Optimized annular phase masks to extend depth of field

Area of Science:

• Optics and Optical Engineering
• Fourier Optics
• Image Science

Background:

• Defocus is a common aberration in optical imaging systems, degrading image quality.
• Existing phase masks, such as the quartic phase mask (QPM), aim to mitigate defocus effects.
• Radially symmetric phase masks offer potential for improved performance in incoherent imaging.

Purpose of the Study:

• To design and evaluate novel radially symmetric phase masks for enhanced defocus control.
• To compare the performance of the proposed annular phase mask (APM) and modified quartic phase mask (MQPM) against existing QPM.
• To investigate the axial symmetry of the defocused optical transfer functions (OTFs) for the new designs.

Main Methods:

• Design of APM based on incoherent imaging theory and Fourier Optics, utilizing annular zones with equal areas.
• Proposal of MQPM with a modified phase function derived from QPM, differing in parameter selection and mask division.
• Development of an optimization model to determine optimal phase mask parameters.
• Numerical evaluation of APM and MQPM performance, including analysis of defocused OTFs.

Main Results:

• Both APM and MQPM demonstrate reduced sensitivity to defocus compared to QPM.
• The defocused optical transfer functions for APM and MQPM exhibit symmetry around the in-focus plane along the axial direction.
• The proposed phase masks maintain image quality under defocused conditions more effectively than QPM.

Conclusions:

• APM and MQPM represent effective designs for improving defocus robustness in incoherent imaging systems.
• The axial symmetry of defocused OTFs indicates stable imaging performance across a range of defocus values.
• These novel phase masks hold promise for applications requiring high image quality and stability in the presence of defocus.