Reflective Optical Filter Element for Narrowband Wide-Field Detection
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Solution Overview
Problem
Existing camera systems for autonomous vehicles struggle with insufficient ambient light suppression and interference, limiting their effective range and accuracy in distance measurements due to the high detection light conductance and susceptibility to interference from other vehicles.
Innovation Solution
The optical system employs a reflective filter element arranged outside the entrance pupil, utilizing spherical filter layers with centers of curvature in the entrance pupil, and a retroreflective design to achieve very narrow-band filtering with high light conductance, allowing for improved ambient light suppression and reduced interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a narrowband spectral filter with 1 nm bandwidth is placed in the pupil plane, then the spectral filtering performance is improved, but the field of view is reduced to approximately 5°
Solution Approach 1:
The filter element is moved from the pupil plane (2D aperture space) to an intermediate image plane (3D spatial space with different optical path characteristics). This dimensional transition allows the filter to operate on already-converged light rays, decoupling the angular acceptance from the spectral filtering function and enabling narrowband filtering with wide field of view.
Solution Approach 2:
An intermediate image plane is introduced as a mediator between the objective lens and the sensor. The filter element is positioned at this intermediate plane where light rays from different field angles have already converged to different spatial locations, allowing the filter to process each angle's light independently without cross-talk, thus maintaining wide field of view while achieving narrowband filtering.
2Measurement precision
If the filter is placed close to the sensor plane, then the angular range is reduced to a maximum aperture of 1/10.6, but typical apertures for this application are in the range of 1/1.5 to 1/2.4
Solution Approach 1:
The filter positioning is changed from the sensor plane (final image space with strict angular constraints) to an intermediate image plane (conjugate space with different angular magnification). This allows the system to use large-aperture lenses (f/1.5-f/2.4) while the filter still operates on effectively collimated or semi-converged rays, maintaining both high aperture and narrowband filtering performance.
3Ease of manufacture
If a dichroic detection filter with a bandwidth of approximately 50 nm is used, then the manufacturing is simplified, but the ambient light suppression is insufficient for ranges beyond 40 m
Solution Approach 1:
The filter bandwidth parameter is changed from 50 nm (standard dichroic filter) to 1 nm (narrowband interference filter). Although narrowband filters are more complex to manufacture, the patent shows that positioning the filter at the intermediate image plane rather than the pupil plane enables this narrow bandwidth to be achieved while maintaining wide field of view and high aperture, thus achieving both good manufacturability and excellent ambient light suppression.
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 design enables a large image field with high aperture and light intensity while achieving very narrow-band detection, enhancing the effective range and reducing interference, thereby improving the accuracy and efficiency of distance measurements.
Implementation Method 1
spherical filter layers with centers of curvature in the entrance pupil
Implementation Method 2
very narrow-band filtering with a high light conductance
Implementation Method 3
retroreflective design to achieve very narrow-band filtering with high light conductance
Implementation Method 4
the phase of the light scattered back from the object is evaluated
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The invention relates to an optical system with an entrance pupil (9), which has a first aperture diameter (D1), an exit pupil (10) and a reflective or transmissive filter element (6) spaced at a distance from the entrance pupil (9), which is designed and arranged such that a second diameter (D2) is illuminated on the filter element (6) by a beam passing through the entrance pupil (9) and spreading divergently from this, wherein the second diameter (D2) corresponds to n times the first aperture diameter (D1) and n is an number greater than 1, as a result of which the local angular spectrum at each point on the filter element (6) is n times smaller in comparison to the entrance pupil (9), wherein the filter element (6) selectively reflects or transmits to the exit pupil (10) at each point only a predetermined spectral range and wherein an optical imaging unit (3) comprising the filter element (6) is provided, which images the entrance pupil (9) onto the exit pupil (10).