Free-Form Optical Element for Laser Scanner Banana Effect Compensation
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Solution Overview
Problem
Laser scanners in motor vehicles face the 'banana effect' due to the inclination of scanning lines, leading to distortion and reduced beam quality, which cannot be fully compensated by single free-form mirrors within limited installation space, and existing compensation methods result in increased beam divergence and low Q factor.
Innovation Solution
An optical element with both reflective and refractive free-form surfaces that compensates for distortions and beam divergence, allowing for targeted light distribution deformation without reducing beam quality, and is designed to reduce beam bundle divergence and enhance homogenization across various scanning angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If a rotatable mirror is inclined at a predetermined fixed angle to achieve the largest possible field of view, then the field of view is improved, but the scanning lines become inclined and distorted (banana effect)
Solution Approach 1:
The optical system is divided into multiple functional components: a free-form surface mirror for distortion compensation, a beam expanding element for divergence control, and a beam combining element. This segmentation allows each component to address specific optical issues independently, resolving the banana effect while maintaining field of view.
Solution Approach 2:
A free-form surface mirror is introduced as an intermediary optical element between the light source and the target field. This mirror specifically compensates for the scanning line distortion caused by the inclined rotatable mirror, acting as a mediator that corrects the optical path without affecting the overall field of view geometry.
2Shape
If optical compensation measures such as curved correction mirrors are used to compensate for distortion, then the scanning line distortion is improved, but the beam bundle divergence increases and Q factor decreases
Solution Approach 1:
The distortion compensation function is separated from the beam quality control function. The free-form surface mirror handles distortion compensation, while a dedicated beam expanding element manages beam divergence. This segmentation prevents the beam bundle quality degradation that occurs when a single curved mirror attempts to perform both functions.
Solution Approach 2:
The curvature and optical parameters of the free-form surface mirror are precisely optimized to provide distortion compensation with minimal impact on beam parameters. By carefully controlling the mirror's surface geometry and position, the system achieves scanning line correction while maintaining beam bundle quality and Q factor.
3Manufacturing precision
If complex optical systems are used to compensate for distortion and maintain beam quality, then the optical performance is improved, but the installation space requirements increase
Solution Approach 1:
Multiple optical functions are merged into a compact integrated optical unit. The free-form surface mirror, beam expanding element, and beam combining element are arranged in a space-efficient configuration that provides distortion compensation and beam quality control within limited installation space, typical of automotive sensor applications.
Solution Approach 2:
The optical elements are arranged in a three-dimensional configuration that optimizes space utilization. By leveraging vertical and depth dimensions rather than only horizontal space, the system achieves complex optical functionality within a compact footprint suitable for automotive installations.
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 optical element effectively compensates for the banana effect, maintaining high beam quality and reducing divergence to less than 0.2° across a wide emission angle range, while minimizing installation space requirements.
Implementation Method 1
a first side (13a) having a reflective first free-form surface (F1)... to reflect the beam bundle transmitted through the second free-form surface up to the first free-form surface on the first free-form surface
Implementation Method 2
a second side (13b), opposite to the first side (13a), having a refractive second free-form surface (F2)... to transmit a beam bundle incident on the second side (13b) on the optical element (13) at least in large part through the second free-form surface (F2) up to the first free-form surface (F1)
Data Source
AI summary
The invention relates to an optical element (13) for an emitting unit (8) of an optical acquisition device (3), wherein the optical element (13) comprises a first side (13a) having a reflective first free-form surface (F1) and a second side (13b), which is opposite to the first side (13a), having a refractive second free-form surface (F2). Furthermore, the optical element (13) is designed to transmit a beam bundle (10) incident on the second side (13b) on the optical element (13) at least in large part through the second free-form surface (F2) up to the first free-form surface (F1), to reflect the beam bundle (10) transmitted through the second free-form surface (F2) up to the first free-form surface (F1) at the first free-form surface (F1), and to emit the beam bundle (10) reflected from the first free-form surface (F1) via the second free-form surface (F2). In this case, the first free-form surface (F1) is designed to increase a divergence of the beam bundle (10) incident on the first free-form surface (F1), and the second free-form surface (F2) is designed, upon emission of the beam bundle (10) reflected from the first free-form surface (F1), to reduce the divergence increased during the reflection.