Achromatic Folded Optical Assembly for Triple-Pass Chromatic Correction
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Solution Overview
Problem
Optical systems suffer from chromatic aberrations, particularly lateral and longitudinal chromatic aberrations, when light of different wavelengths do not have a common focus, which is exacerbated in triple-pass folded systems.
Innovation Solution
An optical lens assembly with a folded optical path, incorporating a partial reflector and a reflective polarizer, is designed to reduce chromatic aberrations by reflecting and transmitting light of different wavelengths at different depths within the reflective polarizer, adjusting focal lengths to match, and using a multilayer optical film to compensate for wavelength differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a triple-pass folded optical system is used to increase field of view and magnification, then the optical performance is improved, but lateral and longitudinal chromatic aberrations are significantly worsened
Solution Approach 1:
The optical system is divided into multiple lens elements (first lens element, second lens element, third lens element) with different optical properties. Each element is optimized to contribute differently to the overall chromatic aberration correction, allowing the system to achieve low chromatic aberration in a triple-pass folded configuration while maintaining wide field of view and magnification capabilities
Solution Approach 2:
Different regions of the optical system are assigned different functions: the first lens element (with positive optical power) addresses longitudinal chromatic aberration, while the second and third lens elements (with negative optical power) address lateral chromatic aberration. This localized optimization of optical properties at different positions enables simultaneous correction of both chromatic aberration types
2Manufacturing precision
If conventional achromatic lens designs are used to reduce chromatic aberration, then chromatic performance is improved, but the designs do not effectively correct chromatic aberrations in triple-pass folded optical systems
Solution Approach 1:
The optical system is designed with specific optical power distributions and dispersion characteristics that dynamically adapt to the triple-pass folded configuration. The lens elements are optimized to provide different levels of chromatic correction at different passes through the system, enabling effective chromatic aberration reduction specifically for folded optical paths rather than conventional single-pass systems
Solution Approach 2:
The system uses lens elements with different Abbe numbers (V1, V2, V3) representing different optical materials or material compositions. By combining materials with different dispersion properties in a specific configuration, the system achieves chromatic aberration correction that is tailored for triple-pass folded optical systems, overcoming the limitations of conventional achromatic designs
3Volume of moving object
If the optical path is folded to reduce system size, then the physical dimensions are reduced, but chromatic aberrations are exacerbated
Solution Approach 1:
The optical system employs a folded configuration where the optical path is nested back on itself multiple times (triple-pass) within a compact volume. The lens elements are arranged to guide light through the system in a folded manner, achieving high magnification and wide field of view in a small form factor while the specific optical design compensates for the chromatic aberrations introduced by the folded path
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system achieves reduced lateral and longitudinal chromatic aberrations, with a lateral chromatic aberration ratio less than a factor of 2 across a 40-degree field of view and diopter variation less than 0.5 diopters, improving image clarity and reducing color fringing.
Implementation Method 1
a partial reflector and a reflective polarizer... reflecting and transmitting light of different wavelengths at different depths within the reflective polarizer
Implementation Method 2
the reflective polarizer has an optical reflectance of greater than about 60% for the incident light polarized along a first direction and an optical transmittance of greater than about 60% for the incident light polarized along a second direction, orthogonal to the first direction
Implementation Method 3
the lens assembly focuses the incident light on the display-side of the optical system and forms a first focused incident light at an average spacing T1 from the optical axis
Data Source
AI summary
An optical lens assembly includes an optical axis and two optical lenses having at least one curved major surface, a partial reflector disposed on a first major surface of the lens assembly, and a reflective polarizer disposed on a second major surface. For each of first and second visible wavelengths, and for unpolarized collimated light incident on the assembly from the viewer-side, the assembly focuses the incident light on the display-side, forming a first focused incident light at an average spacing T1 from the optical axis after the light passes through the assembly a first time, and a second focused incident light at an average spacing T2 from the optical axis after the light passes through the assembly three times, such that due to the difference between the first and second wavelengths, the first and second focused incident lights have respective lateral chromatic aberrations D1 and D2, D2/T2<D1/T1.