Optical Scanning Apparatus Aberration Correction
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Solution Overview
Problem
Optical scanning apparatuses face challenges in reducing aberrations such as field curvature and distortion in the sub-scanning cross section, especially when using Vertical Cavity Surface Emitting Lasers with large field angles, which affect the optical performance and lead to increased wave aberration and coma aberrations.
Innovation Solution
The optical scanning apparatus incorporates a Vertical Cavity Surface Emitting Laser with a plurality of light-emitting portions spaced in the sub-scanning direction, a light-condensing element, a deflector, and an imaging optical system with non-arc shaped optical surfaces, where the focal length and imaging magnification are optimized to satisfy specific expressions that balance field curvatures and distortions, ensuring opposite variation directions for aberrations caused by different optical systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a Vertical Cavity Surface Emitting Laser with large field angle is used to increase the number of light-emitting portions, then the scanning speed and productivity are improved, but wave aberration and coma aberration increase due to field curvature and distortion
Solution Approach 1:
The patent applies local quality by designing optical elements with different surface curvatures in different regions. Specifically, the incident optical system has a first optical element with a spherical surface that corrects field curvature for off-axis light beams, while the imaging optical system has a second optical element with an aspherical surface that corrects distortion. This localized correction approach allows the system to handle large field angles without excessive aberrations, enabling high productivity while maintaining optical precision.
Solution Approach 2:
The patent employs asymmetry by using optical elements with different surface shapes tailored to specific correction needs. The first optical element uses a spherical surface optimized for correcting field curvature in the incident optical path, while the second optical element uses an aspherical surface for distortion correction in the imaging path. This asymmetric design allows each optical element to be optimized for its specific function, resolving the contradiction between handling large field angles and maintaining image quality.
2Speed
If the number of light-emitting portions is increased to scan the surface more times per unit time, then the printing speed is improved, but the field curvature and distortion aberrations are worsened
Solution Approach 1:
The patent applies parameter changes by optimizing the curvature parameters of optical surfaces. The first optical element has a spherical surface with a specific radius of curvature designed to correct field curvature for multiple light beams, while the second optical element has an aspherical surface with carefully controlled curvature parameters to correct distortion. By adjusting these optical parameters, the system can accommodate increased numbers of light-emitting portions and higher scanning speeds while maintaining aberration correction.
3Device complexity
If a monolithic multi-beam light-source element is used to simplify the structure, then the device complexity is reduced, but the field angle must be limited which restricts the scanning performance
Solution Approach 1:
The patent uses optical elements as intermediaries between the monolithic multi-beam light source and the scanned surface. The incident optical system with its spherical-surfaced element acts as an intermediary to correct field curvature for light beams from multiple emitting portions, while the imaging optical system with the aspherical-surfaced element serves as another intermediary to correct distortion. These intermediary optical elements enable the monolithic light source to achieve large effective field angles without increasing device complexity, thus resolving the contradiction between structural simplicity and scanning performance.
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 corrects and reduces aberrations, providing improved optical performance and uniform image formation even with large field angles, maintaining high-definition pitch and reducing the overall size of the apparatus.
Implementation Method 1
a light-condensing element that converts light beams from the laser source into light beams in another state
Implementation Method 2
a deflector that reflects and deflects the light beams from the first optical system
Implementation Method 3
a second optical system that focuses the light beams deflected by the deflecting member on a surface to be scanned
Data Source
AI summary
At least one exemplary embodiment is directed to an optical scanning apparatus which includes a Vertical Cavity Surface Emitting Laser including a plurality of light-emitting portions that are spaced from each other in at least a sub-scanning direction, a first optical system including a light-condensing element that converts each of light beams from the laser into a light beam in another state; a deflector that reflects and deflects the light beams from the first optical system, and a second optical system that focuses the light beams deflected by the deflecting member on a surface to be scanned, where the second optical system includes at least an imaging optical element having an optical surface with a non-arc shape in a sub-scanning cross section.