Hybrid diffractive optics (DOE & refractive lens) for broadband EDoF imaging.

In the considered hybrid diffractive imaging system, a refractive lens is arranged simultaneously with a multilevel phase mask (MPM) as a diffractive optical element (DOE) for Achromatic Extended-depth-of-field (EDoF) imaging. This paper proposes a fully differentiable image formation model that uses neural network techniques to maximize the imaging quality by optimizing MPM, digital image reconstruction algorithm, refractive lens parameters (aperture size, focal length), and distance between the MPM and sensor. Firstly, model-based numerical simulations and end-to-end joint optimization of imaging are used. A spatial light modulator (SLM) is employed in the second stage of the design to implement MPM optimized at the first stage, and the image processing is optimized experimentally using a learning-based approach. The third stage of optimization is targeted at joint optimization of the SLM phase pattern and image reconstruction algorithm in the hardware-in-the-loop (HIL) setup, which allows compensation for a mismatch between numerical modeling and the physical reality of optic and sensor. A comparative analysis of the imaging accuracy and quality using the optical parameters is presented. It is proved experimentally, first time to the best of our knowledge, that wavefront phase modulation can provide imaging of advanced quality as compared with some commercial multi-lens cameras.