Light Guide Beam Shaping for Optical Navigation Noise Reduction
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Solution Overview
Problem
Optical navigation input devices face challenges in tracking movements on smooth surfaces like glass due to rapid fall-off of scattered light intensity away from the specular reflection direction, leading to noise issues and complex packaging requirements for elliptical light beam shapes.
Innovation Solution
The use of a light guide that redirects and refracts an elliptical or circular light beam to illuminate a circular area on the surface at a non-zero angle of incidence, allowing for closer placement of imaging apertures and reducing noise by generating a circular light beam pattern, which simplifies packaging and enhances signal intensity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an illumination aperture is used to adjust the outer intensity profile of the incident light beam, then noise from specular reflection is reduced, but device complexity increases
Solution Approach 1:
The patent extracts and removes the specular reflection component from the light beam path by positioning the imaging aperture to capture only scattered light, excluding the bright specular reflection. This eliminates the need for additional illumination apertures to filter noise, reducing device complexity while maintaining noise reduction effectiveness
Solution Approach 2:
Instead of using an illumination aperture to block specular reflection, the patent inverts the approach by using an imaging aperture that selectively captures only scattered light. This inverted strategy achieves noise reduction by what is admitted rather than what is blocked, simplifying the overall device structure
2Manufacturing precision
If apertures and image sensor are tilted to correlate to the angle of incidence, then proper truncation of the light beam is achieved, but packaging complexity and alignment precision requirements increase
Solution Approach 1:
The patent employs asymmetric positioning where the imaging aperture is offset from the optical axis in a direction perpendicular to the specular reflection. This asymmetric arrangement allows proper beam truncation and scattered light capture without requiring tilted components, simplifying packaging while maintaining manufacturing precision
Solution Approach 2:
Rather than tilting the apertures and sensor to match the angle of incidence, the patent inverts the approach by keeping these components parallel to the navigation surface and instead offsetting the imaging aperture position. This eliminates complex tilting mechanisms and alignment requirements while achieving the same optical effect
3Measurement precision
If the imaging aperture is placed close to the specularly reflected light beam, then scattered light collection is improved, but the imaging aperture encroaches on the specular reflection causing noise
Solution Approach 1:
The patent uses asymmetric positioning of the imaging aperture, offset from the optical axis in a direction perpendicular to the specular reflection. This allows the aperture to be placed close to the specular reflection path to capture scattered light, while the asymmetric offset prevents encroachment on the specular reflection itself, eliminating noise
Solution Approach 2:
The patent applies local quality by creating a specialized region for the imaging aperture with different spatial characteristics than the main optical path. The offset positioning creates a local zone where scattered light can be captured intensively without contamination from specular reflection, optimizing measurement precision while avoiding noise
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 reduces package complexity, allows for more precise tracking on smooth surfaces by collecting scattered light closer to the specular reflection direction, and decreases noise interference, resulting in improved signal intensity and navigation accuracy.
Implementation Method 1
The light guide directs the light beam through a refraction interface in order to illuminate a substantially circular area on the illumination surface
Data Source
AI summary
An optical navigation input device with a light guide which acts as a beam shaping element. The optical navigation input device includes a light source and the light guide. The light source emits a light beam having a substantially elliptical or substantially circular cross section. The light guide is positioned relative to the light source to receive the light beam from the light source in a first direction. The light guide also redirects the light beam in a second direction toward an illumination surface at a non-zero angle of incidence. The light guide directs the light beam through a refraction interface in order to illuminate a substantially circular area on the illumination surface.