Lensless Optical Navigation Device Using Total Internal Reflection
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Solution Overview
Problem
Current navigation devices in mobile and computer devices face issues such as unreliability, high cost, and size constraints, particularly with trackballs, joysticks, and capacitance-based touch areas, while conventional optical navigation devices are thick due to LED light sources and collimation optics.
Innovation Solution
An optical navigation device utilizing a laser, image sensor, and optical element with total internal reflection (TIR) surfaces, where the angle between the laser's principal optical axis and the first TIR surface is between 30° and 40°, allowing for compact design, reduced thickness, and elimination of the need for reflective coatings, using inexpensive materials like polycarbonate or PMMA.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If conventional optical navigation devices use LED light sources with collimation and imaging optics, then the navigation function is achieved, but the device thickness increases
Solution Approach 1:
The patent extracts and eliminates the collimation and imaging optics from the conventional optical navigation system. By using a laser source that inherently provides sufficient directionality and by directly imaging the interference pattern onto the sensor without additional lenses, the device thickness is reduced while maintaining navigation functionality.
Solution Approach 2:
The optical element serves multiple functions simultaneously: it acts as a beam splitter to create interference patterns, provides total internal reflection surfaces for light guidance, and functions as the imaging element. This multi-functionality eliminates the need for separate collimation and imaging optics, reducing device thickness.
2Ease of manufacture
If reflective coatings are applied to TIR surfaces, then reflection efficiency is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The optical element utilizes total internal reflection, a self-service mechanism where the refractive index difference between the optical material and surrounding medium automatically provides the necessary reflection. No external reflective coatings are needed, as the physics of TIR inherently ensures reliable reflection when the angle of incidence exceeds the critical angle.
Solution Approach 2:
The patent changes the operating parameters by designing the optical element geometry and light path such that the angle of incidence at the TIR surfaces is maintained above the critical angle. This parameter control ensures reliable total internal reflection without requiring reflective coatings, simplifying manufacturing.
3Length of moving object
If the angle between laser optical axis and first TIR surface is optimized for compact design, then device height is reduced, but illumination of second TIR surface may be insufficient
Solution Approach 1:
The patent optimizes the angular relationship between the laser optical axis and the first TIR surface (set at 30-40 degrees) to efficiently direct light onto the second TIR surface. This angular optimization ensures that even in a compact device height configuration, the second TIR surface receives sufficient illumination for reliable frustrated total internal reflection detection.
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
The solution enables a reliable, cost-effective, and miniaturized optical navigation device capable of capturing multiple finger print ridge periods, suitable for mobile communications devices, with a low device height and simplified manufacturing process.
Implementation Method 1
the optical element, laser and image sensor are together arranged to direct radiation emitted by the laser onto the imaging surface at least partly by total internal reflection by the first and second TIR surfaces
Implementation Method 2
a laser having a principal optical axis
Implementation Method 3
an image sensor having an imaging surface
Data Source
AI summary
An optical navigation device for use with mobile telephones and the like is disclosed, which has a reduced height as compared with current designs. The navigation device comprises a laser such as a VCSEL laser, an exposed user surface and two other surfaces that provide for total internal reflection of the incident laser beam. The surfaces are constructed with shallower than normal angles, preserving the basic functionality of the device while reducing the height.