Offset Illumination Aperture for Optical Navigation Light Leakage
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Solution Overview
Problem
Optical navigation input devices face challenges in compact design due to light leakage from the tails of the Gaussian beam overwhelming the signal from surface scattering features on specular surfaces like glass, leading to inadequate detection of scattered light.
Innovation Solution
The use of an offset illumination aperture that clips the light beam, producing a diffraction pattern with a discontinuity outside the imaging aperture, allowing only scattered light from surface features to be detected by the image sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a circular illumination aperture is used to truncate the Gaussian beam, then light leakage through the imaging aperture is reduced, but diffraction causes the beam to spread and still allows significant power (about 6 nW per 1 mW beam) to enter the imaging aperture
Solution Approach 1:
The patent applies asymmetry by using a non-circular illumination aperture shape (such as rectangular or polygonal) that is deliberately misaligned with the circular Gaussian beam profile. This asymmetric configuration creates a diffraction pattern where the majority of diffracted light is directed away from the offset imaging aperture, reducing light leakage by more than one order of magnitude compared to circular apertures while maintaining compact device dimensions.
2Object-affected harmful factors
If the optical system is made larger to increase the offset distance between the reflected light beam center and the imaging aperture center, then light leakage is reduced, but the device becomes less maneuverable and less portable
Solution Approach 1:
The patent changes the geometric parameters of the illumination aperture, specifically using non-circular shapes with aspect ratios significantly different from 1:1 (e.g., rectangular apertures with 2:1 or 3:1 aspect ratios). This parameter change creates an anisotropic diffraction pattern that directs light suppression preferentially toward the imaging aperture direction, achieving effective light leakage reduction in a compact form factor without requiring increased system size.
3Object-affected harmful factors
If the offset distance between the illumination aperture and the light beam center is increased to reduce light leakage, then less light enters the imaging aperture, but the illumination spot size increases due to diffraction
Solution Approach 1:
The patent employs asymmetric aperture geometry where the illumination aperture shape and orientation are specifically designed to create directional diffraction. The asymmetric configuration causes diffraction lobes to be oriented perpendicular to the aperture edges, directing the majority of diffracted light away from the imaging aperture while confining the illumination spot growth in the direction parallel to the aperture edges, thus achieving selective light suppression without excessive spot expansion.
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 reduces light leakage, improving the signal-to-noise ratio and enabling effective tracking of movements on smooth surfaces without increasing device size, maintaining portability and maneuverability.
Implementation Method 1
The illumination aperture produces a diffraction pattern relative to the light beam. The diffraction pattern includes a diffraction discontinuity which is substantially free from diffracted light within a sector area outside of the light beam.
Implementation Method 2
These optical devices facilitate tracking input movements on specular navigation surfaces such as glass tabletops which do not have substantial texture for imaging. In general, these optical navigation input devices rely on light scattered by small particles and scratches.
Implementation Method 3
Scattered light reflects off of a surface reflection feature along a scattered light path which is offset from the specular reflection path.
Data Source
AI summary
An optical navigation input device with an offset imaging aperture. The optical navigation input device includes a light source, an illumination aperture structure, and an image sensor. The light source directs a light beam toward a substantially specular illumination surface. Scattered light reflects off of a surface reflection feature along a scattered light path which is offset from a specular reflection path. The illumination aperture structure at least partially defines an illumination aperture interposed between the light source and the illumination surface. The illumination aperture produces a diffraction pattern that includes a diffraction discontinuity which is substantially free from diffracted light within a sector area outside of the light beam. The image sensor is disposed within the scattered light path at a location corresponding to the diffraction discontinuity. The image sensor receives the scattered light from the surface reflection feature and generates a navigation image of the surface reflection feature.