Triangular Prism Scanner for Stray Light Reduction
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Solution Overview
Problem
Existing optical 3D mapping technologies face geometrical constraints and stray light issues, particularly in compact scanning devices using interference filters.
Innovation Solution
The use of a triangular prism with strategically oriented side faces and a scanning mirror system that leverages total internal reflection (TIR) to selectively refract and reflect optical radiation, allowing for angular selectivity and efficient scanning over a wide range while maintaining a compact structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a compact scanning device uses interference filters, then the device size is reduced, but stray light issues increase and angular selectivity deteriorates
Solution Approach 1:
The patent introduces a triangular prism as an intermediary optical element between the scanning mirror and the scene. This prism mediates the optical path by providing TIR-based angular filtering, which selectively directs different angles of light through different paths, thereby resolving the stray light problem without requiring bulky interference filters
Solution Approach 2:
The patent replaces the traditional interference filter mechanism (which relies on wavelength-based filtering) with a TIR-based angular filtering mechanism. This substitution uses the geometric optics principle of total internal reflection to achieve angular selectivity, eliminating the need for interference filters and their associated stray light issues
2Measurement precision
If a triangular prism with TIR is used, then angular selectivity and stray light reduction are improved, but device complexity increases
Solution Approach 1:
The triangular prism serves multiple functions simultaneously: it acts as an angular filter, a beam director, and a compacting element for the optical path. By integrating these functions into a single optical element, the patent achieves high angular selectivity without proportionally increasing device complexity
Solution Approach 2:
The patent changes the key parameter from wavelength-based filtering (interference filters) to angle-based filtering (TIR). This parameter change fundamentally simplifies the optical system by using the inherent geometric properties of the prism and the laws of optics, rather than requiring complex filter materials and coatings
3Area of stationary object
If the scanning mirror scans over a wide angular range, then coverage area increases, but the beam may exceed the prism's TIR angle and lose selectivity
Solution Approach 1:
The patent addresses the angular range limitation by introducing a second scanning mirror that scans in a perpendicular dimension. This transforms the scanning approach from a single large-angle sweep to a two-dimensional Lissajous pattern, allowing wide coverage while maintaining the narrow angular acceptance required for TIR-based selectivity
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 approach enhances angular selectivity and reduces stray light, enabling effective 3D mapping and depth sensing with improved performance and a low-profile design.
Implementation Method 1
which refracts the beam so that the optical radiation is incident on and reflects from the base
Implementation Method 2
reflects from the base within the prism at a reflection angle that is greater than a total internal reflection (TIR) angle of the prism
Data Source
AI summary
Optical scanning apparatus includes a triangular prism, having first and second side faces and a base. A transmitter directs a beam of optical radiation into the prism through the first side face, which refracts the beam so that the optical radiation is incident on and reflects from the base within the prism at a reflection angle that is greater than a total internal reflection (TIR) angle of the prism and exits the prism through the second side face. At least one scanning mirror is positioned to intercept and reflect the beam back into the prism while scanning the beam over an angular range selected such that after refraction of the scanned beam at the second side face, the scanned beam is incident on the base at a transmission angle that is less than the TIR angle and is transmitted out of the prism through the base.