Complex modulation Diffractive Optical Elements implemented in a single Spatial Light Modulator

Spatial light modulators (SLMs) are optoelectronic devices that spatially modulate the properties of an incident electromagnetic field, such as its amplitude, phase, or polarization. They are used to generate dynamic Diffractive Optical Elements (DOEs), which are normally configured as pure-amplitude or pure-phase DOEs. In this work, we propose to generate complex modulation with a single SLM for optimizing the performance of DOEs. For that, we fill, as evenly as possible, the Argand plane, representing the complex amplitude of the DOE, with the modulation curve provided by the SLM and the polarization plates used. Also, we modify the Iterative Fourier Transform Algorithm to design complex DOEs and implement them in the SLM that works in an amplitude-phase configuration. For the simulations, we have considered that the modulation curves are spiral-shaped. We have verified that their far-field diffraction patterns present more uniformity, less background noise, and higher diffraction efficiencies than when pure-phase configuration is used. For the experimental verification, we have calibrated a LCoS SLM and optimized the azimuths of the polarizers and quarter-wave plates, placed before and after the SLM, to obtain the optimal modulation curve. The diffraction pattern generated by the studied complex DOEs presents a 32% increase in diffraction efficiency and a reduction of 85% in background noise compared to the phase DOE.