Anamorphic Diffractive Lens Aberration Control
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Solution Overview
Problem
Optical scanners used in electrophotographic image forming apparatuses face challenges in achieving good performance when evaluated at a wavelength different from the actually used wavelength, due to issues with spherical aberration and the availability of interferometers with specific wavelengths.
Innovation Solution
The optical scanner incorporates an anamorphic condensing lens with a diffractive lens structure, where the optical path length is defined by a function of height, and specific coefficients are adjusted to suppress spherical aberration, ensuring good performance at both the actual and evaluation wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an anamorphic condensing lens is designed and evaluated at a wavelength of 790 nm, then the lens performance is optimized for the actual application wavelength, but it becomes difficult to obtain an interferometer with a light source for emitting a light beam of this wavelength for accurate evaluation
Solution Approach 1:
The patent changes the evaluation wavelength parameter from 790 nm to 633 nm by introducing a wavelength conversion coefficient k=0.8. This allows the lens to be evaluated at a commercially available He-Ne laser wavelength while still predicting its performance at the actual 790 nm application wavelength through the relationship φ1(h) = k·φ2(h).
Solution Approach 2:
The patent introduces a wavelength conversion coefficient k as an intermediary parameter that bridges the gap between the evaluation wavelength (633 nm) and the application wavelength (790 nm). This coefficient enables indirect evaluation of the lens performance at the actual operating wavelength using standard evaluation equipment.
2Manufacturing precision
If a fourth- or higher-order term of the phase function is introduced in the lens surface structure equation, then the lens can correct wavefront aberration, but a change in spherical aberration occurs due to wavelength difference between evaluation and actual use
Solution Approach 1:
The patent applies parameter changes by scaling the phase function coefficients with the wavelength conversion coefficient k. The relationship φ1(h) = k·φ2(h) ensures that the fourth- and higher-order terms that correct wavefront aberration at 633 nm are appropriately scaled to maintain their effectiveness at 790 nm, preventing spherical aberration changes.
3Reliability
If an anamorphic condensing lens is designed to work at 790 nm, then it achieves good performance for photoconductor drum sensitivity, but standard interferometers with He-Ne laser (633 nm) cannot accurately evaluate its performance
Solution Approach 1:
The patent uses parameter transformation by introducing the wavelength conversion coefficient k=0.8 to relate the phase functions at different wavelengths. This allows standard interferometers evaluating at 633 nm to provide accurate predictions of performance at 790 nm through the scaled relationship, resolving the mismatch between evaluation and application wavelengths.
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
This configuration effectively suppresses wavefront aberration in both the main and sub-scanning directions, allowing the optical scanner to maintain performance even when evaluated at a different wavelength, such as using a He–Ne laser for a wavelength of 633 nm to simulate performance at 790 nm.
Implementation Method 1
The anamorphic condensing lens has a diffractive lens structure at least in one lens surface thereof, and a length of an optical path increased by the diffractive lens structure φ [rad] is defined by an equation below by a function of a height h from an optical axis
Implementation Method 2
the incident optical system includes an anamorphic condensing lens which has different powers with respect to the main scanning direction and a sub-scanning direction
Data Source
AI summary
An optical scanner is configured such that an anamorphic condensing lens in an incident optical system has a diffractive lens structure at least in one lens surface thereof, and a length of an optical path increased by the diffractive lens structure φ [rad] is defined by an equation below by a function of height h from an optical axis: φ(h)=M(P2·h2+P4·h4+ . . . ), where Pn is a coefficient of an nth-order term of the height h (n is an even number), and M is a diffraction order, that the lens satisfies the following relations: −216≦P2≦−49, 1100≦P4·(hm max)4/(fm·NAm4)≦3800, and 10≦fm≦35, where hmmax [mm] is an effective diameter in the main scanning direction, fm [mm] is a focal length in the main scanning direction, and NAm is a numerical aperture in the main scanning direction, and that a wavefront aberration WFE1 [λrms] in a first wavelength λ1 [nm] satisfies the following relation: WFE1≦0.01.