properly distributed to the corresponding readout channels (perfect device and system). Therefore, the contrast reflects the separation ability of the device in terms of charge carriers generated by correlated light. By definition the contrast is significantly affected by the signal sum, therefore determination of the device contrast is only valid with out any uncorrelated illumination , and so the measurement must be carried out with a modulated light signal only.