Optical Finger Navigation Redirection Structure for Compact Illumination
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Solution Overview
Problem
The design of optical finger navigation (OFN) sensors in small form factors faces challenges in efficiently integrating imaging and illumination optics, leading to limitations in light delivery due to total internal reflection and steep angles within the navigation cover, making it difficult to achieve effective illumination of the navigation surface.
Innovation Solution
The implementation of a redirection structure with a small hole in a mirror to guide light from a light source to the navigation surface, using folded optics and mirrors to control stray light and prevent crosstalk, allowing for efficient illumination and processing of light reflections from the navigation surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the size of OFN devices is reduced to achieve small form factor, then the device compactness is improved, but the integration of imaging and illumination optics becomes more difficult and light delivery is limited due to total internal reflection
Solution Approach 1:
The optical system is segmented into separate imaging and illumination subsystems with distinct optical paths. The illumination optics are positioned separately from the imaging optics, allowing independent optimization of each subsystem while maintaining compact overall device size.
Solution Approach 2:
A transparent cover with controlled refraction properties serves as an intermediary element between the light source and navigation surface. This cover redirects illumination light at controlled angles while allowing imaging light to pass through, resolving the conflict between compact illumination path and TIR prevention.
2Length of stationary object
If direct optical path for illumination is used in compact design, then the illumination path length is reduced, but total internal reflection limits the amount of light delivered to the navigation surface
Solution Approach 1:
The illumination path is redirected into a different spatial dimension by utilizing the transparent cover as a refraction interface. Light is delivered through the cover at angles that exploit refraction rather than direct transmission, effectively adding a dimensional aspect to the illumination path that avoids TIR while maintaining compactness.
Solution Approach 2:
The refraction characteristics of the transparent cover are optimized by adjusting its material properties and geometric parameters. By changing the cover's thickness, refractive index, and surface geometry, the system achieves controlled light redirection that delivers sufficient illumination intensity without causing total internal reflection.
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 solution enables effective illumination of the navigation surface even in thin OFN devices, reduces crosstalk, and maintains the compact design of the OFN device, ensuring reliable operation and accurate navigation functionality.
Implementation Method 1
A redirection structure is interposed between the light source and the illumination surface of the navigation cover... The redirection structure defines at least one hole therethrough to pass light generated by the light source toward the illumination surface of the navigation cover
Implementation Method 2
A reflection surface of the first redirection structure is approximately facing the illumination surface of the navigation cover... reflecting light from the tracking surface back toward a reflection surface of the redirection structure
Implementation Method 3
The tracking surface exhibits a first light reflection characteristic in a presence of a navigation object at the tracking surface and a second light reflection characteristic in an absence of the navigation object at the tracking surface
Data Source
AI summary
An optical finger navigation device includes a navigation cover. The navigation cover includes a tracking surface and an illumination surface. The tracking surface exhibits a first light reflection characteristic in a presence of a navigation object at the tracking surface and a second light reflection characteristic in an absence of the navigation object at the tracking surface. A light source generates illumination directed toward the illumination surface of the navigation cover. A redirection structure is interposed between the light source and the illumination surface of the navigation cover. A reflection surface of the first redirection structure is approximately facing the illumination surface of the navigation cover. An illumination surface of the redirection structure is approximately facing the light source. The redirection structure defines at least one hole therethrough to pass light generated by the light source toward the illumination surface of the navigation cover.