  Lensless imaging is a popular research field for the advantages of small
size, wide field-of-view and low aberration in recent years. However, some
traditional lensless imaging methods suffer from slow convergence, mechanical
errors and conjugate solution interference, which limit its further application
and development. In this work, we proposed a lensless imaging method based on
spatial light modulator (SLM) with unknown modulation curve. In our imaging
system, we use SLM to modulate the wavefront of object, and introduce the
ptychographic scanning algorithm that is able to recover the complex amplitude
information even the SLM modulation curve is inaccurate or unknown. In
addition, we also design a split-beam interference experiment to calibrate the
modulation curve of SLM, and using the calibrated modulation function as the
initial value of the expended ptychography iterative engine (ePIE) algorithm
can improve the convergence speed. We further analyze the effect of modulation
function, algorithm parameters and the characteristics of the coherent light
source on the quality of reconstructed image. The simulated and real
experiments show that the proposed method is superior to traditional mechanical
scanning methods in terms of recovering speed and accuracy, with the recovering
resolution up to 14 um.
