Optical Device Extending Depth of Field via Phase Mask Design
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Solution Overview
Problem
Existing optical imaging systems face challenges in reducing image errors and distortions, such as lens aberrations and misfocus errors, while increasing the depth of field without compromising optical efficiency, and current methods like using phase masks are difficult to fabricate accurately, leading to high costs and fabrication errors.
Innovation Solution
A method is developed to design an optical device with a lens and microlens array by formulating a point spread function with rotationally symmetrical aberration coefficients, adding virtual phase mask coefficients to homogenize spherical spot sizes, and determining surface contours and sag heights based on aberration coefficients, eliminating the need for a real phase mask and simplifying fabrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If a phase mask with non-rotational surface is used to extend depth of field, then the depth of field is increased, but the fabrication difficulty and cost increase significantly
Solution Approach 1:
The patent applies asymmetry by using a non-rotationally symmetric phase mask design that intentionally introduces controlled asymmetric aberrations. This asymmetric structure is specifically engineered to extend the depth of field while managing the fabrication challenges through precise mathematical modeling of the phase coefficients.
Solution Approach 2:
The patent employs parameter changes by optimizing the phase coefficients of the phase mask to achieve the desired depth of field extension. By carefully adjusting these parameters, the system extends depth of field while attempting to balance fabrication feasibility through mathematical optimization.
2Duration of action of stationary object
If a complicated lens system is used to expand depth of field, then the depth of field is greatly expanded, but the system cost becomes very expensive
Solution Approach 1:
The patent extracts the depth of field extension function from a complicated multi-element lens system and implements it through a single phase mask element. This extraction allows depth of field extension without requiring a complex lens system, thereby reducing overall system complexity and cost.
Solution Approach 2:
The phase mask serves multiple functions: it extends the depth of field while maintaining acceptable image quality across a range of focal positions. This multi-functionality replaces what would traditionally require multiple lens elements, simplifying the overall system.
3Manufacturing precision
If the lens F-number is increased to reduce imaging errors, then lens aberrations are reduced, but the optical efficiency decreases
Solution Approach 1:
The phase mask acts as an intermediary element that modifies the wavefront to correct imaging errors and extend depth of field. This intermediary component allows the system to maintain lower F-numbers (higher optical efficiency) while still achieving reduced imaging errors through the phase correction it provides.
Solution Approach 2:
The patent uses parameter changes in the phase mask design to control the point spread function and optimize the balance between imaging error reduction and optical efficiency. By adjusting the phase coefficients, the system can achieve acceptable image quality at lower F-numbers than traditional systems.
Data Source
AI summary
A method for designing an optical device which includes a lens and a microlens array is disclosed. A point spread function (PSF) of the lens including rotationally symmetrical aberration coefficients is formulated, wherein the PSF presents various spherical spot sizes. A virtual phase mask having phase coefficients is provided and the phase coefficients are added to the PSF of the lens, such that the various spherical spot sizes are homogenized. The virtual phase mask is transformed into a polynomial function comprising high and low order aberration coefficients. A surface contour of the lens is determined according to the rotationally symmetrical aberration coefficients and the low order aberration coefficients, and a sag height of each microlens in the microlens array is determined according to the high order aberration coefficients. An optical device using the design method is also disclosed.