Wave-front coding (WFC) is a well-known technique that can be used to extend the depth of field (DOF) of incoherent imaging systems. The phase masks make the optical transfer function drop significantly, and digital restoration must be used to obtain a clear image with a largely extended DOF.

According to the existing literature, in order to obtain satisfactory restoration results, the optical modulation transfer function (MTF) at the Nyquist frequency is required to be bigger than 0.1, which has already become a popularly accepted design constraint.

However, according to our experimental research reported in this paper, this requirement is overly strict.

To address the above-mentioned problems, ZHAO Hui’s research team from XIOPM proposed a novel method. By assembling one already fabricated WFC lens and another camera having physically higher resolution, the MTF of the newly assembled WFC system used in the experimentation has quite a low response at its Nyquist frequency.

The experimental results demonstrate that when the optical MTF value at the Nyquist frequency reaches the minimum value of about 0.05, visually satisfactory restoration results can still be obtained as long as the MTF is optimized to be highly insensitive to defocus and the corresponding SNR of the coded intermediate images goes beyond 20 dB at the same time.

The experimental results indicate that the overly strict constraint could be alleviated while designing a WFC system.

（Original research article " Applied Optics Vol. 58, Issue 35, pp. 9562-9569 (2019) https://doi.org/10.1364/AO.58.009562 "）