Optimized annular phase masks to extend depth of field

Abstract

A radially symmetric phase mask composed of several annular zones with equal area (called APM) was designed based on the incoherent imaging theory from Fourier Optics. The phase of any ring equals minus of the phase function caused by certain defocus. Another circularly symmetric phase mask similar to the APM (called MQPM) was proposed, except for the different phase function deriving from the quartic phase mask (QPM). For MQPM, there are two differences from an existing phase mask: the selection of the phase parameters and the method to divide the phase mask. An optimization model was developed to obtain optimized parameters of the phase masks. Numerical evaluations show that both APM and MQPM are less insensitive to defocus than QPM, and the defocused optical transfer functions with two phase masks are symmetric about the in-focus plane in the axial direction.

Theoretical and experimental analysis of co-designed binary phase masks for enhancing the depth of field of panchromatic cameras

“…Placing a phase mask in the aperture stop of an imaging system can enhance its depth of field (DoF), and this DoF extension capacity can be maximized by jointly optimizing the phase mask and the digital processing algorithm used to deblur the acquired image. This method, introduced by Cathey & Dowski with a cubic phase mask, 1,2 has been generalized to different mask models such as continuous rotationally symmetric phase masks, [3][4][5] polynomial phase masks, 6 or different types of binary phase masks. [7][8][9][10][11] The deblurring algorithm can be based on the Wiener filter 12,13 or neural networks.…”

Improved extension of depth-of-field performance by apodized wavefront coding

“…[1][2][3][4][5][6][7] Among these methods, Wavefront coding (WFC), which was proposed by Dowski and Cathey,8) has been shown to be effective for extending the DOF in many applications. [9][10][11][12][13] WFC involves combining the phase modulation of the pupil by inserting a special phase mask [14][15][16][17][18][19][20][21][22] with digital processing using a deconvolution filter. It has been pointed out that the original phase mask, i.e., a cubic phase mask (CPM) proposed by Dowski and Cathey, produces a significant number of artifacts in the reconstructed image and various new types of phase masks have been proposed so far to overcome the artifact problem.…”

Tunable extended depth of field using a liquid crystal annular spatial filter

“…Increasing the NA improves the system's resolution, however at the cost of lowering the DOF. In recent years many methods were suggested to bypass this problem by adding proper pupil phase masks to provide extended depth of field (EDOF) with sufficient resolution [1][2][3][4][5][6][7]. EDOF implementation may be "all-optical" or supported by image processing.…”

“…The second mask was of the form of the quartic phase mask (QPM) mask previously suggested in [3], which is parametric, with the parameters (a) and (b) may be calculated by minimizing a cost function to emphasize spectrum range, i.e., can be designed to prefer specific pattern within specific EDOF [3]. Thus, it can be used to realize few subcomponents for our "database."…”