Rotationally symmetric wavefront coding for extended depth of focus with annular phase mask

Abstract

Wavefront coding (WFC) with a cubic phase mask (CPM) for extended depth of focus (EDOF) has been studied since 1995. However, the asymmetric surface shape of a CPM has several disadvantages, such as necessity of a square aperture, directional artifacts in images, rotational adjustment during assembly, defocus-dependent lateral image displacement, and difficulty in fabrication. To overcome these disadvantages, we propose an annular phase mask (APM) with a rotationally symmetric form. An APM adds the phase of the parabolic profile in plural annuluses and phase steps between annuluses to the penetrating light. We confirmed an EDOF effect comparable to that of a CPM in our APM design by simulation. The depth of focus of a WFC system with the APM was estimated to be about 6.8 times larger than that of a conventional system. The effect observed in the experiments using a fabricated APM is consistent with the simulation result.

Metasurface optics for full-color computational imaging

“…After deconvolution, we can clearly make out each individual character, whereas the blue B is blurry and the red R is unintelligible in the image captured directly with the singlet lens. The deconvolved images do exhibit some erroneous horizontal and vertical lines arising from the asymmetric shape of the PSF, which can produce directional artifacts, but these can be corrected by more advanced deconvolution as well as by using a rotationally symmetric PSF (36). Figure 4B The scale bars are of length 20 μm.…”

Development of pupil divided optics with magnification correction for high NA oblique imaging

“…On the other hand, DOF expansion has been achieved with both computational imaging using multi aperture [5][6][7][8][9][10][11][12][13][14] or wavefront coding (WFC). 15,16) The computational imaging requires a large amount of data processing. Therefore, they are difficult to use for oblique imaging inspection in high throughput (∼100 MHz).…”

Compound eye image scanner optimally arranged for image combining and suppressing axial chromatic aberration by wavefront coding

“…15 Therefore, various patterns of axially symmetric modulated WFC have been proposed, including a logarithmic function, 16 a quartic function, 17,18 and an annular phase mask. 19 In this report, we present three key contributions: (a) a compound eye optical system can be applied to an image scanner product that requires compactness and high image quality, shown by specific design examples and the evaluation results of prototypes. (b) By applying a WFC technique to the compound eye optics, the imaging units can have good image quality despite their simple structure of just two plastic lenses.…”