Complex wavefront sensing based on alternative structured phase modulation

Spatial light modulators (SLMs), which generate varying phase modulation, are widely used in coherent diffraction imaging. Random patterns are uploaded on the SLM to modulate the measured wavefront. However, a random pattern is highly complex and requires a reliable SLM. In addition, the uncorrelated terms generated from the random modulations need to be sufficiently captured using an imaging sensor with a high signal-to-noise ratio (SNR) to avoid stagnation during iterations. We propose an alternative structured phase modulation (ASPM) method. The modulations are composed of orthogonally placed phase bars that introduce uncorrelated modulations. The ASPM modulation can act as the phase grating; in addition, the modulated intensities are concentrated, which can be captured with a high SNR. The complexity of the ASPM patterns is significantly reduced, which is helpful for utilizing the SLM to generate reliable phase modulation.